shear heating and clumped isotope reordering in carbonate faults abstract natural faults are expected to heat rapidly during seismic slip and to cool quite quickly after the slip event here we examine clumped isotope thermometry for its ability to identify such short duration elevated temperature events along frictionally heated carbonate faults our approach is based on measured 47 values that reflect the distribution of oxygen and carbon isotopes in the calcite lattice measuring the abundance of 13c 18o bonds which is affected by temperature we examine three types of calcite rock samples 1 crushed limestone grains that were rapidly heated and then cooled in static laboratory experiments simulating the temperature cycle experienced by fault rock during an earthquake slip 2 limestone samples that were experimentally sheared to simulate earthquake slip events and 3 samples from fault mirrors fms collected from principle slip surfaces of three natural carbonate faults extensive fm surfaces are believed to form during earthquake slip our experimental results show that 47 values decrease rapidly in the course of seconds with increasing temperature and shear velocity on the other hand carbonate shear zones from natural faults do not show such 47 decrease we suggest that the 47 response may be controlled by nano size grains the high abundance of defects and highly stressed strained grain boundaries within the carbonate fault zone that can reduce the activation energy for diffusion and thus lead to an increased rate of isotopic disordering during shear experiments in our laboratory experiments the high stress and strain on grain contacts and the presence of nanograins thus allows for rapid disordering so that a change in 47 occurs in a very short and relatively low intensity heating events in natural faults it may also lead to isotopic ordering after the cessation of frictional heating thus erasing the high temperature signature of 47

reconstructing fluid expulsion and migration north of the variscan orogen northern england abstract lower carboniferous platform carbonates in northern england host lead zinc fluorite barite deposits that have previously been classified as mississippi valley type mvt the controls on the distribution of low temperature particularly mvt minerals have long been debated but the interplay of basin evolution and fluid movement is often neglected early carboniferous sedimentation on the derbyshire platform took place within a back arc extensional regime north of the northward migrating variscan orogenic front which increasingly influenced fluid movement on the platform throughout the carboniferous it is the interplay of fluid movement cementation and variscan tectonism that is the focus of this paper which aims to reconstruct fluid movement within a basin moving from an extensional to a compressional regime in particular it demonstrates the variability of fluid flux during post rift subsidence and basin inversion and the corresponding influences of this upon mineral distribution during early burial of the derbyshire platform pore filling cements were precipitated from meteoric porewaters driven downdip from the east under topographic drive these cements occluded most interparticle porosity and therefore permeability became fracture controlled the waning effects of extensional tectonism during post rift subsidence permitted intermittent expulsion of small volumes of trace metal charged carbonate saturated fluids from overpressured contemporaneous clastic basins adjacent to the derbyshire platform overall however waning tectonism meant that the volume of fluids released during this period remained minor with the onset of the variscan orogeny and resultant compressional tectonism and basin inversion caledonian basement fault systems were reactivated channeling large volumes of trace metal charged fluids from the basins onto the derbyshire platform establishing an east west component to fluid flow the reconstruction of fluid expulsion and migration within this tectonically active regime demonstrates variations in fluid source and migration pathways during basin evolution consequently fluid movement is complex with the platform receiving fluids from a variety of sources this highlights the importance of understanding both the temporal and the spatial variations in cement chemistry when reconstructing flow the results of this study have relevance to other mineralized carbonate platforms in extensional and compressional settings worldwide and especially to sedimentary basins that host mvt deposits and hydrocarbons where it is crucial to understand the timing and mechanisms of diagenetic cementation and hydrocarbon emplacement

the influence of source depositional conditions on the hydrocarbon and nitrogen compounds in petroleum from central montana usa abstract the hydrocarbon and pyrrolic nitrogen compound compositions of 21 crude oils from reservoirs in the heath tyler amsden and swift morrison formations of central montana have been investigated by combined gas chromatography mass spectrometry the biomarker and aromatic hydrocarbon data enabled recognition of three composition types within the heath tyler amsden oils the swift morrison oils displayed different hydrocarbon characteristics and are classified as a separate oil group a number of geochemical parameters e g dibenzothiophene phenanthrene c 20 triaromatic steroid hydrocarbon c 20 c 28 triaromatic steroid hydrocarbons indicate strong variations in petroleum composition from north to south across the region oils from the central montana uplift with high relative c 27 diasteranes c 29 steranes and ts ts tm suggests increasing clay contribution to the source while abundant gammacerane indicates the development of hypersaline conditions with restricted circulation oils from the bull mountain basin represented by the amsden oils show relatively low c 27 diasteranes c 29 steranes and ts ts tm ratios indicating increasing carbonate contribution to the source while the decrease of a gammacerane contribution suggests decreasing salinity levels which may explain the dominance of tricyclic terpane and hence their precursors to the source organic matter while the changes recorded by the biomarker and aromatic hydrocarbon compositions show strong regional variations the nitrogen compounds do not respond so strongly however weak trends coinciding with source carbonate content were apparent in the following ratios 1 8 dimethylcarbazole 1 8 dimethylcarbazole 1 ethylcarbazole and carbazole sum of c 2 carbazoles the second parameter may be responding to variations in salinity since it co varies with the behaviour exhibited by the tricyclic terpanes the source information that can be extracted from biomarkers and aromatic hydrocarbons suggests that primary migration and compositional fractionation during expulsion has exerted little influence on this fraction of petroleum meanwhile primary migration and compositional fractionation during expulsion appear to effect the carbazole and benzocarbazole distributions thereby limiting their application as indicators for source rock facies composition

fissure fills along faults variscan examples from gower south wales the extent to which persistent rather than transient fissures wide planar voids can exist along upper crustal faults is important in assessing fault permeability to mineral and hydrocarbon bearing fluids variscan late carboniferous faults cutting dinantian lower carboniferous limestones on the gower peninsula south wales host clear evidence for fissures up to several metres wide evidence includes dendritic hematite growth and elongate calcite growth into open voids spar ball and cockade breccia formation laminated sediment infill and void collapse breccias detailed mapping reveals cross cutting geometries and brecciation of earlier fissure fills showing that fissures were formed during rather than after active faulting fissures therefore probably formed by geometric mismatch between displaced fault walls rather than by solution widening along inactive faults

upper oligocene lacustrine source rocks and petroleum systems of the northern qaidam basin northwest china our organic geochemical study of oils from the northern qaidam basin defines a family of genetically related oils that contain biomarkers indicative of source rocks deposited in tertiary hypersaline anoxic lacustrine settings although cenozoic outcrop samples from northern qaidam are too organic lean to be of source quality dark laminated upper oligocene mudstones containing gypsum crystals and pyrite from the shi 28 well yield total organic carbon toc and rock eval data indicative of fair to good source rocks organic matter is derived from algae and bacteria and there apparently was little contribution from terrestrial material biomarker data provide a good correlation between the produced oils and the upper oligocene shi 28 core samples hydrocarbons derived from these source rocks are contained in upper oligocene miocene and pliocene reservoirs although eight of the oil samples are from the northwest corner of the basin one sample in this genetic family of hypersaline oils comes from northeast qaidam an area previously believed to only produce oils derived from jurassic freshwater lacustrine source rocks this sample thus indicates the presence of an unidentified and undocumented source rock in the northeast part of the basin hypersaline oils and the associated source rocks have low biomarker maturity parameters thermal modeling indicates that hydrocarbon generation probably occurred in northwestern qaidam within the last 3 million years

taking the temperature of hydrothermal ore deposits using clumped isotope thermometry better tools are needed to map the thermal structure of ore deposits here carbonate clumped isotope thermometry is applied for the first time in epithermal skarn and carbonate hosted deposits to identify the conditions involved in metal transport and deposition clumped isotope temperature calibrations were tested by measurement of carbonates from three geothermal fields in the taupo volcanic zone new zealand that record growth temperatures between 130 and 310 c results for modern taupo volcanic zone calcites were paired with known fluid 18o values and these indicate precipitation in equilibrium with produced geothermal waters measurements carried out at the waihi low sulfidation deposit in new zealand the antamina polymetallic skarn in peru and the mount isa sediment hosted pb zn and cu deposit in queensland australia demonstrate that clumped isotope values are sensitive to temperature gradients defined using other methods at waihi an andesite hosted deposit temperature controls the majority of variation in carbonate mineral 18o at mount isa 300 to 400 c temperatures were recorded in a 1 5 ga orebody which are consistent with fluid inclusion values highlighting the longevity of clumped isotope archives in dolomite minerals collectively these results demonstrate the potential for clumped isotopes to delineate the heat footprint around deposits that contain carbonates and to more effectively disentangle magmatic and meteoric fluid 18o signals

source rock palaeoenvironments and controls on the distribution of dibenzothiophenes in lacustrine crude oils bohai bay basin eastern china abstract the applicability of sulphur aromatic parameters based on ratios of dibenzothiophene dbt and its alkylated homologues as indicators of oil maturity has been investigated in 27 oils from the damintun and zhuanhua depressions bohai bay basin the oils were characterised by bulk composition and environmentally sensitive aliphatic biomarkers and were derived from a wide range of lacustrine source depositional environments ranging from highly reducing hypersaline sulphur rich oils to terrestrial input dominated freshwater very high wax oils with maturities ranging from immature to probable mid mature dibenzothiophene based maturity parameters are not well correlated with sterane isomerization ratios and immature oils in particular could not be discriminated by these aromatic maturity indicators in contrast dbt based parameters are strongly correlated with pristane to phytane and ts tm ratios high methyldibenzothiophene ratios mdr are associated with fresh water source deposition whilst low mdrs are found in oils of hypersaline source affinity unusually high relative concentrations of 2 3 mdbt were observed in some of the immature oils inferred to be sourced by lacustrine organic laminites the data provide further evidence that thermal stress is not the sole factor controlling the distribution patterns of dibenzothiophenes in oils and that source depositional environments can exert a dominant influence when their range of variation is large absence of dbt in some biodegraded oils is tentatively attributed to its aqueous solubility during associated water washing

geochemical comparison of fluid inclusion and present day oil accumulations in the papuan foreland evidence for previously unrecognised petroleum source rocks abstract petroleum production in papua new guinea is limited to the papuan fold belt present day oil accumulations in fields such as iagifu hedinia and gobe are thought to be mainly derived from clay rich jurassic marine source rocks containing terrestrially derived organic matter that were deposited under oxic conditions in this study other generative source rocks in the papuan foreland are indicated using fluid inclusion fi oil data from three wildcat wells koko 1 bujon 1 and kimu 1 which were drilled on the bosavi arch detailed organic geochemistry of these fi oils and associated free oils or oil stains suggests that none of these were generated from the aforementioned jurassic source rocks instead at least three different generative source rocks are indicated firstly a marine probably late cretaceous or younger source rock deposited under reducing conditions is indicated by the bujon 1 fi oil this source rock had a moderate contribution from higher plant organic matter including oleanane and or lupane the bujon 1 fi oil has similarities with fi oils from the iagifu 7x and p nyang 2x wells in the papuan fold belt secondly an algal dominated lacustrine source rock is indicated by the biodegraded koko 1 rft crude oil the unbiodegraded fi oil from koko 1 and the bujon 1 oil stains from the toro and imburu formations these lacustrine oils have high abundances of tricyclic terpanes pregnane homopregnane and gammacerane contain carotane and have high c26 c25 tricyclic terpane ratios the source of the lacustrine oils is inferred to contain moderate amounts of terrestrial organic matter indicated by a dominance of c29 steranes and abundant aromatic higher plant biomarkers and could be gypsiferous shales embedded in oligocene miocene carbonates or triassic age sediments deposited on igneous basement during early rifting associated with the break up of gondwana the kimu 1 fi oil was generated from a mature marine suboxic source rock but has a different geochemical composition to free oil from a similar interval which was derived from a carbonate rich source rock none of the fi oils correlate well with oil families previously described in papua new guinea accordingly the oils recovered from fis in this part of the papuan basin support the presence of laterally varying source rock compositions and qualities and indicate that there are opportunities to develop new charge models for features across the papuan foreland furthermore koko 1 bujon 1 and kimu 1 fi oils have different geochemical compositions compared to the associated free oils or oil stains indicating that each of these localities has a multi phase charge history further work to lower exploration risk in the papuan foreland should be directed to understanding the distribution maturity and expulsion history of these newly recognised potential source rocks

charging of the penglai 9 1 oil field bohai bay basin china functions of the delta on accumulating petroleum abstract the penglai 9 1 pl9 1 oil field which contains china s third largest offshore oil accumulation in place reserves greater than 2 28 10 8 ton or 1 49 10 9 bbl was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl9 1 field contains two oil bearing series the granite intrusions in mesozoic mz and both the sandstone reservoirs in neogene guantao ng and neogene minghuazhen nm formation the origins of the pl9 1 field both in terms of source rock intervals and generative kitchens were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples the mesozoic granite intrusions which hold more than 80 of the oil reserves in the field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression the neogene reservoirs of the pl9 1 field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression and in the south by oil generated from the first member es 1 of the shahejie formation in the miaoxibei depression interactive contact between the large fan delta and the mature source rocks residing in the es 3 formation of the bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the pl9 1 field which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east china

clumped isotope evidence for episodic rapid flow of fluids in a mineralized fault system in the peak district uk we have used clumped isotope thermometry to study a fault hosted hydrothermal calcite vein associated with the mississippi valley type mvt mineralization on the derbyshire platform in the southern pennines uk this is the first published dataset obtained using a new mass spectrometer mira optimized for clumped isotope analysis and an associated clumped isotope temperature calibration we analysed multiple generations of vein growth at high spatial resolution in two transects across the vein the vein grew episodically at temperatures between 40 and 100 c we interpret each episode of growth as being associated with an increasing flux of formation waters from deep sedimentary basins next to the mineralized platform and an accompanying increase in the precipitation temperatures heat is conserved in the fluid as it ascends along the fault surface and thus flow must have been fast and restricted to short lived pulses the flux could have been driven by high pore pressures associated with rapid sedimentation hydrocarbon generation and diagenesis in the basinal facies of the visean bowland hodder group natural hydraulic fracturing of shale units and failure of capillary seals possibly triggered by uplift allowed the release of fluids into aquifers within the sediment pile the transmission of high pore fluid pressures from the shales to the fault zone aided by the compressibility of the gas phase in two phase pore fluids may have resulted in fault rupture accompanied by enhanced fracture permeability and rapid fluid flow vein growth ceased as pore pressures dissipated such behaviour is closely related to a seismic valve type model for mineralization supplementary material details of the methods and equipment are available at https dx doi org 10 6084 m9 figshare 3808329 v9

laboratory calibration of the calcium carbonate clumped isotope thermometer in the 25 250 c temperature range abstract many fields of earth sciences benefit from the knowledge of mineral formation temperatures for example carbonates are extensively used for reconstruction of the earth s past climatic variations by determining ocean lake and soil paleotemperatures furthermore diagenetic minerals and their formation or alteration temperature may provide information about the burial history of important geological units and can have practical applications for instance for reconstructing the geochemical and thermal histories of hydrocarbon reservoirs carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of carbonate minerals without requiring a priori knowledge of the isotopic composition of the initial solution it is based on the temperature dependent abundance of the rare 13c 18o bonds in carbonate minerals specified as a 47 value the clumped isotope thermometer has been calibrated experimentally from 1 c to 70 c however higher temperatures that are relevant to geological processes have so far not been directly calibrated in the laboratory in order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high temperature geological processes we precipitated caco3 mainly calcite in the laboratory between 23 and 250 c we used two different precipitation techniques first minerals were precipitated from a caco3 supersaturated solution at atmospheric pressure 23 91 c and second from a solution resulting from the mixing of cacl2 and nahco3 in a pressurized reaction vessel at a pressure of up to 80 bar 25 250 c the calibration lines of both experimental approaches overlap and agree in the slopes with theoretical estimates and with other calibration experiments in which carbonates were reacted with phosphoric acid at temperatures above 70 c our study suggests a universal 47 t calibration t in k 47 in 47 0 98 0 01 3 407 10 9 t 4 2 365 10 7 t 3 2 607 10 3 t 2 5 880 t 0 293 0 004 this new 47 t calibration given in the absolute reference frame that extends the experimentally calibrated temperature range for clumped isotopes to 250 c can be applied to carbonates that grew at intermediate temperatures 20 250 c

lower middle jurassic nonmarine source rocks and petroleum systems of the northern qaidam basin northwest china the qaidam basin is a nonmarine petroliferous basin on the northeastern margin of the tibet plateau potential source rocks are reported from tertiary saline lacustrine deposits and jurassic freshwater lacustrine or terrestrial strata the jurassic source rock is similar in terms of depositional system lithology age and organic geochemistry to nonmarine jurassic rocks that are thought to be potentially significant hydrocarbon sources in many basins of central asia including the tarim junggar and other important petroleum producing basins these jurassic source rocks were deposited in freshwater lacustrine systems in intracontinental foreland style basins during the early and middle jurassic these lacustrine strata are associated with coals and coaly mudstones with possible secondary importance as hydrocarbon source rocks oils from the northern qaidam basin can be divided into two groups based on molecular indicators of depositional environment and age diagnostic biomarkers those derived from this jurassic freshwater lacustrine source rock and those derived from a tertiary hypersaline lacustrine source rock the correlation of some qaidam oils to a jurassic source establishes a petroleum system involving these nonmarine jurassic source rocks oils of this petroleum system have been produced from tertiary and mesozoic reservoirs in anticlinal and thrust related traps in northeastern qaidam maturation modeling of the jurassic source rock indicates that these oils were generated and expelled during the miocene pliocene in much of northern qaidam the geological context of the basin suggests that drainage within the basin primarily was vertical probably mainly along faults until evaporite or overpressured shale seals were encountered in the overlying cenozoic section documentation of this petroleum system suggests other exploration targets remain underevaluated in northern and southwestern qaidam furthermore the northern qaidam petroleum system is a useful analog to interpret the role of similar jurassic source rocks in other sparsely documented basins of central asia

controls on organic matter enrichment in source rocks of the shahejie formation in the southwestern bozhong sag bohai bay basin china abstract with the discovery of the bozhong 19 6 large gas field in the bohai bay basin the study of lacustrine source rocks in the southwestern bozhong sag has garnered new interest in this paper 107 source rock samples of the paleogene shahejie formation es from the southwestern bozhong sag were analyzed with organic and inorganic methods and compared with other sags in the bohai bay basin to reveal the depositional environment and controlling factors of organic matter enrichment during the deposition of the es the formation of source rocks average total organic content 2 76 was subject to a combination of high organic productivity and enhanced organic preservation also this was reflected by the existence of nutrient elements of p and ba as well as other high productivity related elements such as cu zn and ni the moderate mo enrichment factor pr ph and low to moderate c p org ratios were an essential part of this organic preservation moreover the evidence we observed for the existence of hydrothermal activities consisted of high contents of quartz and pyrite large positive eu anomalies and enrichment of elements related to hydrothermal fluids hydrothermal influence may lead to similarities and fluctuations in water salinity organic productivity and preservation in the third es3 and first es1 members of the es hydrothermal fluids may play an essential role in promoting the development of high organic productivity stable reducing environment and brackish water as shown by the range of b ga and ts toc in the lakes during the source rock deposition this paper may provide implications for gas accumulation mechanisms and a complete set of organic and inorganic experimental data for source rock analysis in other lacustrine rift basins

early cenozoic two phase extension and late cenozoic thermal subsidence and inversion of the bohai basin northern china abstract the bohai basin is one of a family of early cenozoic extensional basins that lie along the eastern margin of asia from russia to vietnam initial extension was probably triggered by subduction roll back of the oceanic pacific plate from the asian continent there were two phases in the bohai basin s rift history the earlier paleocene early eocene phase resulted in the deposition of the kongdian formation and the fourth lowest member of the shahejie formation in a series of elongate half grabens these half grabens have master faults with a nne ssw orientation secondary normal faults are typically clockwise oblique to the master faults indicating a component of dextral transtension deposition was focused in the west and south of the present basin these rocks are mainly alluvial fan and fluvial red beds the architecture of the basin underwent an important change at ca 43 45 ma middle eocene beginning with the deposition of the third member of the shahejie formation in part these sediments were deposited in the same half grabens as the kongdian formation but the bozhong depression in the central part of the basin originated at this time and became the major depocentre the bozhong depression superficially resembles a pull apart basin it formed when continued transtension of the earlier tertiary fault systems to the east and west created an extensional overlap between them during this phase the basin as a whole had a geometry with elements typical of both pull apart and transtensional basins regional extension in many east asian basins ended at the end of the oligocene probably because of the onset of transpression within eastern asia caused by the collision of australia with the philippine sea plate dextral transpression caused minor inversion of some of the earlier normal faults in bohai but as a whole the basin began to subside in a post rift phase of thermal subsidence that has lasted until the present day

barrier island arcs along abandoned mississippi river deltas abstract generation of transgressive barrier island arcs along the mississippi river delta plain and preservation of barrier shoreline facies in their retreat paths on the inner shelf is controlled by 1 shoreface translation 2 age of the transgression and 3 the thickness of the barrier island arc sediment package barrier island arcs experience an average relative sea level rise of 0 50 1 00 cm yr 1 and shoreface retreat rates range from 5 15 m yr 1 young barrier island arc sediment packages isles dernieres are thin and have experienced limited landward retreat of the shoreface older barrier island arcs chandeleur islands are thicker and have experienced significant landward movement of the shoreface because of the greater time available for retreat if the transgressed barrier shoreline sediment package lies above the advancing ravinement surface the entire sequence is truncated a thin reworked sand sheet marks the shoreface retreat path the base of the transgressive sediment package can lie below the ravinement surface in older barrier shorelines in this setting the superstructure of the barrier shoreline is truncated leaving the basal portion of the transgressive sequence preserved on the inner shelf a variety of transgressive stratigraphic sequences from sand sheets to truncated barrier islands to sand filled tidal inlet scars have been identified by high resolution seismic profiling across the shoreface retreat paths of mississippi delta barrier island arcs one of these examples the isles dernieres represents a recently detached barrier island arc in the early stages of transgression an older example the chandeleur islands represents a barrier island arc experiencing long term shoreface retreat this paper describes the stratigraphic character and preserved transgressive facies for the isles dernieres and chandeleur islands

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

a revised chronology for mississippi river subdeltas radiocarbon measurements by accelerator mass spectrometry relating to three of the four late holocene mississippi river subdeltas yielded consistent results and were found to differ by up to 2000 carbon 14 years from previously inferred ages these geological dataare in agreement with archaeological carbon 14 data and stratigraphic ages based on ceramic seriation and were used to develop a revised chronologic framework which has implications for prehistoric human settlement patterns coastal evolution and wetland loss and sequence stratigraphic interpretations

the diagenesis of the late dinantian derbyshire east midland carbonate shelf central england carbonate cements in late dinantian asbian and brigantian limestones of the derbyshire carbonate platform record a diagenetic history starting with early vadose meteoric cementation and finishing with burial and localized mineral and oil emplacement the sequence is documented using cement petrography cathodoluminescence trace element geochemistry and c and o isotopes the earliest cements pre zone 1 are locally developed non luminescent brown sparry calcite below intrastratal palaeokarsts and calcretes they contain negligible fe mn and sr but up to 1000 ppm mg their isotopic compositions centre around 18o 8 5 13c 5 0 calcretes contain less 13c subsequent cements are widespread as inclusion free low mg low fe crinoid overgrowths and are described as having a dead bright dull cathodoluminescence the dead cements zone 1 are mostly non luminescent but contain dissolution hiatuses overlain by finely detailed bright subzones that correlate over several kilometres across dead bright subzones there is a clear trend in mg 500 900 ppm mn 100 450 ppm and fe 80 230 ppm zone 1 cements have isotopic compositions centred around 18o 8 0 and 13c 2 5 zone 2 cement is bright thin and complexly subzoned it is geochemically similar to bright subzones of zone 1 cements dull zone 3 cement pre dates pressure dissolution and fills 70 or more of the pore space it generally contains little mn fe and sr but can have more than 1000 ppm mg increasing stratigraphically upwards the 18o compositions range from 5 5 to 15 and the 13c range is 1 to 3 20 00 zone 4 fills veins and stylolite seams in addition to pores it is synchronous with pb ba f ore mineralization and oil migration zone 4 is ferroan with around 500 ppm fe up to 2500 ppm mg and up to 1500 ppm mn isotopic compositions range widely 15o 2 7 to 9 and 13c 3 8 to 2 50 unaltered marine brachiopods suggest a dinantian seawater composition around 15o 0 smow but vital isotopic effects probably mask the original 13c pdb value pre zone 1 calcites are meteoric vadose cements with light soil derived 13c and light meteoric 18o an unusually fractionated pluvial 15o smow value of around 6 is indicated for local dinantian meteoric water calcrete 18o values are heavier through evaporation zone 1 textures and geochemistry indicate a meteoric phreatic environment fe and mn trends in the bright subzones indicate stagnation and precipitation occurred in increments from widespread cyclically developed shallow meteoric water bodies meteoric alteration of the rock body was pervasive by the end of zone 1 with a general resetting of isotopic values zone 3 is volumetrically important and external sources of water and carbonate are required emplacement was during the namurian early westphalian by meteoric water sourced at a karst landscape on the uplifted eastern edge of the derbyshire east midland shelf the light 18o values mainly reflect burial temperatures and an unusually high local heat flow but an input of highly fractionated hinterland derived meteoric water at the unconformity is also likely relatively heavy 13c values reflect the less altered state of the source carbonate and aquifer zone 4 is partly vein fed and spans burial down to 2000 m and the onset of tectonism light organic matter derived 13c and heavy 18o values suggest basin derived formation water combined with textural evidence of geopressures this relates to local high temperature ore mineralization and oil migration low water to rock ratios with host rock buffering probably affected the final isotopic compositions of zone 4 masking extremes both of temperature and organic matter derived co2

oil source rock correlations limitations and recommendations a rigorous defensible and causal oil source rock correlation definitively ties an individual source rock sample to an individual crude oil using genetically based internally consistent parameter matches such a correlation is a relationship established between the two components which is consistent with all known chemical geochemical and geological information and meets three criteria a the relationship must be causal the oil must arise at least in part from the specified source rock s b chemical data used in the correlation must be comparable the elemental molecular and isotopic data derived from the source rock must be of the same type as that derived from the oil and c all available geological data must be supportive clear geological evidence must exist which allows the proposed source rock to have sourced the oil the three points of this definition are satisfied and the correlation is successful if we solve one analytical and three geological problems natural extraction of crude oil from its source rock i e expulsion differs mechanically and temporally from laboratory extraction leading to a correlation problem referred to as extraction differences and representing the single greatest analytical uncertainty in correlation efforts geologically three aspects confound oil source correlations occurrence of multiple source units and or source units at differing maturity levels lateral and vertical depositional variations in source unit s organic matter and lateral and vertical variation in reservoir unit s organic matter these concerns are overcome by taking five actions for each oil source correlation effort 1 select representative samples using statistically defensible methods 2 establish the inherent compositional variability laterally and temporally due to depositional and maturation processes in each prospective source unit 3 assess the extent of migration induced changes in oil composition including post migration changes such as in reservoir alteration 4 support each correlation with migration histories derived from 4d models 5 iterate correlation results with new data gathered from ongoing exploration efforts these five actions will a allow correlation success to be measured more objectively b establish risking parameters for direct use in basin assessment and c provide baseline criteria for use in assessing the reliability of oil source rock correlations although these approaches will improve conventional oil source rock correlation efforts ultimately they may not be needed if inversion methods become more reliable the ability to invert compositional data for crude oil i e predict the age lithology maturity and other characteristics of a source rock solely through chemical analysis of its expelled oil could eventually result in successful oil source rock correlations in which source rock analysis for oil source rock correlation purposes is less critical

carbonate clumped isotope bond reordering and geospeedometry carbonate clumped isotope thermometry is based on the preference of 13c and 18o to form bonds with each other at elevated temperatures such bond ordering is susceptible to resetting by diffusion of c and o through the solid mineral lattice this type of bond reordering has the potential to obscure primary paleoclimate information but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates we determined arrhenius parameters for solid state reordering of c o bonds in two different calcites through a series of laboratory heating experiments we find that the calcites have different susceptibilities to solid state reordering reaction progress follows a first order rate law in both calcites but only after an initial period of non first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature we show that the apparent equilibrium temperature equations or closure temperature equations for carbonate clumped isotope reordering are analogous dodson s equations for first order loss of daughter isotopes for each calcite the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of 5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years however because the calcites have different susceptibilities to reordering each calcite defines its own cooling rate apparent equilibrium temperature relationship the cooling rates of carrara marble inferred from carbonate clumped isotope geospeedometry are 10 6 10 3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods cooling rates for 13c depleted calcites from the late neoproterozoic doushantou cap carbonates in south china are on the order of 102 104 degrees per annum consistent with rapid cooling following formation of these calcites by a short lived hydrothermal event bristow et al 2011 nature v 474 p 68 71 most of the uncertainty in these estimates relates to uncertainty in arrhenius parameters for different calcites thus while the carbonate clumped isotope geospeedometer shows promise for recording cooling rates in settings and lithologies where other geospeedometers may not be applicable the uncertainty in cooling rate will be large without independent knowledge of the reordering kinetics of each study material thus the full potential of the method will only be realized if reordering kinetics can be accurately determined for each study material or predicted on the basis of mineral composition texture or other observable parameters

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

hydrocarbon bearing fluid inclusions in fluorite associated with the windy knoll bitumen deposit uk abstract hydrocarbon bearing fluid inclusions in fluorite associated with an outcropping bitumen deposit at windy knoll derbyshire have been analysed in situ using a combination of microthermometry fourier transform infrared ftir microspectrometry and ultraviolet uv microscopy the inclusions in these samples can be considered as a series with two endmembers aqueous inclusions containing a low density vapour phase and inclusions containing liquid oil with no detectable aqueous phase the majority of the inclusions are mixed types containing both aqueous and liquid hydrocarbon phases although microthermometry distinguishes at least two different aqueous fluids with varying homogenization temperatures and salinities the oil fraction is cogenetic and trapped together with just one fluid a low salinity low calcium brine with an average homogenization temperature of 134 c the majority of the liquid hydrocarbon bearing inclusions fluoresce bright blue under uv illumination with peaks around 475 nm characteristic of paraffinic oils the ftir spectra of these inclusions are dominated by peaks assigned to aliphatic c h bonding however inclusions have also been found which display a fluorescence typical of the red shift associated with less mature oils the ftir spectra display peaks assigned to c o c o and o ch2 bonding this study presents new data on the in situ analysis of hydrocarbon bearing fluid inclusions from this important area of natural petroleum seepage and ore mineralization the results suggest a direct link between the fluid inclusion populations the outcropping bitumens and fluorite deposition

tracing migration pathways by integrated geological geophysical and geochemical data a case study from the jx1 1 oil field bohai bay basin china tracing petroleum migration pathways is essential for predicting petroleum occurrence and reducing exploration risks associated with hydrocarbon charge but a difficult task because of rapid lateral and vertical facies changes in lacustrine basins an integration of geological geophysical and geochemical analysis is employed to investigate the origin of crude oil the carrier bed architecture and migration pathways from source to trap in the jx1 1 oil field liaodong bay subbasin bohai bay basin detailed geochemical studies suggest that three potential source rock intervals and exist in the liaodong bay subbasin and crude oil in the jx1 1 field was derived from the and source rocks the carrier beds from and source rocks to the trap were characterized using geophysical data the fan delta sandstone in the member has an immediate contact with source rock and served as dominant conduit for the expulsion and migration of oil generated from source rock the braided delta sandstones overlying the source rock served as dominant conduit for sourced oil the focusing of petroleum migration pathways and the merge of migration pathways in and sandstones account for the accumulation of the jx1 1 field and the mixing of and sourced oil in the field this study suggests that the distribution of permeable sandstones and their stratigraphic contact with the source rocks are key for petroleum migration and occurrence and integration of geophysical geological and geochemical studies provide an effective way to trace petroleum migration pathways

present jurassic petroleum charge facing paleozoic biodegraded oil geochemical challenges and potential upsides embla field north sea the embla field located in the greater ekofisk area of the norwegian part of the southern north sea has been producing oil and gas since the early 1990s the wells on the crest are the best and most continuous producers whereas the wells on the flanks are only good producers over limited periods after pressure buildup the reason for the poorer production from the flanks is reduced permeability caused by the presence of bitumen a nonmovable biodegraded oil that fills the pore space this oil is shown to be of paleozoic age and is suggested to have charged the embla field at the end of the triassic the structure was uplifted and eroded during the jurassic and the paleozoic oil accumulation became biodegraded on the oil water contact the crest of the structure is believed to have been protected from biodegradation until the seal was eroded which resulted in the escape of the oil and the biodegradation of the residual oil subsidence during the cretaceous the formation of a new seal and the upper jurassic source rock intervals reaching oil window maturity resulted in the structure being recharged partly contradicting maturity estimates based on various biomarker ratios suggest that the analyzed oils represent different mixing ratios between the two oil generations the change in light oil composition observed between the drill stem tests sampled approximately 20 yr ago and the presently produced oil suggests that the embla field currently is receiving jurassic sourced oil

constraints on paleofluid sources using the clumped isotope thermometry of carbonate veins from the safod san andreas fault observatory at depth borehole abstract the san andreas fault observatory at depth safod near parkfield california is a borehole drilled through two active deforming zones of the san andreas fault the southwest deforming zone sdz and the central deforming zone cdz these zones accommodate displacement by seismic slip and aseismic creep elevated fluid pressures and fluid rock interactions have been proposed to explain the low apparent strength and aseismic creep observed but the origin of the fluids and existence of high fluid pressures remains uncertain we use clumped isotope thermometry and 18o 13c compositions of calcite in veins to constrain the origin of paleofluids and compare these results to the isotopic composition of modern day pore fluids from the safod borehole and nearby areas we observe that 1 calcite vein temperatures vary from 81 to 134 c which overlaps the current ambient borehole temperatures of 110 115 c at sampled depths 2 vein calcite is not in carbon isotope equilibrium with modern day pore fluids 3 the 18o values of paleofluids close to the sdz and cdz calculated from vein 18o and temperature data are not in equilibrium with local modern day pore waters but approach equilibrium with modern pore waters far from these zones and 4 syntectonic vein calcite is only in c and o isotopic equilibrium with their host rocks within the sdz and cdz spatial patterns of 18o and 13c show little evidence for across fault fluid flow clumped isotope temperatures are consistent with locally derived fluid sources but not with continuous or episodic replenishment of fluids from shallow sedimentary brines or deep fluid sources our findings are compatible with flow of meteoric fluids from the southwestern damage zone into the sdz and cdz which would have favored the formation of weak phyllosilicates and contributed to the present day weakness of the two actively deforming zones

distribution controlling factors and oil source correlation of biodegraded oils in the bohai offshore area bohai bay basin china the vast majority of discovered oils in the bohai offshore area have undergone biodegradation varying from 1 to 9 on the pm scale a scale to rank the level of biodegradation proposed by peters and moldowan 1993 the distribution and biodegradation extent of all discovered oils in the bohai offshore area were investigated systematically using geologic and geochemical data to reveal controlling factors of varying levels of biodegraded oils based on the analysis on environment and maternal significances and the resistance to degradation of biomarkers the biomarker parameter assemblage that is suitable for the oil source correlation of severely biodegraded oils higher than pm 6 in the bohai offshore area was determined spatial distribution and biodegradation extent are mainly controlled by current burial depth the duration of biodegradation the area of the oil water contact owc and a late strike slip movement of the tanlu fault almost all biodegraded oils are found in shallow reservoirs above 2000 m the longer the oils are present in these reservoirs or the larger the area of owc the reservoirs show the greater the extent of biodegradation will be the late strong strike slip movement of the tanlu fault may have significantly enhanced the biodegradation extent of several oils in fields located in the tanlu fault zone by introducing oxygenated freshwater from the surface or near surface and creating a more suitable environment for biodegradation c19 tricyclic terpane c23 tricyclic terpane c19 c23 tt c24 tetracyclic c26 tricyclic terpane c24 tet c26 tt and gammacerane c24 tetracyclic gam c24 tet do not seem to be influenced by biodegradation and show obvious differences between the three different source rock intervals such a biomarker parameter assemblage can be used successfully to determined the origin of severely biodegraded oils higher than pm 6 by correlating with extracts of possible source rocks in the bohai offshore area

the impact of severe biodegradation on the molecular and stable c h n s isotopic compositions of oils in the alberta basin canada abstract although the effects of biodegradation on the composition and physical properties of crude oil have been well studied effects of in reservoir petroleum biodegradation on molecular and isotopic compositions of crude oils are not yet clearly understood the alberta basin in western canada is one of the world s largest petroleum accumulations and constitutes an ideal example of a natural suite of sequentially biodegraded oils the basin hosts moderately to severely biodegraded petroleum regionally distributed and in single more or less continuous oil columns in this study a series of oil samples from the alberta heavy oil and oil sands provinces with varying degrees of biodegradation were analyzed to assess the impact of progressive biodegradation on the molecular and c h n and s isotopic compositions of oils the results of the molecular characterization of the hydrocarbon fraction of the studied oils show that the oils have suffered biodegradation levels from 2 to 10 toward the alberta saskatchewan border on the peters and moldowan scale of biodegradation abbreviated pm 2 to pm 10 and from tens to hundreds on the manco scale within single reservoirs increasing biodegradation was observed from top to bottom of the oil columns at all sites studied the whole oil stable isotopic compositions of the samples varied in the ranges 13 c 31 2 to 29 0 2 h 147 to 133 15 n 0 3 4 7 and 34 s 0 4 6 4 the maximum differences between values of samples within single oil columns were 13 c 1 4 2 h 7 15 n 1 7 and 34 s 1 0 regional variations in the isotopic compositions of oil samples from different wells averaged values from top to bottom were 1 2 for 13 c 12 for 2 h 4 1 for 15 n and 5 5 for 34 s and hence generally significantly larger variations were seen than variations observed within single oil columns especially for n and s it appears that even severe levels of biodegradation do not cause observable systematic variations in carbon nitrogen or sulfur isotope composition of whole oils this indicates that sulfur and nitrogen isotopic compositions may be used in very degraded oils as indicators for oil charge from different source rock facies

hydrothermal fluid origins in a fluorite rich mississippi valley type district combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the south pennine ore field united kingdom the south pennine peak district ore field united kingdom is host to several fluorite rich mississippi valley type deposits and was chosen for study as an analogue to the illinois kentucky fluorspar district united states the study was undertaken to test the idea that the large scale carbonate dissolution and fluorite rich mineralogy characteristic of both districts may require a magmatic source of hf the data also provide constraints for water rock interactions and potential fluid sources relevant to the local geology of the south pennine ore field samples were studied from two of the largest and most economically important deposits within the south pennine ore field the hucklow edge and dirtlow rakes in vacuo crushing of irradiated calcite samples released inclusion fluids that were analyzed for noble gas isotopes ar ar kr and the halogens cl br i this was achieved simultaneously by noble gas mass spectrometry ar ar methodology and was combined with fluid inclusion thermometric salinity data to determine noble gas concentrations in addition he isotope analyses were obtained from unirradiated fluorite the he he ratio of the pennine ore fluids 0 1 ra where ra atmospheric he he ratio of 1 4 10 is significantly lower than the maximum value recorded in the illinois kentucky fluorspar district 0 35 ra kendrick et al 2002 this volume indicating a crustal fluid source and supporting existing basinal brine models the low ar ar ratios with most 50 to 60 percent halite dissolution water br cl mol ratio 0 57 0 92 10 the salinity of fluids included in the main stage of the hucklow edge mineralization avg of 22 wt nacl equiv places an upper limit on the extent of meteoric recharge at 15 vol percent a secondary vein present at hucklow edge has a lower salinity of 40 m y a time scale compatible with models in which fluids were derived from small local basins such as the widmerpool and edale gulfs

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

geochemical characterisation and genetic origin of oils and condensates in the south viking graben norway abstract geochemical analysis of oil and condensate samples from all major fields and discoveries in the norwegian south viking graben as well as source rock extracts of upper and middle jurassic source horizons was carried out to characterise reservoired hydrocarbons and establish genetic relationships the south viking graben is in a mature phase of exploration and this study aims at unravelling regional trends to improve predictions in exploration and will show the significance of the play models in the area seven hydrocarbon families have been identified based on interpretation of molecular and isotopic characteristics and multivariate analysis of biomarker data these families can be linked to three source horizons three families originate from different facies of the draupne formation and are characterised by pr ph ratios below 2 dominance of c 27 regular steranes over the c 29 homologues and carbon isotopic values for saturate and aromatic fraction lighter than 28 and 27 respectively the upper jurassic heather formation and the middle jurassic vestland group each source one group of hydrocarbons typical for heather sourced hydrocarbons are elevated pr ph ratios between 2 35 and 3 08 low ratios of c 27 c 29 regular steranes and average isotopic values of 28 4 13 c sat and 26 8 13 c aro hydrocarbons from a middle jurassic source are characterised by very heavy isotopic composition highest pr ph ratios of the data set and dominance of c 29 regular steranes over the c 27 homologues among other factors the two remaining families represent mixtures from upper and middle jurassic sources and are mainly encountered in the greater sleipner area the available data in this study allowed characterisation of 84 of the recoverable oil resources which proved that the main source rock in the area is the upper jurassic draupne formation the play concept including a draupne source and tertiary reservoir proves to be most prolific with 239 10 6 s m 3 of recoverable oil equalling 88 of the total characterised oil resources oils in these tertiary reservoirs are however likely to be affected by biodegradation based on the available data the zone of biodegradation in the south viking graben appears to be limited to depths above 2140 m and temperatures below 70 c

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

circum arctic petroleum systems identified using decision tree chemometrics source and age related biomarker and isotopic data were measured for more than 1000 crude oil samples from wells and seeps collected above approximately 55n latitude a unique multitiered chemometric multivariate statistical decision tree was created that allowed automated classification of 31 genetically distinct circum arctic oil families based on a training set of 622 oil samples the method which we call decision tree chemometrics uses principal components analysis and multiple tiers of k nearest neighbor and simca soft independent modeling of class analogy models to classify and assign confidence limits for newly acquired oil samples and source rock extracts geochemical data for each oil sample were also used to infer the age lithology organic matter input depositional environment and identity of its source rock these results demonstrate the value of large petroleum databases where all samples were analyzed using the same procedures and instrumentation

calcite precipitation in synthetic veins implications for the time and fluid volume necessary for vein filling although calcite is a common vein filling mineral in rocks there has been little understanding of the kinetics of vein filling that gives a quantitative estimation of the fluid volume and time needed for calcite vein formation in subsurface fracture systems a new experimental system capable of simulating calcite precipitation in veins was used to determine the influences of flow velocity and initial solution saturation state on the quantitative precipitation pattern of calcite in synthetic veins results are in relatively good agreement with the model predictions use of a mn2 tracer indicated that even at low concentrations manganese can have a substantial effect on the morphology of the calcite precipitate our model predicts that an extremely large volume of fluid is required to produce calcite veins in nature typically 105 to 106 for a fluid calcite volume ratio for formation of thin short veins the model also predicts the time necessary for vein filling is thousands to millions of years and is highly variable depending on factors such as fluid saturation state flow velocity vein dimension and the precipitation kinetics that can differ under subsurface conditions

thermal comparison of mississippi valley type lead zinc deposits and their host rocks using fluid inclusion and conodont color alteration index data fifteen north american mississippi valley type districts distributed from the arctic archipelago to arkansas and in host rocks ranging in age from late cambrian to early carboniferous were selected for abroad test survey of mississippi valley type district thermal histories for each district in which data were collected histograms of homogenization temperatures for the ore minerals were compared with the temperature range of the corresponding host rocks as indicated by color alteration index cai determinations on conodonts in the host rock carbonates although a special effort was made to collect conodonts from the upper cambrian bonneterre formation host rock to the southeast missouri district all samples were devoid of conodonts thus only 14 districts were used in the final analysis comparison of fluid inclusion homogenization temperatures in main stage ore minerals with color alteration index determined host rock temperatures reveals that a majority of mississippi valley type districts pine point newfoundland zinc mascot jefferson city copper ridge sweetwater central missouri northern arkansas and tri state are representative of group 1 i e they are in thermal equilibrium with their host rocks insofar as could be determined by the color alteration index method ore minerals in group 2 districts upper mississippi valley polaris and central tennessee are significantly hotter than surrounding host rocks and as such define a positive thermal anomaly host rocks to the austinville ivanhoe northern newfoundland and robb lake deposits group 3 revealed the highest color alteration index values of north american mississippi valley type districts with host rock temperatures greatly exceeding ore mineral fluid inclusion temperatures negative thermal anomaly with respect to major tectonic elements of north america group 3 deposits cool ore in hot rocks are positioned within orogenic belts but on the continental side some group 1 deposits ore temperature host rock temperature are well within the continental interior but others are adjacent to orogenic belts on the continental side group 2 deposits hot ore in cool rocks are all within the continental interior current hypotheses regarding the formation of mississippi valley type deposits and simultaneous heating of their host rocks invoke the migration of hot brines set into motion craton ward by the hydraulic gradient produced by orogenic uplift at the craton edge once the ore bearing fluids entered the foreland carbonate platforms they traveled through sedimentary aquifers of the continental interior raising the temperature of the thinly covered carbonate rocks the fluids left as evidence of their passage elevated color alteration index values and group 1 mississippi valley type deposits distributed with decreasing homogenization temperatures away from the orogenic front the correspondence between host rock and ore temperatures suggests that group 1 deposits were deposited essentially within their own aquifers group 2 deposits were formed when the same or genetically similar fluids rose from the regional aquifer s into structurally controlled conduits in the continental interior possibly developed as a result of synorogenic doming and arching this upward channeling of the fluids resulted in rapid and localized fluid flow which precluded or at least inhibited wide spread heating of the host rocks by ore fluids consequently color alteration index values in group 2 districts record only maximum burial depths of the host rocks and bear little relation to temperatures of the ore fluids although the cause of the unusually high color alteration index values 4 5 of group 3 districts is not fully understood it is noted that these districts occur near the extreme outward edge of foreland platforms near or within the leading margins of orogenic belts whether these group 3 host rocks were heated by simple tectonic burial or by passage of heated fluids under shallower conditions is not known

the relationship between bitumens and mineralization in the south pennine orefield central england like many examples of mississippi valley type mineralization the south pennine orefield is well known for the occurrence of hydrocarbons within hydrothermal mineral veins bitumens from this area along with oils from the east midlands have been characterized using standard organic geochemical techniques and compared with potential source rocks lower namurian mudstones from the widmerpool gulf and the gainsborough and goyt troughs were rejected as possible sources for the bitumens and oils on the grounds of lack of sufficient thermal maturity and or essential biomarker correlation lower namurian mudstones with type ii kerogen from the edale gulf are proposed to offer a likely hydrocarbon source for the area with a minor more localized contribution from organic rich type ii mudstone partings within the dinantian limestones simple geochemical models consistent with recent sequence stratigraphic interpretation suggest a late carboniferous age for hydrocarbon generation where geothermal gradients were slightly higher c 50 c km 1 than the present day microthermometric analysis of fluid inclusions from fluorite and calcite allowed three fluid types to be distinguished one na ca cl bearing fluid was discerned to be dominant throughout the orefield being of low temperature uncorrected t h 70 110 c and high salinity c 20equiv wt nacl a second high salinity na ca cl fluid uncorrected t h 70 120 c c 24equiv wt nacl distinguished from the first by varying na ca contents was observed in the westernmost extremities of the orefield a third nacl bearing fluid of higher temperature t h 100 145 c and lower salinity 4 wt nacl was detected in the northernmost part of the orefield hydrocarbon bearing inclusions were not observed in any of the three fluids in this study sulphur isotopic analyses performed on a selection of sulphides sulphates and bitumens to gauge the role of organic matter in sulphate reduction reactions proved inconclusive the mineralization is thought to have occurred as several events that in the north is thought to be derived from the dewatering of the edale gulf towards the end of the carboniferous whilst other mineralization events occurred from the early permian onwards with the ore fluids having more distal sources predominantly from the east with a minor input from the west the main phases of hydrocarbon generation and mineralization appear to be unrelated

thermal history and tectonic subsidence of the bohai basin northern china a cenozoic rifted and local pull apart basin the bohai basin is a part of the larger bohai bay basin a cenozoic rifted intraplate basin heat flow measurements show that the bohai basin is characterized by present day heat flow varying between 53 and 74 mw m 2 with a mean of 63 mw m 2 however thermal history analyses derived from vitrinite reflectance vr and apatite fission track aft data indicate that tertiary cooling took place following a period of much higher paleo heat flow 70 90 mw m 2 prior to 25 million years to the present furthermore tectonic subsidence analysis reveals that the bohai basin experienced episodic sub rifting processes from the eocene to the end of the oligocene the post rift thermal subsidence was superimposed by intensified subsidence from the late miocene 12 million years in the bozhong depression and from the early quaternary 2 4 million years in the east liao bay indicating a rejuvenation of sedimentation related likely to transpressional structures developed locally on strike slip faults the present results indicate that there is good agreement between the reconstructed thermal history and the timing of the tectonic subsidence stages within the bohai basin the bohai basin is an early cenozoic rifted and local pull apart sub basin of the larger bohai bay basin 2001 elsevier science b v all rights reserved

comparison of clumped isotope signatures of dolomite cements to fluid inclusion thermometry in the temperature range of 73 176 c abstract widespread application of the novel clumped isotope paleothermometer 47 using dolomite samples from shallow crustal settings has been hindered by a lack of adequate constraints on clumped isotope systematics in dolomites that formed at temperatures greater than 50 c consequently many high temperature applications involving diagenetic dolomites have required an assumption that the relationship between temperature and 47 in diagenetic dolomite resembles the theoretical temperature dependence for calcite here we present 47 results from dolomite cements for which precipitation temperatures were determined independently using fluid inclusion microthermometry we compare a rock based calibration for samples from the temperature range of 73 to 176 c to previously published laboratory derived calibrations for synthetic calcites this novel combination of approaches yields results that are broadly consistent with results reported from controlled laboratory experiments providing an important confirmation of the utility of clumped isotopes in real world systems our results suggest that the 47 of dolomite cements may provide key information in the reconstruction of burial and thermal histories and also in the recognition of potential petroleum reservoirs

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

relation of sequence stratigraphy to modern sedimentary environments one method of testing the concept of sequence stratigraphy is to compare it to quaternary sediments in which chronology stratigraphic relations and facies geometry are more clearly understood than in older rocks rapid deposition rates during quaternary glacial eustatic cycles in large deltaic depocenters generate sequences comparable to those in the ancient stratigraphic record in the northern gulf of mexico the late wisconsinan holocene mississippi river has deposited a type 1 sequence that includes lowstand transgressive and high stand systems tracts characteristics of modern mississippi river sedimentary environments support the methodology used in sequence analysis but the short time taken for sequence generation here raises important questions about sequence time scales correlation and driving mechanisms

control of hydrocarbon seepage intensity on level of biodegradation in sea bottom sediments offshore surface geochemical surveys which target the surface expression of potential migration pathways for sampling such as fault scarps or diapiric features have become a commonly applied approach in the petroleum industry results of such surveys help to reduce risk on key exploration play elements and are used to evaluate prospects and to predict hydrocarbon phase and expected properties based on geochemical surveys conducted by exxonmobil in many basins worldwide there is an interrelation of the seep intensity concentration and level of biodegradation results from offshore west africa where many active macroseeps show moderate to severe biodegradation and a frontier basin offshore united kingdom rockall trough where active microseeps show no evidence of biodegradation are compared the specific biochemical controls on the difference in biodegradation proneness are not known although it appears that a certain threshold of oil concentration is needed to sustain an active bacterial community or to exceed clay adsorption capacities that may protect microseeps from biodegradation it is notable that the 25 norhopane series often considered an indication of severe biodegradation in reservoir oils has not been recognized in even ultra severely biodegraded seeps this suggests that different biodegradation pathways may be followed in marine surface seeps versus those in subsurface hydrocarbon accumulations a likely scenario in light of the fact that physiologically diverse bacterial communities are prevalent under different physiochemical conditions

reducing uncertainties in carbonate clumped isotope analysis through consistent carbonate based standardization about a decade after its introduction the field of carbonate clumped isotope thermometry is rapidly expanding because of the large number of possible applications and its potential to solve long standing questions in earth sciences major factors limiting the application of this method are the very high analytical precision required for meaningful interpretations the relatively complex sample preparation procedures and the mass spectrometric corrections needed in this paper we first briefly review the evolution of the analytical and standardization procedures and discuss the major remaining sources of uncertainty we propose that the use of carbonate standards to project the results to the carbon dioxide equilibrium scale can improve interlaboratory data comparability and help to solve long standing discrepancies between laboratories and temperature calibrations the use of carbonates reduces uncertainties related to gas preparation and cleaning procedures and ensures equal treatment of samples and standards we present a set of carbonate standards of diverse composition discuss how they can be used to correct for mass spectrometric biases and demonstrate that their use significantly improves the comparability among four laboratories we propose that the use of these standards or of a similar set of carbonate standards will improve the comparability of data across laboratories

the controls on the composition of biodegraded oils in the deep subsurface part 1 biodegradation rates in petroleum reservoirs abstract biodegradation rates in oilfields have been assessed conservatively using whole oil column minimum rate estimates diffusion controlled oil column compositional gradient modelling and mixed oil kinetic models biodegradation rate constants first order are around 10 6 10 7 yr 1 for hydrocarbons in the degradation zones these corresponding well with zero order field wide minimum rate estimates of about 10 8 kg hydrocarbons kg oil year for the whole oil column with biodegradation induction times of around 1 2 ma to perturb an entire oil column for light oil reservoirs and 10 20 ma for heavy oil reservoir degradation the results indicate that where we see continuous gradients in the oil columns degradation must have been occurring episodically for many millions of years to remove the n alkanes from an oil i e about 10 of an oil around ca 15 ma is needed for a heavy oil ca 5 ma for a light n sea oil the timescales of oilfield degradation and filling are thus very similar and consequently the degree of biodegradation will be substantially controlled by oilfield charge history assessment of mixed degraded non degraded oil occurrence provides an independent confirmation that these rates are realistic and that timescales of degradation and field charging are similar the maximum effective rate constant of degradation ultimately controlled by the limiting effect of diffusion of alkanes to the oil water contact owc ca 10 4 yr 1 for a 130 m thick oil column first order rate constant is well above the estimated rate constants indicating oil biodegradation rate is not limited by electron donor supply i e hydrocarbons but by supply of nutrients or oxidants this suggests that diffusive transport of nutrients and electron acceptors in the aquifer to the site of biodegradation may be adequate to maintain the low rate biosphere

the malines cambrian carbonate shale hosted pb zn deposit france thermometric and isotopic h o evidence for pulsating hydrothermal mineralization microthermometric stable isotope d h 18o 16o and raman spectroscopic data are given for four different mineralization events located beneath a triassic unconformity these events include the pb zn bearing kii mineralization which fills geodes and fractures in the main karstic mineralization ki and the f mineralization which fills fractures in the cambrian carbonates and shales post ki pre kii and f mineralization fluids were hot 150 c moderately saline 10 equiv wt nacl and precipitated red dolomite subsequently equally hot but more saline 20 equiv wt nacl fluids deposited white dolomite and then sphalerite of the f mineralization they were followed by another generation of dolomite at about 70 c from fluids with about 15 equiv wt nacl and even later barites 165 c 10 equiv wt nacl variation in the homogenization temperature with salinity for the different dolomite generations suggests that the hot saline fluids were repeatedly diluted by a cooler less saline fluid the fluids are interpreted to be of formation water origin having possibly developed in the deep levels of the rhone basins to the southeast which was at least 3 km thick at the time of mineralization post hetangian the inferred metal bearing hot brines were probably episodically expulsed during the dewatering of the basin depositing their mineralization in the more permeable fault and karstic zones associated with the uplift of the st bresson horst cold surface waters probably invaded the mineralized zones between the pulses of hydrothermal solutions this hydrothermal model with the introduction of sulfides can account for the precipitation and dissolution textures associated with the hydrothermal mineralizations

the origin of carbonate cements in the hildasay reservoir cambo field faroe shetland basin clumped isotopic analysis and implications for reservoir performance abstract the early eocene paralic sandstones of the hildasay member of the flett formation form the major oil bearing reservoir in the cambo field located in the faroe shetland basin the sandstones locally contain calcite cemented intervals that vary in thickness from decimetre to over 1 m a calcite cemented interval from well 204 10a 5 has been analysed petrographically and using clumped isotopes to determine its mode of formation and potential lateral extent petrographic analysis shows the cemented interval to consist of ferroan calcite with a consistent dull red cathodoluminescence suggesting a single phase of precipitation the centre of the cemented interval comprises a finer grained unit with detrital kerogen and early sphaerosiderite while the rest comprises homogeneous porosity occluding ferroan calcite the early sphaerosiderite in the centre is replaced by ferroan calcite with a high 13 carbon isotopic signature 13 cvpdb 7 53 suggesting that it formed during anaerobic methanogenesis or fermentation samples from the intermediate zone have a lower 13 carbon isotopic composition 13 cvpdb 0 72 to 3 68 in comparison the outer margin of the cemented unit has an even lower 13 carbon isotopic signature 13 cvpdb 15 5 to 15 9 more typical of a strong aerobic oxidation source the oxygen isotopic signature of the cements is similar 18 ovpdb 10 9 to 12 2 analysis of the clumped isotopes suggest that the ferroan calcite formed at 40 50 c from pore waters that were predominantly meteoric in origin 18 ovsmow 4 8 to 5 7 burial history modelling would suggest that the cements formed at a depth of 500 1000 m meteoric water was likely to have been introduced during the formation of the mid lutetian unconformity 45mya approximately 10 mya after the sandstones were deposited the model proposed is that ferroan calcite precipitation was initiated in the fine lag deposits that contained the kerogen and sphaerosiderite and then grew outwards if the model is correct the cemented units should be restricted to this facies and consequently of limited lateral extent consequently it is likely that the cemented intervals will have a limited impact upon the reservoir performance and are unlikely to act as major barriers to fluid flow

application of biological markers in the assessment of paleoenvironments of chinese non marine sediments abstract in this study we employ molecular organic geochemical data for 22 representative sediment samples from chinese non marine sedimentary basins in an attempt to characterize and assess the non marine depositonal paleoenvironments the samples investigated include oilshale shale mudstone and sodium sulphate rich sediments ranging in age from cretaceous to tertiary it is evidenced by geological and geochemical data that those sediments studied originate from lacustrine environments ranging from freshwater brackish fresh water to hypersaline the aliphatic fractions of the sediment extracts were analyzed by gc and gc ms and relative abundance of compounds and compound classes of normal acyclic and cyclic alkanes were measured from mass chromatograms the results reveal significant differences in the chemical features of the various sample groups which enable them to be characterized and identified in terms of source and or environment related parameters the diagnostic parameters that allow this assessment are the relative abundances of n alkanes acyclic isoprenoid alkanes and 4 methyl steranes hopane sterane ratio gammacerane and homohopane indexes etc in this study data interpretation was also assisted by pattern recognition through principal component analysis the results show that the sample groups of different environmental origin could be unambiguously distinguished on scores plot

molecular organic geochemistry of the tarim basin northwest china we conducted organic geochemical analyses on the largest suite of oils and source rock extracts from the tarim basin northwest china currently available statistical cluster analysis of the entire suite of tarim oils distinguishes at least seven genetic groups of oils the largest group of oils was collected from the tazhong and tabei uplifts and originated from marine middle upper ordovician anoxic marls that mark slope facies at the margins of structural uplifts two other genetic groups most likely originated from marine middle upper ordovician source rocks but of distinct facies with one an oxic shale rich source west of the bachu uplift and the other an anoxic shale source at tazhong

a practical biodegradation scale for use in reservoir geochemical studies of biodegraded oils existing scales widely used to describe the extent of biodegradation of petroleum have insufficient resolution to usefully characterize many heavy oil and bitumen occurrences including the volumetrically dominant heavily and severely biodegraded oil accumulations in the foreland basins of western canada and venezuela in these and other deposits existing classifications or descriptions of the biodegradation level may vary only slightly yet oil may vary in viscosity by orders of magnitude the manco biodegradation scale proposed here is based on integrating the extent of degradation of various members of compound classes not included in previous biodegradation scales they include alkyl aromatic and alkyl thiophenic compounds that show variable extent of alteration in samples degraded to uniform levels on standard scales but which may show variation in local degradation systematics related to biodegradation mechanisms and extent of oil mixing the manco scale uses a combination of a consideration of the extent of alteration within a compound class together with a consideration of biodegradation across a range of compound classes it can be reliably used as a basis for interpreting geochemical changes in heavily biodegraded oil suites and can also be used to differentiate biodegraded oil samples likely to be amenable to cold production from those requiring production strategies such as steam or chemical flooding as with other biodegradation scales the scale may also provide evidence for the influx of later higher quality oil into a reservoir fluid that had been previously biodegraded

cenozoic exhumation of the southern british isles rocks that crop out across southern britain were exhumed from depths of as much as 2 5 km during cenozoic time this has been widely attributed to paleocene regional uplift resulting from igneous underplating related to the iceland mantle plume our compilation of paleothermal and compaction data reveals spatial and temporal patterns of exhumation showing little correspondence with the postulated influence of underplating instead being dominated by kilometer scale variations across cenozoic compressional structures which in several basins are demonstrably of neogene age we propose that crustal compression due to plate boundary forces transmitted into the plate interior was the major cause of cenozoic uplift in southern britain witnessing a high strength crust in western europe

fluid expulsion from overpressured basins implications for pb zn mineralisation and dolomitisation of the east midlands platform northern england abstract our understanding of burial diagenesis within carbonates is often limited by poor constraints on available fluid volumes and geochemistry however regional stratigraphic and burial history data are often readily available using these data to develop numerical models which couple sedimentological and hydrological basin evolution we estimate the volumes and geochemistry of fluids that were available to drive dolomitisation and pb ore genesis within the carboniferous derbyshire platform of northern england current conceptual models of these processes invoke tectonic release of burial induced overpressure developed within adjacent dinantian basins as a drive for reactive fluid flow to the platform our simulations show that compaction driven flow may lead to a supply of fluids that is more complex in its temporal evolution than may be expected spatial variations in the rate of fluid expulsion from different sediments lead to a staggered delivery of fluids from different sources rapid fluid expulsion within deeper sediments leads to a downwards decreasing pressure gradient that subsequently draws down fluid from within overlying sediments thus early fluid supply to the platform is sourced from the deep basins while later fluid supply descends from above the platform as well as from the sides we suggest that such a flow development may have important implications for the relative timing and distribution of a sequence of diagenetic products within the platform this hypothesis is tested using volume estimates from our simulations we conclude that although this staggered fluid supply model may be applicable generically it appears that it is only valid for explaining mineralisation in the derbyshire platform fluid volumes supplied to the platform are insufficient to explain dolomitisation our simulations are supported by a sensitivity analysis that identifies that compaction driven flow in this system is strongly controlled by the rate of burial and sediment permeabilities within the compacting basins

geothermal regime and hydrocarbon kitchen evolution of the offshore bohai bay basin north china the offshore bohai bay basin located in the central bohai bay basin north china one of the most petroliferous basins in china in this article based on formation testing temperature drill stem tests and bottom hole temperature data 80 thermal gradient values at the depth interval of 0 to approximately 3000 m 9843 ft in the offshore bohai bay basin were obtained the basinwide average thermal gradient is 31 8 4 6c km based on the above thermal gradient data and the corresponding average weighted thermal conductivity data 80 measured terrestrial heat flow values were obtained these values range from 33 5 to 84 0 mw m2 with an average value of 60 8 8 7 mw m2 the heat flow and thermal gradient distribution in this region generally show higher values in the uplifts and lower ones in the sags a thermal history derived from vitrinite reflectance and apatite fission track data indicates that paleogene cooling occurred after a period of much higher paleogeothermal gradient 3854c km tectonic subsidence analysis reveals that the area experienced initial synrift subsidence during the paleogene followed by subsequent thermal subsidence since the neogene thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of petroleum source rock maturation the maturation and hydrocarbon expulsion histories of the paleogene shahejie 3 formation e2s3 which is the most important source rock in the offshore bohai bay basin are modeled results show that the shahejie 3 formation is in a high mature stage at the present day and the bozhong and qikou sags are the most important kitchens the huanghekou sag became the third most important hydrocarbon kitchen in the early neogene based on this hydrocarbon kitchen evolution oil and gas mainly accumulated after 12 ma the evolution of kitchen areas may provide new insights for the understanding of the oil and gas exploration potential of the offshore bohai bay basin

geochemical characteristics of tertiary saline lacustrine oils in the western qaidam basin northwest china abstract based on the systematic analyses of light hydrocarbon saturate aromatic fractions and c isotopes of over 40 oil samples along with related tertiary source rocks collected from the western qaidam basin the geochemical characteristics of the tertiary saline lacustrine oils in this region was investigated the oils are characterized by bimodal n alkane distributions with odd to even c11 c17 and even to odd c18 c28 predominance low pr ph mostly lower than 0 6 high concentration of gammacerane c35 hopane and methylated mttcs reflecting the high salinity and anoxic setting typical of a saline lacustrine depositional environment mango s k1 values in the saline oils are highly variable 0 99 1 63 and could be associated with the facies dependent parameters such as pr ph and gammacerane indexes compared with other tertiary oils the studied tertiary saline oils are marked by enhanced c28 sterane abundance 30 or more of c27 c29 homologues possibly derived from halophilic algae it is noted that the geochemical parameters of the oils in various oilfields exhibit regular spatial changes which are consistent with the depositional phase variations of the source rocks the oils have uncommon heavy c isotopic ratios 24 to 26 and a flat shape of the individual n alkane isotope profile and show isotopic characteristics similar to marine organic matter the appearance of oleanane and high 24 24 27 norcholestane ratios 0 57 0 87 in the saline oils and source rocks confirm a tertiary organic source

oil source correlation in the fulin basin shengli petroleum province east china the fulin basin is located within the giant shengli petroleum province in east china the source rock in the basin is mainly the lower part of the third member es3 of the eocene portion of the shahejie formation it is composed of organic rich dark mudstone and oil shale of lacustrine origin and contains good quality type i ii kerogen these strata reach the oil generative stage at ro 0 4 0 8 the first member es1 of the oligocene portion of the shahejie formation has excellent oil potential in the nearby gunan basin but is immature in the fulin basin and is not an effective source rock the oil and rock samples from both basins can be grouped into three major families based on biomarkers the first family shows low prph 0 3 and notable carotane typical of carbonate evaporite environments this family exists in es1 rocks and the related oils and is early mature 0 2 0 3 and s r s 0 10 0 20 the second family shows high prph 1 a low gammacerane index 0 2 and abundant 4 methyl steranes indicative of freshwater lacustrine conditions like those in es3 this family shows higher maturation 0 30 0 50 and s r s 0 35 0 55 and notable diasteranes the third family is transitional has source and maturity ratios between the above families and occurs in the es3 unit samples from the basin interior based on biomarker similarities between oils and rock extracts all oils in the fulin basin originated from es3 source rocks slight maturation differences indicate that these oils have been derived from different source areas no oil from es1 is found in the fulin basin suggesting es1 source rocks are too immature to generate commercial oil although the nearby gunan basin has much oil generated from es1 source rocks no migrated oil from es1 in this basin reached the kenli faulted zone because of intervening faults which disrupt migration

an experimentally verified model for calcite precipitation in veins calcite is commonly found as a vein filling mineral in rocks however the factors controlling its deposition are complex and not well understood in quantitative terms in order to advance our understanding of the processes involved we have refined the model for calcium carbonate mass transport in subsurface carbonate rocks of morse and mackenzie 1993 and developed a new experimental technique to test it this technique uses a flow through reactor that simulates a vein opening agreement was observed between model predictions and experimental observations for the deposition of calcite in synthetic veins the influences of surface area to solution volume ratio solution saturation state with respect to calcite and flow velocity were well predicted by the model the model predicts that in order to have a fairly uniform deposition of calcite within a vein solution flow must be quite rapid tens to thousands of cm h 1 or the solution must be only slightly supersaturated with respect to calcite a low degree of solution supersaturation demands what may be unreasonably large volumes of solution flow to achieve vein filling for the vein configuration we have studied

seismic reflection imaging of a major strike slip fault zone in a rift system paleogene structure and evolution of the tan lu fault system liaodong bay bohai offshore china the tan lu fault system in the liaodong bay bohai offshore china affords an exceptional opportunity to document the structural features of a major strike slip fault using two and three dimensional seismic reflection data as well as evolution of a strike slip fault developed coeval with a rift system the fault zone displays a relatively straight throughgoing trace longitudinally bisecting the rift valley it consists of positive and negative flower structures and en echelon folds in the south bay and three parallel flower structure systems northward the middle fault bifurcates northward into two semiparallel vertical fault strands to the north the west strand bends clockwise and merges with the east strand the stepping pattern and orientation of en echelon structures indicate right lateral sense and about n10 35e azimuth of slip the fault apparently accrued about 30 40 km 20 25 mi of post early eocene slip based on the current distribution of deformation zones and depocenters tan lu fault segments with clockwise and counterclockwise orientation relative to the regional slip direction are characterized by divergent and convergent structures i e restraining and releasing bends respectively waning of rifting eliminated the cause of a major restraining bend putting an end to development of associated convergent structures in the south bay area near the central north bay deformation occurred along major normal faults related to the basin rifting although a prominent feature reflecting regional strain partitioning the tan lu fault apparently was not a major factor in the paleogene opening of the liaodong bay basin and the larger north china rift basin

clumped isotope geochemistry clumped isotope geochemistry is concerned with the state of ordering of rare isotopes within natural materials that is it examines the extent to which heavy isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim

self ordering and complexity in epizonal mineral deposits epizonal base and precious metal deposits makeup a range of familiar deposit styles including porphyry copper gold epithermal veins and stockworks carbonate replacement deposits and polymetallic volcanic rock hosted vhms deposits they occur along convergent plate margins and are invariably associated directly with active faults and volcanism they are complex in form variable in their characteristics at all scales and highly localized in the earth s crust more than a century of detailed research has provided an extensive base of obser vational data characterizing these deposits from their regional setting to the fluid and isotope chemistry of mineral deposition this has led to a broad understanding of the large scale hydrothermal systems within which they form low salinity vapor released by magma crystallization and dispersed into vigorously convecting ground water systems is recognized as a principal source of metals and the gases that control redox conditions within systems the temperature and pressure of the ambient fluid anywhere within these systems is close to its vapor liquid phase boundary and mineral deposition is a consequence of short timescale perturbations generated by localized release of crustal stress however a review of occurrence data raises questions about ore formation that are not addressed by traditional genetic models for example what are the origins of banding in epithermal veins and what controls the frequency of oscillatory lamina tion what controls where the phenomenon of mineralization occurs and why are some porphyry deposits for example so much larger than others the distinctive self organized characteristics of epizonal deposits are shown to be the result of repetitive coupling of fracture dilation consequent on brittle failure phase separation boiling and heat transfer between fluid and host rock process cou pling substantially increases solute concentrations and triggers fast far from equilib rium depositional processes since these coupled processes lead to localized transient changes in fluid characteristics paragenetic isotope and fluid inclusion data relate to conditions at the site of deposition and only indirectly to the characteristics of the larger scale hydrothermal system and its longer term behavior the metal concentra 1 the us government has the right to retain a nonexclusive royalty free license in and to any copyright covering this paper