geochemical characteristics origins and model of lacustrine source rocks in the zhu 1 depression eastern pearl river mouth basin south china sea abstract variations in environmental and biological origins contributing to the heterogeneity of lacustrine source rocks can be illustrated in their diverse genetic facies the zhu 1 depression eastern pearl river mouth basin south china sea is characterized by two thick paleogene organic rich synrift units the wenchang and enping formations the integration of bulk geochemical and biomarker data with tectonic and sedimentary information provides the basis for a comprehensive assessment of the environmental and ecological changes through geologic time and their impact on the heterogeneity of these lacustrine source rocks both the wenchang and enping formations display wide variations in total organic carbon content and hydrogen index values as well as biomarker composition suggesting lateral and chronological changes in organic facies using gas chromatography mass spectrometry and hierarchical cluster analysis five genetic facies were identified within these two source horizons these facies represent different organic matter inputs and sedimentary and early diagenetic environments based on their distinctly different assemblages of 11 source dependent biomarker ratios four facies were distinguished in the wenchang formation and two facies were distinguished in the enping formation with one being common to both formations during the middle eocene the wenchang formation was deposited in a series of small deep lakes of laterally variable salinity acidity and biofacies during the deposition of the enping formation in the late eocene and early oligocene the previous lakes merged into fewer lakes with shallower depth and larger areal coverage with the biota becoming more uniform across the whole depression the coevolution of these lacustrine settings and their biota is closely associated with the development of the zhu 1 depression within which multiple separate sags produced by rapid mid eocene subsidence finally merged into a single depositional unit during slow subsidence in the late eocene and early oligocene accordingly an integrated model was established to provide an overview of the contrasting origins of lacustrine source rocks during the two paleogene epochs this model may have important implications for source rock prediction in the undrilled parts of the basins or for reference to source rock heterogeneity in other rift basins

green river laminites does the playa lake model really invalidate the stratified lake model proponents of the playa lake model have proposed deposition of most of the green river formation microlaminated carbonates including oil shales in lakes that were not perennially stratified meromictic however there is a variety of evidence favoring a meromictic depositional environment 1 close similarity of much of the lamination to varves in modern meromictic lakes 2 evidence that hydrologic events favoring development of meromixis chemical stratification occurred prior to deposition of major accumulations of oil shale 3 mutually exclusive distribution of fossil nekton especially fish and normal lacustrine benthos including mollusks and 4 analogy with a quaternary playa that became a meromictic lake following increased inflow the playa lake model is untenable for the typical fish bearing kerogen rich microlaminated sediments these laminites were probably deposited in a large ectogenic meromictic lake a chemically stratified lake that formed when increased fresh water inflow drowned a saline playa complex

upper permian lacustrine oil shales southern junggar basin northwest china upper permian organic rich lacustrine mudstones oil shales that crop out in the southern junggar basin rank among the richest and thickest petroleum source rock intervals in the world with maximum toc values reaching 34 and rock eval pyrolytic yields s 2 up to 200 kg hc t rock lacustrine sedimentary facies define an overall transgressive regressive cycle of approximately 2000 m gross thickness which includes approximately 800 m of source rocks averaging 4 1 toc and 26 2 kg hc t rock basinal facies comprise silicic organic rich laminated lacustrine mudstones and interbedded siltstones organic matter contained in the mudstones ranges in composition from type i to type iii basinal facies were deposited in a deep oxygen deficient stratified lake lake margi facies consist of nonlaminated siliciclastic mudstones rippled dolomitic siltstones and sandstones and minor limestones maximum toc values are approximately 6 desiccation cracks are common in the marginal facies but evaporite minerals are rare or absent biomarker correlation parameters measured from rock extracts exhibit significant stratigraphic variability but strongly support the hypothesis that upper permian lacustrine oil shales charge the giant karamay field in the northwestern junggar basin karamay oils are characterized by high relative abundances of beta carotane this characteristic is restricted to desiccated facies in the outcrop sections however we therefore propose that an abundance of beta carotane indicates elevated environmental salinities during deposition of the oil shales orographic precipitation induced by a paleo tian shan range may have provided fresh water to the southern areas of the basin while more evaporative conditions prevailed to the north outcrop oil seeps confirm that the outcrop sections have attained sufficient thermal maturity to generate oil t max values range from 431 to 451 degrees c vitrinite reflectances range from 0 73 to 0 88 and sterane isomerization ratios range from 0 30 to 0 48 20s 20s 20r matoil registered trademark computer modeling of burial history and thermal maturity of the outcrop sections indicates that approximately 4 5 km of triassic jurassic cover was needed to bring the oil shales to their current maturity the major phase of hydrocarbon generation in this area appears to have preceded the creation of traps by neogene thrusting which may account for the lack of discoveries in the southern junggar basin most of the oil discovered so far is trapped in structures which originated duri g the late paleozoic or mesozoic

oligocene miocene source rocks of the zhongcang basin implications for hydrocarbon potential differentiation between lake basins in central tibet abstract the oligocene miocene dingqinghu formation is widely distributed in lake basins of the bangong nujiang suture zone bnsz central tibet and has been reported as an important source rock layer however limited works have been conducted in the zhongcang basin to gain knowledge on hydrocarbon potential of this area and further investigate the organic matter om accumulation mechanisms of source rocks in the bnsz basins samples collected along two measured sections from the zhongcang basin were subjected to sedimentological organic geochemical and petrographic analyses sedimentological analyses indicate that all samples were deposited in prodeltic to deep lake environments total organic carbon toc values and pyrolysis data suggest a poor to fair hydrocarbon source potential of the middle dingqinghu formation with the exception of om rich samples locate in a marker bed of the upper part vitrinite reflectance ro values of the upper part and middle lower part samples range from 0 41 to 0 50 and 0 52 to 0 61 indicating immature and marginal mature stages respectively these maturity levels were also supported by specific maturity indices of sample extracts such as ratios of c31 22s 22s 22r homohopanes and c29 steranes bulk geochemistry maceral composition of kerogen and extract biomarkers demonstrate that om rich samples were deposited in fresh to brackish waters with type ii iii kerogen mainly derived from algae and higher plants while poor to fair samples have less higher plant contribution but relatively high bacterial content that probably originated from more saline environments the paleoclimate induced environmental reorganization is likely responsible for the differential om accumulation in the zhongcang basin relatively wet climates would facilitate primary productivity of the lake as well as development of swamps on the delta resulting in deposition of mixed terrestrial and aquatic om with higher toc whilst dry conditions would restrict the development of river systems and promote the establishment of saline environments causing decreased total om input but increased proportion of halophilic bacterial om in addition we summarized published data of the dingqinghu formation in the bnsz basins and preliminarily reconstructed paleogeography of central tibet two types of drainage patterns were confirmed in this area a long lived hierarchical drainage system is developed in the lunpola area while single lake systems were prevalent in other basins including the zhongcang basin the hierarchical drainage pattern could minimize clastic dilution effects during tectonic active and or relatively wet periods and prevent the establishment of hypersaline environments during the dry period the drainage center in this kind of hierarchical system has lower sedimentation accumulation rate and could receive much more aquatic om at any climatic conditions we argue that tectonic induced drainage organization primarily controlled the hydrocarbon potential differentiation between lake basins of central tibet

geochemical investigation of oils and source rocks from qianjiang depression of jianghan basin a terrigenous saline basin china abstract six oils and seven suspected source rocks from the jianghan saline basin in the central eastern part of china have been examined using a variety of geochemical techniques the results from this study show that oils from the third and fourth sections of the qianjiang formation eocene are derived from similar source materials but have a different source from the oils of xingouzui formation eocene in the same basin the oils of the xingouzui formation eocene are more mature and probably have a greater input of terrigenous source material and in all probability have migrated greater distances than the qianjiang oils oils from these sections are derived from an environment characterized as being extremely anoxic strongly reducing and highly saline the suspected source rocks examined in the study were from the qianjiang formation and were generally mature except for the shallowest sample the biomarker distributions in the suspected source rocks examined from the qianjiang formation were very different from those of the oils present in the same sections it is proposed that oils from the qianjiang formation have sources in addition to or exclusive of the suspected source rocks examined in this study

neoproterozoic paleozoic and mesozoic granitoid magmatism in the qinling orogen china constraints on orogenic process abstract the qinling orogen is one of the main orogenic belts in asia and is characterized by multi stage orogenic processes and the development of voluminous magmatic intrusions the results of zircon u pb dating indicate that granitoid magmatism in the qinling orogen mainly occurred in four distinct periods the neoproterozoic 979 711 ma paleozoic 507 400 ma and early 252 185 ma and late 158 100 ma mesozoic the neoproterozoic granitic magmatism in the qinling orogen is represented by strongly deformed s type granites emplaced at 979 911 ma weakly deformed i type granites at 894 815 ma and a type granites at 759 711 ma they can be interpreted as the products of respectively syn collisional post collisional and extensional setting in response to the assembly and breakup of the rodinia supercontinent the paleozoic magmatism can be temporally classified into three stages of 507 470 ma 460 422 ma and 415 400 ma they were genetically related to the subduction of the shangdan ocean and subsequent collision of the southern north china block and the south qinling belt the 507 470 ma magmatism is spatially and temporally related to ultrahigh pressure metamorphism in the studied area the 460 422 ma magmatism with an extensive development in the north qinling belt is characterized by i type granitoids and originated from the lower crust with the involvement of mantle derived magma in a collisional setting the magmatism with the formation age of 415 400 ma only occurred in the middle part of the north qinling belt and is dominated by i type granitoid intrusions and probably formed in the late stage of a collisional setting early mesozoic magmatism in the study area occurred between 252 and 185 ma with the cluster in 225 200 ma it took place predominantly in the western part of the south qinling belt the 250 240 ma i type granitoids are of small volume and show high sr y ratios and may have been formed in a continental arc setting related to subduction of the mianlue ocean between the south qinling belt and the south china block voluminous late stage 225 185 ma magmatism evolved from early i type to later i a type granitoids associated with contemporaneous lamprophyres representative of a transition from syn to post collisional setting in response to the collision between the north china and the south china blocks late mesozoic 158 100 ma granitoids located in the southern margin of the north china block and the eastern part of the north qinling belt are characterized by i type i to a type and a type granitoids that were emplaced in a post orogenic or intraplate setting the first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process these suggest that the tectonic evolution of the qinling orogen is very complicated

petroleum systems in the jiangling dangyang area jianghan basin china source related geochemical data define at least four petroleum systems in the jiangling dangyang area of the jianghan basin eocene paleocene anoxic evaporitic lacustrine source rocks generated most of the crude oils in the area eocene qianjiang rock from the sha 13 well 1322 m contains fast reacting sulfur rich type is organic matter and its extract is most similar to the sha 13 oil sand bitumen qianjiang reservoir lower eocene paleocene xingouzhui rocks from the xin 73 well 842 and 862 m contain slow reacting low sulfur type i organic matter and their extracts are most similar to the sha 26 oil sand bitumen eocene jinsha reservoir and the ling 2 sha 24 and tuo 3 oils xingouzhui reservoirs two unidentified middle triassic or older marine carbonate evaporite source rocks or different facies of the same source rock generated the daxiakou oil triassic jialingjiang formation outcrop xingshan county and the moderately biodegraded tianwan seep oil permian changxing outcrop chengxi county respectively one or more unidentified marine source rocks which could include the lower permian qixia or the upper sinian doushantuo formations generated the miaoshi and yanmenkuo seep oils permian qixia outcrops the jingshan seep oil ordovician baota outcrop probably is related to these oils but could represent another petroleum system different kinetics for hydrocarbon generation among eocene qianjiang and lower eocene paleocene xingouzhui formation source rocks and chemical differences among the related oils are caused by organic facies variations high salinity and low eh enhanced the preservation of oil prone organic matter in these lacustrine settings and facilitated incorporation of sulfur into the organic matter anoxia and the unusual presence of abundant sulfate as gypsum resulted in the microbial reduction of sulfate to sulfide and incorporation of this sulfur into the kerogen for example biomarkers show that source rock in the sha 13 well 1322 m was deposited under more saline lower eh conditions than that in the ling 80 well 1808 m although both are from the qianjiang formation the sha 13 rock sample is more organic rich 6 62 vs 1 27 wt toc and has a higher hydrogen index 794 vs 501 mg hc g toc and faster reaction kinetics than the ling 80 sample kerogen from the sha 13 sample is type is because it has a high hydrogen index and an atomic s c ratio 0 074 in the range of sulfur rich fast reacting kerogens of the monterey formation s c 0 040 organic rich lower jurassic coaly rocks from outcrops at daxiakou contain immature to mature gas prone organic matter that is not related to any oils in the study several organic rich upper sinian to permian samples could have been source rocks in the past but are now highly mature based on high tmax 464 540 c and estimated vitrinite reflectance ro values mass balance calculations were used to estimate the original toc toc c in these samples prior to maturation these samples could not be correlated with the oils using biomarkers because of high maturities and low extract yields however stable carbon isotope type curves suggest that the miaoshi yanmenkuo permian qixia formation and the jingshan ordovician baota formation seep oils originated from source rocks in the lower permian qixia 3 00 wt toc or upper sinian doushantuo formations 5 96 wt toc lack of triaromatic dinosteroids in the miaoshi and yanmenkuo seep oils supports but does not prove a permian source rock very negative stable carbon isotope ratios for kerogens from the lower cambrian shuijintuo formation 33 5 to 33 6 8 85 16 64 wt toc show that they are not related to any of the analyzed oils

multiple stage migration and accumulation of permian lacustrine mixed oils in the central junggar basin nw china abstract the permian lacustrine petroleum system in the central junggar basin northwest china has recently obtained exploration success these accumulations are characterized by mixed oils and multiple stage migration and accumulation this process however has not been well constrained limiting the understanding of the general laws of hydrocarbon migration and accumulation and making it difficult to define exploration strategies here we reconstruct this process mainly based on oil bearing fluid inclusion analyses including petrography homogenization temperature and sequential extraction inclusion petrography shows that petroleum inclusions dominantly display yellow fluorescence while intergranular free oils mostly display strong blue green fluorescence this implies that the reservoirs seem to have experienced at least two stages of hydrocarbon charge from different sources and or maturities the sources maturities are determined through reservoir sequential extraction analyses the free oils are mixed and sourced from the lower permian fengcheng formation p1f and the middle permian lower wuerhe formation p2w while the inclusion oils are also mixed and derived mainly from the p1f source both oils are characterized by moderate maturity homogenization temperature measurements of oil bearing fluid inclusions combined with reconstruction of reservoir burial and thermal history not only further verify multiple hydrocarbon charging events but also characterize the timing which indicates a three stage petroleum charging model during the first stage of the late triassic carboniferous reservoirs were charged by p1f sourced oils which were dysmigrated or remigrated to jurassic reservoirs during the second stage i e the early cretaceous in contrast the third stage from the late cretaceous represents another hydrocarbon charge event that is the primary oil accumulation sourced from the p2w rocks according to this model both primary and secondary oil accumulations contribute to the current region s exploration success and provide future exploration targets

early generation characteristics of a sulfur rich monterey kerogen this paper documents the critical role of organic sulfur in the early formation of bitumen and oil from a sulfur rich kerogen from the miocene monterey formation in california monterey kerogen commonly contains abundant chemically bound sulfur 8 14 wt which appears responsible for early low temperature generation of heavy sulfur rich petroleum due to the lower energy required to break carbon sulfur bonds compared to carbon carbon bonds hydrous pyrolysis was used to simulate the natural generation of petroleum from a sulfur rich type ii kerogen from the phosphatic member of the monterey shale the amount and distribution of sulfur in the kerogen bitumen and expelled oil generated at various temperatures indicate that 1 initial bitumen and oil generation is directly related to cleavage of weak sulfur linkages and 2 most of the expelled oil is formed by decomposition of bitumen and not directly from the kerogen finally comparison of hydrous pyrolysis results with other type ii kerogens suggests that the temperature of peak bitumen generation is inversely related to the heteroatom content primarily sulfur of the kerogen low temperature bitumen generation is an important exploration concept because kerogen rich in sulfur can generate producible oil at thermal maturities significantly below conventionally accepted values furthermore established relationships between thermal maturity sulfur content and other oil properties such as api gravity can be used to rank exploration prospects

influence of palaeoclimate and hydrothermal activity on organic matter accumulation in lacustrine black shales from the lower cretaceous bayingebi formation of the yin e basin china abstract the lacustrine black shales of the lower cretaceous bayingebi formation are an important hydrocarbon source rock in the yin e basin it is important to understand the mechanism of organic matter accumulation in these shales to reconstruct the palaeoenvironment and palaeoclimate in the early cretaceous in northwestern china and search for potential oil and gas resources based on petrological elemental geochemical and organic geochemistry analyses of typical field profile samples the influence of palaeoclimate and hydrothermal activity on organic matter accumulation in different sedimentary units unit i ii and iii is revealed unit ii has the highest total organic matter abundance tocavg 5 95 mainly type i kerogen lamalginite which is in the immature to low mature stage organic carbon isotope data 13corg element ratios sr cu and c value and weathering indexes including cia ciw and pia together revealed that the region experienced a semihumid to semiarid palaeoclimate in the middle of the early cretaceous the increase in rainfall in unit ii enhanced the abundance of lake algae and surrounding terrestrial vascular vegetation and elevated the lake level which contributed to adequate sources and favourable preservation conditions for organic matter accumulation several lines of evidence including high sulfur contents the combination of vein pyrite and micritic dolomite positive eu anomalies and element geochemical correlations confirm the existence of intermittent low temperature white smoker type hydrothermal activity the decrease of oxygen content in lake bottom water may be related to the input of hydrothermal fluid which provided necessary nutrient elements for biological productivity according to palaeontological and radioisotope dating data it can be inferred that the black shales of the bayingebi formation are the product of the combined effect of global palaeotemperature rise in the early aptian stage of the early cretaceous and intermittent low temperature hydrothermal activity

peculiarities of salt lake sediments as potential source rocks in china abstract hypersaline lake sediments are widely distributed in china and can be good sources for petroleum the palaeogene sediments of the jianghan basin in eastern china are a typical example composed of salt lake evaporite clastic facies in fault subsided basins their organic matter is variable but is dominated by type ii kerogen the biological marker characteristics of core extracts and oils from the jianghan basin include i low oep values for n alkanes and occasionally an even odd predominance ii a high concentration of phytane iii a relatively high gammacerane 17 h 21 h hopane ratio and iv abundant mainly nickel porphyrins sample guang 33 k 33 is typical of the immature oils found in the jianghan basin geological and geochemical data both indicate that it was generated from source rocks in the maturity range r 0 0 45 0 55 its characteristics are similar to those of immature source rocks with high concentrations of phytane steranes triterpanes and nickel porphyrins and for an oil extremely low values for molecular parameters of maturity such as c 29 20s 20s 20r 14 h 17 h steranes c 32 22s 22s 22r 17 h 21 h hopanes and dpep dpep etio porphyrins

vertical and lateral distribution of lacustrine carbonate lithofacies at the parasequence scale in the miocene hot spring limestone idaho an analog addressing reservoir presence and quality lacustrine carbonate lithofacies in the hot spring limestone vary systematically at meter to decameter scales and record paleobathymetry limnologic conditions and paleogeographic influences this unit accumulated during the late miocene in a lake system in an extensional basin complex closely associated with lava flows and volcaniclastics sedimentology and sequence stratigraphy enable understanding and prediction of the occurrence distribution and character of lacustrine carbonates occurrence of lacustrine carbonates is a function of lake basin type in this case a volcanically mediated balanced filled lake basin that contains various lithofacies microbialite grainstone packstone wackestone and carbonate mudstone distribution of lithofacies is strongly controlled by depositional subenvironment and gradient through water depth bottom energy circulation and accommodation internal character of microbialites i e type size porosity vertical and horizontal permeability associated lithotypes diagenesis is influenced by stratal position at the parasequence scale and location along the depositional profile depositional reservoir quality characteristics such as microbialite porosity and thickness grainstone size and sorting and overall carbonate continuity and connectivity peak in the medial sublittoral zone conversely secondary diagenetic effects such as dissolution carbonate and quartz cement and possible authigenic clays are highest in the updip lake plain littoral zones and are less common lakeward thus the medial sublittoral zone has the optimum potential where primary depositional characteristics are best developed and negative secondary diagenetic effects are minimal these strata share many attributes with the cretaceous presalt systems of the south atlantic and can provide insights about controls on potential reservoir character distribution and connectivity for exploration and development

organic geochemistry of freshwater and alkaline lacustrine sediments in the green river formation of the washakie basin wyoming u s a abstract two members of the green river formation in the washakie basin have been analysed by organic geochemical and organic petrographic techniques and the results placed in a sequence stratigraphic framework one of these members the laney shale was deposited in a hydrologically closed alkaline lake under an arid climate and was characterized by high concentrations of alginite rich organic matter whereas the other the luman tongue was deposited in a hydrologically open freshwater lake under a humid climate and consisted of organic poor profundal lake mudstones and coaly lake margin sediments potential source rocks in both lake types have the potential for generating high wax oil at high subsurface temperatures 150 175 c at a heating rate of 5 k ma but the alkaline system is clearly more prolific the most abundant biological marker hydrocarbons were the 4 methylsteranes in both lake types though dinosteranes were found only in the laney shale oleanane was absent from the luman tongue despite an abundance of angiosperm palynomorphs intraformational heterogeneities were best documented for the laney shale where molecular differences in kerogen type occur at the parasequence level with early transgression maximum transgression and rejuvenation stages of lake history having its own kerogen type and distinctive high wax oil fingerprint thermal lability was shown to be linked to kerogen structure in particular the presence of alicyclic and oxygen containing moieties and these in turn are correlated with total organic carbon content and thence productivity degree of preservation some kerogen components appear to have originated via selective preservation whereas others may have been formed by diagenetic condensation reactions

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

productivity control on oil shale formation mae sot basin thailand abstract neogene oil shales from the freshwater lacustrine intermontane mae sot basin western thailand are examined in order to define a oil source rock potential b variations in molecular and isotopic geochemical characteristics and c the influence on source potential of organic matter productivity and preservation twelve samples spanning 7 m of section were examined using conventional isotopic molecular and organic petrographic methods of geochemical analysis temporal resolution is 2700 yr per sample because thermal maturity differences and fluid migration within the sample set are absent and organic matter type input variation is either minor or absent based on visual kerogen analysis we propose that organic matter differences among the samples are caused by variability in surface water productivity all samples are excellent potential source rocks vr 0 4 0 5 ro containing types i and ii organic matter modified van krevelen plot determination consisting of almost 100 fluorescent amorphous kerogen visual kerogen determination numerous diagnostic molecular markers and characteristics are present including perhydro carotene dammaranes norsterane s and novel distributions of tricyclic terpanes stable carbon isotope ratios of kerogens and extract fractions range over 5 and co vary with hydrogen index this covariance is attributed to temporal increases in surface water productivity leading to co2 limiting conditions and consequent increase in 13c of the organic matter in the photic zone during times of elevated productivity increased amounts of 13c enriched organic matter reached the water sediment interface thus times of greater productivity are accompanied by higher 13c and hydrogen index values with 13c related to productivity under co2 limiting conditions and hi related to the relative amount of the water column that was anoxic during deposition our findings suggest that in petroleum geochemical studies involving lacustrine source rocks 13c values must be used with caution as oil oil and oil source rock correlation parameters

carbon isotopic composition of individual biomarkers in gilsonites utah abstract carbon isotopic compositions of saturated hydrocarbon aromatic hydrocarbon nso resin and asphaltene fractions of vein forming gilsonites cowboy bonanza independence wagonhound and harrison veins in the ne uinta basin utah are all similar and isotopically resemble mahogany zone shale extracts of the green river formation 13 c 29 to 31 individual molecular fossils in the gilsonites show a wider variability in compositions indicative of their paleoecological origins within the eocene uinta greater green river paleolake system carbon isotopic compositions of c28 and c29 steranes 13 c 25 to 32 pristance and phytane 33 to 34 and perhydro carotene carotane 13 c 33 2 suggest that organisms producing these compounds grew near the lake surface the c33 carotenoid lexane is isotopically identical to the c40 carotenoid carotane supporting a common c40 carotenoid precursor two groups of hopanes can be differentiated in the gilsonites based on carbon isotopic compositions c29 c31 and c32 hopanes and moretanes 40 9 to 44 3 consistent with a source from midwater bacteria and c30 hopanes and moretanes 51 0 and 60 5 for which the strong 13c depletion suggests at least partial derivation from methylotrophs the isotopic signatures of these molecular fossils suggest the source beds of the gilsonites were deposited in a stratified paleolake system with a depositional environment similar to that which formed the mahogany zone shales of the piceance creek basin algal biomarkers in the gilsonites are isotopically uniform throughout the area of the gilsonite vein occurrence 1500 km3 and resemble those in the mahogany zone shale in the piceance creek basin over 50 km to the east this remarkable lateral uniformity suggests that very similar photic zone water conditions existed across the entire uinta piceance creek paleolake system at the time of deposition of the gilsonite source bed mahogany zone shale sterane isotopic compositions are effective for the genetic correlation of the solid bitumens immature oils in contrast the carbon isotopic compositions of the bacterial biomarkers in the gilsonites vary significantly suggesting that conditions in deeper waters of the paleolake system were more variable carbon isotopic signatures of individual hopane biomarkers in the green river formation appear to be valuable for identifying different source facies characteristics within the same paleolake depositional system

immature oil and condensate modification of hydrocarbon generation model for terrestrial organic matter petroleum has been found in canadian frontier basins in reservoirs which have undergone low levels of thermal alteration vitrinite reflectance 0 6 ro paraffin indices stable carbon and hydrogen isotope contents pristane to nc17 ratios and diterpenoid biologic markers have been used to assess the level of maturity of the hydrocarbons in the reservoir independently of the level of maturity of the reservoir itself and of the surrounding shale units in the tertiary of the beaufort mackenzie basin naphthenic oils and condensates have been generated from terrestrially derived organic matter in source rocks juxtaposed with the reservoir at reflectance levels of 0 4 to 0 6 ro however condensates discovered in reservoirs which are th rmally immature on the labrador shelf have undergone extensive vertical migration and can be classed as conventional mature to overmature condensates hydrocarbons discovered in the lower cretaceous of the beaufort mackenzie basin and also those of the scotian shelf are more or less in place in that they are at a level of thermal alteration about equivalent to that of the reservoirs in which they are trapped the source for the early oils and condensates is considered to be resinite occurring dispersed in coal fragments the proportion of resinite liptinite and vitrinite in the organic matter of terrestrial source rocks strongly controls both the level of thermal alteration necessary for the section to function as an effective source rock and the ultimate product gas oil or condensate which will be generated

organic geochemical characterisation of depositional palaeoenvironments of source rocks and oils in brazilian marginal basins abstract an investigation of bulk isotopic and molecular features of a wide selection of source rocks and oils from brazilian marginal basins ranging from lower cretaceous to tertiary in age provides a number of organic geochemical criteria that characterise and distinguish their depositional palaeo environments the methods employed include evaluation of organic carbon contents rock eval pyrolysis vitrinite reflectance measurements determination of carbon isotope ratios elemental and visual kerogen analysis assessment of oils and solvent extracts by liquid and gas chromatography and quantitative biological marker investigations using gc ms for aliphatic hydrocarbons and uv vis spectrophotometry for metalloporphyrins selected data were evaluated using principal component analysis the results enable the recognition and differentiation of seven depositional regimes lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate marine deltaic marine highly anoxic with a predominance of calcareous mudstone lithology and marine anoxic with predominance of siliciclastic lithology diagnostic features in the biological markers from these depositional environments include the carbon number distributions of n alkanes pristane phytane ratios absolute concentrations of carotane higher acyclic isoprenoids c 30 hopane and steranes and the abundance of the latter relative to 4 methylsteranes the occurrence and abundance of particular biological markers such as gammacerane tricyclic and tetracyclic terpanes 18 h oleanane 28 30 bisnorhopane and 25 28 30 trisnorhopane and the relative abundances of nickel and vanadyl porphyrins

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

origin of lacustrine rocks of wilkins peak member wyoming wilkins peak member of the green river formation with its interbeds of trona oil shale and dolomitic mudstone contrasts markedly with the predominantly oil shale and calcitic mudstone sequences of the remainder of the succession much discussion has centered on the origin of these lacustrine rocks a perennial meromictic stratified lake model has been replaced in recent years by a playa lake model the subsurface stratigraphy however was not well known when the models were developed paleogeographic reconstruction indicates that the region was subjected to variations in hydrographic conditions mainly in response to climatic fluctuations during humid subtropical periods widespread during the deposition of the tipton shale member and laney member the lakes were p edominantly open meromictic systems with rivers entering the basin from the north these environmental conditions were modified during deposition of the wilkins peak member as the climate became more arid and along the southern margin of the basin shallow saline alkaline playa lakes formed in response to these changes the widespread occurrence in the subsurface of fluvial clastic sequences of the wasatch formation associated with the wilkins peak member would indicate that the playa lakes were frequently flooded and freshened by southern drainage systems therefore the lakes were continuously undergoing modifications under the influence of climatic and possibly tectonic processes a composite model is supported that combines aspects of both the meromictic and playa lake models beca se of these complexities it is unlikely that one modern lake can serve as an analog for ancient lake gosiute

changing lake dynamics and sequence stratigraphy of synrift lacustrine strata in a half graben an example from the triassic ischigualasto villa union basin argentina well exposed triassic rift strata from the ischigualasto villa union basin nw argentina include a 80 to ca 515 m thick lacustrine dominated package that can be correlated across a half graben using key stratigraphic surfaces sequence boundaries lacustrine flooding surfaces and forced regressive surfaces the characteristics of the synrift lacustrine fill in different parts of the half graben have been examined and the mechanisms controlling sedimentation inferred a variety of sedimentary environments are recognized including volcaniclastic floodplain mildly saline lake and playa lake offshore lacustrine delta front to fluvial dominated and wave dominated deltas distributary and fluvial channel and interdistributary bay the succession can be divided into four stratigraphic sequences ss1 to ss4 the oldest of which ss1 contains volcaniclastic fluvial and saline lake deposits it is thickest close to the western border fault zone reflecting more rapid subsidence here accommodation exceeded sediment and water input during ss1 the second and third sequences ss2 and ss3 mark the onset of widespread lacustrine sedimentation reflecting a balance between accommodation creation and water and sediment fluxes sequences ss2 and ss3 are represented by offshore meromictic lacustrine and deltaic deposits the latter mostly sourced from the flexural and southern axial margins of the half graben the presence of stacked parasequences bound by lacustrine flooding surfaces is related to climatically induced lake level fluctuations superimposed on variable rates of subsidence on the controlling rift border fault zone the youngest sequence ss4 is represented by the deposits of littoral lacustrine and shallow shelf deltas distinguished by a change in lithofacies palaeocurrents and sandstone composition suggesting a switch in sediment supply to the footwall margin to the nw the change in the sediment source is related to reduced footwall uplift the possible presence of a relay ramp and or supply from a captured antecedent drainage network during ss4 the rate of creation of accommodation was exceeded by the sediment and water discharge the stratigraphic evolution of lacustrine strata in the half graben was mainly controlled by tectonic processes including subsidence rate and the growth and evolution of the border fault zone but changing climate inducing changes in water balance and lake level and autocyclic processes delta lobe switching were also important

petroleum geochemistry and depositional setting of lacustrine source rocks abstract lacustrine sequences are increasingly being recognised as hosts for commercial reserves of petroleum petroleum source rocks in lacustrine sequences have organic carbon contents ranging from 20 and kerogen types range from type i to type iii the organic matter can be of land plant algal or bacterial origin most undegraded lacustrine oils are extremely paraffinic and waxy but a few are asphaltic and rich in sulphur the crude oils and source rocks contain a wide diversity of biological marker compounds reflecting different source inputs the diversity of chemistries displayed by lacustrine source rocks and crude oils reflect the wide variety of organic source materials and depositional conditions operative in lakes lacustrine sequences preserved in the geological record represent sediments deposited in fluvial lakes on humid flood plains and tectonic lakes in humid semi arid and arid environments preservation of organic matter in lakes is dependent on the formation of anoxic or micro oxic bottom waters this is favoured by stratification of lake waters brought about by temperature and salinity contrasts organic material preserved in oligotrophic lakes is largely of land plant origin which has been extensively modified by bacteria under mildly oxidizing conditions and supplemented by the bacterial remains source rocks of this type are found in 1 fluvial lacustrine settings e g jurassic of eromanga basin australia and 2 the oligotrophic phase of larger tectonic lakes e g early stages of green river formation uinta basin usa as these freshwater lakes become productive algal remains are contributed to the sediment and anoxic bottom waters can become more firmly established the green algae pediastrum and botryococcus appear to be particularly important although land plant detritus is still significant e g cretaceous source rocks songliao basin china saline lakes conditions tend to restrict the diversity of the source biota although preservation may be enhanced through anoxia brought about by salinity stratification and inhibition of bacterial decay e g later stages green river formation uinta basin usa sulphate rich and hypersaline lacustrine systems result in the formation of sulphur rich sources and oils e g jianghan basin china because of the diversity of organic matter types maturation criteria for hydrocarbon generation in lacustrine sequences also vary however in most cases higher maturation levels are required for significant hydrocarbon generation at present it is uncertain the extent to which algal and bacterial organic matter contribute to the source for the waxy hydrocarbons which are characteristic of lacustrine oils organic rich rocks formed in large freshwater and saline lakes are the most productive type of lacustrine source rock although sources formed in lakes of flood plains and deltas are also widespread

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

junggar basin northwest china trapped late paleozoic ocean abstract the junggar basin originated during the late paleozoic as either a remnant lower to mid paleozoic ocean basin or a mid carboniferous back arc intra or inter arc basin bounded by emergent volcanic arcs south of the siberian craton the retreating junggar sea left behind a regressive sedimentary section comprising at least 3 4 km of marine volcaniclastics in the southern junggar area sandstones deposited in the junggar basin since the devonian are exclusively volcaniclastic demonstrating that precambrian basement rocks have never been exposed in the basin and supporting the hypothesis that the junggar is underlain by oceanic crustal materials the mid carboniferous junggar ocean may have been a remnant ocean basin of early to mid paleozoic age or alternatively may have been an extending intra or inter arc basin formed behind an emergent volcanic arc in the northern turpan region subsequent strike slip deformation and the general sparsity of geologic and geophysical data from the junggar area make it difficult to distinguish between these models late early permian through triassic sediments of the junggar basin are exclusively non marine deposited in a flexurally subsiding foreland basin during initial uplift of the ancestral tian shan mountains the sedimentary section deposited during the late permian early triassic appears to be inconsistent with a proposed rifting episode during this period

genetic sequence stratigraphic framework depositional style and hydrocarbon occurrence of the upper cretaceous qyn formations in the songliao lacustrine basin northeastern china the qingshankou yaojia and nenjiang qyn formations in the songliao basin of northeastern china can be used to illustrate the application of sequence stratigraphic analysis in a lacustrine setting and to provide a good example of hydrocarbon occurrence in a lacustrine stratigraphic framework the qyn genetic stratigraphic sequence bounded by maximum flooding surfaces or beds is a low frequency second order sequence or supercycle in a lacustrine basin with a ramp margin use of subaerial unconformity and transgressive surfaces allows further subdivision of the qyn sequence into a progradational systems tract lowstand prograding complex and retrogradational systems tract delta system styles are dominated by the physiography and relative intensity of fluvial and wave rocesses q1 and n1 maximum flooding related deposits used to identify the qyn genetic stratigraphic sequence boundaries are the main petroleum source rocks and regional seals and play an important role in determining hydrocarbon distribution in the songliao basin the y1 lowstand prograding complex and y2 3 retrogradational systems tract in the northern part of the basin are the most important reservoir and producing intervals within the qyn sequence

organic geochemical characteristics and organic matter enrichment of mudstones in an eocene saline lake qianjiang depression hubei province china abstract the qianjiang depression is a typical eocene hypersaline lake basin developing good source rocks in the qianjiang formation which have recently been identified as a potential target for saline lacustrine shale oil exploration previous studies have only focused on estimates of source rock potential and reservoir quality however studies on organic matter enrichment mechanisms in evaporative environments are limited based on organic geochemical and mineralogical data as well as sedimentological analyses we researched the factors controlling differences in organic matter enrichment in the basin the results show that total organic carbon toc contents are closely associated with lithofacies with distinct variations three main lithofacies associations las were identified 1 glauberite rich la1 with medium toc 2 carbonate rich la2 with high toc and 3 anhydrite rich la3 with low toc the distribution of biomarkers from 14 samples indicate both higher land plants and aquatic organisms were involved in the organic matter accumulations combining experimental results on gammacerane c30 hopane extended tricyclic terpane ratio etr sr ba v ni and sedimentary characteristics we analyzed the sedimentary environments of the three las la1 was deposited in a salinity stratified waterbody with strong evaporation la2 was deposited in a still stratified deep waterbody whereas la3 was deposited in a disturbed saline waterbody sedimentary environments not only controlled the formation of the lithofacies but also influenced the organic matter sources and preservation relatively low salinity strong anoxic condition without physical disturbance appropriate nutritional terrigenous material inputs and algal blooms produced the best organic matter enrichment in the saline lake system

a model of hydrocarbon generation from type i kerogen application to uinta basin utah we have developed a computer model that can predict when and how much oil and gas are generated from a source rock during its burial and later uplift kinetic parameters for the oil and gas generation reactions are obtained from high pressure pyrolysis experiments carried out over a wide range of heating rates and temperatures in our kinetic model which applies only to green river shale we use a single activation energy of 52 4 kcal mole and different pre exponential factors for different products of primary pyrolysis which allows us to extrapolate laboratory derived kinetics to geologic heating rates this model is in contrast to the wide distributions of activation energies or artificially low apparent activation energies used in some models of petroleum formation hen extrapolated to geologic heating rates on the order of 10 c m y our kinetics show that the temperature of the maximum rate of oil generation tp changes by about 15 c when the heating rate is changed by an order of magnitude changes in pressure have relatively minor effects on the kinetics of oil generation but are important for gas generation reactions we used geophysical data from oil fields in the uinta basin of utah to develop a thermal history model of green river formation source rocks this time temperature history was used to predict the maturation level of the kerogen at a given depth and to predict changes in the compositional characteristics of the oil the shape of calculated oil generation rate curves as a function of depth in the basin mimics the shape of the overpressure curves this similarity suggests that oil gas generation may be an important cause of overpressuring maturation levels and compositional characteristics of the oil predicted by our model agree very well with characteristics of the oil recovered from the basin

geochemistry of oils from the junggar basin northwest china the junggar basin of northwestern china is a structural basin containing a thick sequence of paleozoic pleistocene rocks with estimated oil reserves of as much as 5 billion bbl analyses of 19 oil samples from nine producing fields and two oil stained cores in the junggar basin revealed the presence of at least five genetic oil types the geochemistry of the oils indicates source organic matter deposited in fresh to brackish lake and marine environments including coaly organic matter sources the volumetrically most important oil type discovered to date is produced from late carboniferous middle triassic reservoirs in the giant karamay field and nearby fields located along the northwestern margin of the junggar basin oil produced from the mahu field located downdip in a depression east of the karamay field is from a different source than karamay oils unique oil types are also produced from an upper permian reservoir at jimusar field in the southeastern part of the basin and from tertiary oligocene rocks at dushanzi field and lower jurassic rocks at qigu field both located along the southern margin of the basin previous studies have demonstrated the presence of upper permian source rocks and the possibility of mesozoic or tertiary sources has been proposed but not tested by geochemical analysis although analyses of some possible jurassic coal source rocks have been reported our findings indicate that several effective source rocks are present in the basin including local sources of mesozoic or younger age for oil accumulations along the southern and southeastern margins of the basin future exploration or assessment of petroleum potential of the basin can be improved by considering the geological relationships among oil types possible oil source rocks and reservoirs

structural features and genesis of microscopic pores in lacustrine shale in an oil window a case study of the dongying depression the paleogene shale of the dongying depression a continental basin in eastern china is taken as the study subject to examine the microscopic features of lacustrine shale reservoirs in the oil window this study shows that shale pores in this evolutionary stage are present at the micrometer to nanometer scale but fractures commonly have extension distances at the millimeter scale pores and fractures can be divided into three types namely primary pores secondary pores and cracks primary pores commonly have good connectivity at shallow burial depth with the increase of burial depth primary porosity is reduced because of compaction and cementation secondary pores are important in shale including dissolved pores inside grains and at grain edge and dissolution pores inside the hybrid of organic matter om and clay minerals and evaporite minerals including carbonates or sulfates types of cracks were observed bedding fissures dissolution fractures and structural fractures the development of bedding fissures is related to the deposition of shale laminae the formation of dissolution fractures is related to acidic fluids such as organic acids and hydrogen sulfide whereas the formation of structural fractures is jointly controlled by fault development fluid overpressure and lithofacies the pores and fractures in the oil window of lacustrine shale can store and channel oil and gas the hybrid om clay carbonate sulfate and the pores inside are important through the oil window moreover the development of the pores depends not only on hydrocarbon generation but also on the interaction of hydrocarbons and organic acid dissolution this finding has important significance in the accumulation of oil and gas in continental shales

a biomarker study of immature crude oils from the shengli oilfield people s republic of china abstract a suite of crude oils from the shengli oilfield in northwestern china was subjected to detailed chemical analysis crude oils in this suite believed to be derived from source rocks deposited under fresh brackish and saline environments have chemical compositions and biological marker compounds indicative of immature source rocks in this respect the crude oils are unusual apparently having been formed and expelled from source rocks that have been subjected only to mild thermal stress prior to the main zone of petroleum generation

petroleum geology of cretaceous tertiary rift basins in niger chad and central african republic this overview of the petroleum geology of rift basins in niger chad and central african republic car is based on exploration work by exxon and partners in the years 1969 1991 the work included 50 000 km of modern reflection seismic 53 exploration wells 1 000 000 km2 of aeromagnetic coverage and about 10 500 km of gravity profiles the results outline ten cretaceous and tertiary rift basins which constitute a major part of the west and central african rift system wcars the rift basins derive from a multiphased geologic history dating from the pan african approximately 750 550 ma to the holocene main rifting was probably caused by the stretching and subsidence of african crustal blocks during the breakup of gondwana in the early cretaceous and by r activated plate movements in the early tertiary wcars in the study area is divided into the west african rift subsystem was and the central african rift subsystem cas was basins in niger and chad are chiefly extensional and are filled by up to 13 000 m of lower cretaceous to holocene continental and marine clastics the basins contain five oil 19 43 api and two oil and gas accumulations in upper cretaceous and eocene sandstone reservoirs the hydrocarbons are sourced and sealed by upper cretaceous and eocene marine and lacustrine shales the most common structural styles and hydrocarbon traps usually are associated with normal fault blocks cas rift basins in chad and car are extensional and transtensional and are filled by up to 7500 m of chiefly lower cretaceous continental clastics the basins contain eight oil 15 39 api and one oil and gas discovery in lower and upper cretaceous sandstone reservoirs the hydrocarbons are sourced by lower cretaceous shales and sealed by interbedded lacustrine and flood plain shales structural styles range from simple fault blocks through complex flower structures the main hydrocarbon traps are in contractional anticlines geological conditions favor the discovery of potentially commercial volumes of oil in wcars basins of niger chad and car

re sedimented deposits in the rift section of the campos basin abstract an integrated petrologic sedimentologic stratigraphic seismic study of the lagoa feia group rift section of the campos basin has shown that rift sedimentation was dominantly intrabasinal carbonate and stevensitic deposits with siliciclastic deposits restricted to the proximity of graben border faults the bivalve bioclastic rudstones coquinas that constitute the rift reservoirs show commonly limited abrasion of the bioclasts and were deposited both on basement highs and lows throughout the rift section although in situ deposits of stevensite ooids and peloids occur dominantly at the base of the succession these particles are ubiquitous to the entire rift section mixed in variable proportion with siliciclastic and carbonate sediments the environmental conditions required for the formation of stevensite and the growth of bivalves are mutually exclusive as stevensite forms only at ph greater than 10 while bivalves cannot tolerate ph greater than 9 the common mixture of well rounded basaltic rock fragments with angular granitic gneissic rock fragments and feldspars in the sandstones and conglomerates indicates recycling of epiclastic deposits from the early rift section combined with first cycle contribution from the plutonic basement the studied cores show no evidence of subaerial exposure and there is a lack of bioturbation suggesting harsh environmental conditions the rift deposits are dominantly massive or faintly laminated with diffuse facies boundaries structures indicative of unidirectional or oscillatory flow are subordinate integration of seismic sedimentologic and petrographic evidence indicates that the campos basin rift section is formed mostly by re sedimented gravitational deposits the onset of the rift sedimentation occurred in synformal depressions where bivalve banks or stevensite ooids were formed in shallow lacustrine environments under variable alkalinity conditions with the development of half grabens and concentration of the tectonic activity along the border faults recurrent tectonic events promoted the mixing and gravitational re deposition of stevensitic clastic and bioclastic sediments in deeper fault bounded troughs large scale units hundreds of meters thick were generated by major tectonic events whereas compositional variations in the scale of meters were possibly a product of lake level climatic fluctuations thus due to syn rift and mainly to post rift erosion the neo aptian unconformity the preserved rift section of the lagoa feia group comprises mostly sediments deposited in the central troughs of the half graben structures marginal sediments were extensively eroded and re sedimented as gravity driven mixed deposits this new model constructed form the integration of seismic stratigraphic sedimentologic and petrologic data diverges substantially from the presently accepted model for the sedimentation of the rift section opening new possibilities for the exploration of campos basin as well as of similar settings as in the adjacent santos basin

diverse sedimentary conditions during deposition of coal and oil shale from the meihe basin eocene ne china the meihe basin in northeastern china is a normal fault controlled basin filled with eocene nonmarine deposits the sediments assigned to the meihe formation sediment grain sizes core study well log analysis and micropetrographic study combined with sedimentary facies analysis indicate that the main sedimentary facies of the meihe basin represent fan delta lake and turbidite deposits thick coal seams that are mainly distributed in the eastern part of the studied area were deposited in the swamp facies of the lower coal bearing member oil shale was mainly deposited in the deep lake represented by the mudstone member and is mainly distributed in the southern part of the studied area in the lower coal bearing member organic rich sediments are characterized by toc content between 0 6 wt and 43 1 wt and contain type ii and iii kerogen the thick coal seams are the result of high landplant productivity and good preservation conditions thin coal seams in the fan delta plain resulted from the migration and erosion of the fan delta channel in the shallow lake and fan delta front limited productivity coupled with dilution by inorganic matter resulted in lower organic matter content in themudstonemember oil shale and mudstone rich in organic matter were deposited in a deep lake with an average toc content of 3 4 wt the origin of the organic matter was mainly algae and aquatic plants mixed with land plants the improved preservation conditions and high bioproductivity in this environment resulted in three oil shale layers in the lower part of this sedimentary succession three coal bearing and oil shale bearing fault basins lie adjacent to the dunhua mishan fault zone among which the fushun basin is located in the southwest the meihe basin is in themiddle and thehuadian basin is in the southeast from the fushun basin to the huadian basin the oil shale and coal seams have distinct sedimentation characters laterally vertically in each basin the organic matter sources all have the same variation trend from land plants to land plants mixed with algae to algae then to algae mixed with land plants and the toc content also shows a similar trend from high to medium high then to low in each basin

kerogen asphaltene sulfur relationships in sulfur rich monterey oils abstract monterey oils in the santa maria basin onshore and offshore are generally low maturity oils because of low thermal exposure relatively shallow burial for short times they are generated as heavy high sulfur oils because of the composition of the unusual type ii source kerogens which are exceptionally rich in organic sulfur 8 14 these high sulfur kerogens which we designate type ii s appear to generate oil at significantly lower thermal exposures than ordinary type ii kerogens with less than 6 s in contrast to common type ii kerogens which generate oil largely by cleavage at oxygen bridge groups and carbon carbon bonds eliminating co2 h2o and hydrocarbon fragments type ii s kerogens have an additional complement of weak bonds associated with bound sulfur the preferential cleavage at weak sulfur linkages tends to produce larger fragments leading to high initial amounts of asphaltenes resins and sulfur rich aromatics together with smaller amounts of saturated hydrocarbons elemental analyses of monterey kerogens and asphaltenes clearly support the concept that the asphaltenes are essentially fragments of kerogen cleaved sufficiently to be soluble or peptized in this heavy oil system solubilization of asphaltenes is attributed to their interactions with the abundant resins and aromatics this sysstem is sufficiently stable under source and reservoir conditions to allow expulsion and migration for reasonable distance without significant fractionation or changes in gross properties initial asphaltenes have essentially the same atomic h c ratios as the source kerogen but have significantlyy lower o c ratios and slightly lower s c ratios the n c ratios are nearly the same for kerogens and their derived asphaltenes with increasing maturity the h c ratios in asphaltenes decrease much like maturation changes in kerogen the s c ratio also decreases significantly however the o c ratios initially low in asphaltenes and n c ratios increase slightly due to material balance caused by other losses these element composition and atomic ratio relationships allow some important inferences concerning source kerogen composition from analysis of asphaltenes alone this can be useful when potential source rock samples are not available for analysis and or when a choice between alternate source rock possibilities must be made

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

characteristics and origin of lacustrine source rocks in the lower cretaceous erlian basin northern china abstract four lacustrine rift sub basins in the erlian basin one of the most petroliferous basins in northern china have been analyzed to characterize source rock potential to reveal environmental and ecological changes and to construct depositional models for lacustrine source rocks in different tectonic settings the first member of the tengger formation in these sub basins is characterized by a wide range of total organic carbon contents hydrogen indices and kerogen types these sub basins have dissimilar boundary fault activities and sedimentation rates the differences in border fault activity and sedimentation rate are consistent with changes in productivity redox conditions and clastic influx input the carbon isotopic composition of carbonates in mudstone samples suggests that the productivity of aer and wuli sub basins is higher than that of naoer and saihan sub basins differences in tectonic conditions also result in different redox conditions of depositional environments total reduced sulfur and pr ph ratios show an oxidizing environment in aer and wuli sub basins while a reducing environment was present in naoer and saihan sub basins with more active boundary faults and higher sedimentation rates the terrigenous organic matter inputs to aer and wuli sub basins are higher than naoer and saihan sub basins this can be confirmed by relative steranes abundances different tectonic conditions existed in different sub basins which lead to variations in ecological communities in the lake systems these environmental and ecological changes enable us to construct models for the deposition of lacustrine source rocks under different tectonic backgrounds during source rock deposition in aer and wuli sub basins the high influx of clastic sediments carrying high terrigenous organic matter and dissolved inorganic carbon and nitrate into the lake might have sustained high productivity and oxidizing conditions due to high influx of clastic sediments and unstable water column stratification the depositional environment of aer and wuli sub basins are oxidizing in a high productivity lake there is still significant organic matter accumulation in oxidized environment after oxidative degradation the high productivity is the dominant factor controlling the formation of organic rich sediments and the deposition of source rocks in aer and wuli sub basins in naoer and saihan sub basins the depositional environment during source rock formation is reducing due to low influx of clastic sediments with low productivity in low productivity lakes such as naoer and saihan sub basins which are low productivity lakes redox condition substitutes for productivity and becomes the predominant factor controlling the formation of lacustrine source rocks it is evident that the synergetic evolution of depositional environments and organisms in a lake system accounts for the formation of source rocks with different characteristics the proposed models may have important implications for source rock prediction in other lacustrine rift basins

organic matter composition and distribution through the aptian albian lacustrine sequences of the araripe basin northeastern brazil abstract the main characteristics and distribution of organic matter have been studied through several aptian albian lacustrine units rio da batateira crato and ipubi formations araripe basin ne brazil six main facies have been distinguished on the basis of their lithological sedimentological characteristics and the type and amount of organic matter 1 marginal lacustrine deltaic massive to coarsely laminated mudstones and sandstones found as lenticular sheet and channel infills 2 oxic marginal lacustrine massive to poorly laminated mudstones 3 oxic suboxic inner lacustrine mudstones and laminated bioclastic mudstones 4 anoxic inner lacustrine dark mudstones 5 anoxic inner lacustrine dark clay carbonate rhythmites and 6 anoxic inner lacustrine finely laminated dark micritic limestones these facies make up decimeter to several meter thick parasequences which stack up in several tens of meters thick successions water level changes and variations of the detritic sediment contribution in the basin controlled the evolution of the depositional system palynomorph associations showed that the lacustrine system evolved in an arid semiarid tropical area where the most characteristic flora consisted of conifers gnetales bennettitales and early angiosperms in facies 1 to 3 organic matter was scarce poorly preserved and mainly derived from higher land plants facies 4 is characterised by containing abundant algal bacterial derived well preserved organic matter facies 5 and 6 contained mainly branchlets and pollen debris blown by the wind or fed by lacustrine underflows the pattern of organic matter accumulation and preservation corresponds well with cyclical palaeoenvironmental changes from anoxic to oxic bottom conditions and from a fresh to saline upper water layer which affected the shallow lacustrine system the deposition of thin organic matter rich mudstones facies 4 probably occurred during higher water levels which resulted in relatively low salinity waters and low detrital contribution to the inner lacustrine zones less significant organic matter accumulation is recorded in the clay carbonate rhythmites and in the limestones facies 5 and 6 due to scarce autochthonous aquatic organic matter deposition and pervasive intense bacterial degradation caused by persistent meromictic conditions large differences in the degree and path of evolution of the humic material derived from higher land plants have been detected depending on the depositional conditions the humic material in the oxic facies underwent humification and gelification and had the highest huminite reflectances whereas it showed suppressed reflectance values in the oil shales facies 4 and in the carbonate dominated facies in the latter extensive bacterial reworking of humic material is also observed these differences are considered significant and applicable to other case studies in terms of evaluating the maturity of organic matter in ancient lacustrine systems

monitoring tectonically controlled marine to lacustrine transitions using organic facies ridge basin california u s a abstract ridge basin is an elongate intermontane basin filled with upper miocene pliocene clastics located 80 km north northwest of downtown los angeles over 13 km of marine lacustrine and fluvio deltaic sandstones and shales are present because of southeastward depocenter migration throughout basin development no more than 4 5 km of vertical section are present in any one location this has resulted in an ideal situation to study organic facies variability namely a thick thermally immature stratigraphic succession with only minor variations in maturity level in this paper we use molecular isotopic and petrographic data to help identify systematic variability in organic facies in the castaic ridge route and peace valley fms all late miocene and relate these variations to the paleolimnology tectonic history and oil source rock potential of the basin as strike slip movement continued along the san gabriel fault during the late miocene the sedimentation regime changed from a marine dominance to one controlled by lacustrine and fluvio deltaic processes this transition results in changes in the organic facies within the basin as reflected in a a systematic decrease in organic carbon isotope ratios b an increase in relative yields of phenolic and n aliphatic structures in the kerogen pyrolysate c an increasing occurrence of perhydro carotene indicating episodic development of a halocline in the water column and d decreasing pristane phytane and c 29 c 28 sterane ratios unusual patterns of kerogen maceral distribution and a ring sterane methylation are also observed these geochemical data support the existence of a marine embayment in the early late miocene yielding to a lacustrine and fluvio deltaic setting which experienced considerable variation in bathymetry salinity and oxicity low levels of thermal maturity preclude the occurrence of hydrocarbon source rocks although source rock potential is present in sporadic localities optical and molecular maturity indicators show no systematic variation with stratigraphic succession this lack of variation is consistent with the known tectonic development in the basin and the shingled sedimentation pattern resulting from a migrating depocenter internal variability in the sterane and hopane epimer ratios may eventually be useful in estimating the uneven extent of overburden in the peace valley and ridge route fms leading to applications elsewhere in intermontane lacustrine basins with tectonically migrating depocenters

lake type controls on petroleum source rock potential in nonmarine basins based on numerous empirical observations of lacustrine basin strata we propose a three fold classification of lacustrine facies associations that accounts for the most important features of lacustrine petroleum source rocks and provides a predictive framework for exploration in nonmarine basins where lacustrine facies are incompletely delineated 1 the fluvial lacustrine facies association is characterized by freshwater lacustrine mudstones interbedded with fluvial deltaic deposits commonly including coal shoreline progradation dominates basin fill resulting in the stacking of indistinctly expressed cycles up to 10 m thick in map view the deposits may be regionally widespread but laterally discontinuous and contain strong facies contrasts transported terrestrial organic matter contributes to mixed type i iii kerogens that generate waxy oil type i kerogen is hydrogen rich and oil prone type iii kerogen is hydrogen poor and mainly gas prone the luman tongue of the green river formation wyoming and the honyanchi formation junggar basin china provide examples of this facies association which is also present in the songliao basin of northeastern china the central sumatra basin and the cretaceous doba doseo basins in west central africa 2 the fluctuating profundal facies association represents a combination of progradational and aggradational basin fill and includes some of the world s richest source rocks deposits are regionally extensive in map view having relatively homogenous source facies containing oil prone type i kerogen examples include the laney member of the green river formation wyoming the lucaogou formation junggar basin china the bucomazi formation offshore west africa and the lagoa feia formation campos basin brazil 3 the evaporative facies association represents dominantly aggradational fill related to desiccation cycles in saline to hypersaline lakes and may include evaporite and eolianite deposits sublittoral organic rich mudstone facies are relatively thin but may be begin page 1034 quite rich and widespread the highest organic enrichment coincides with the deepest lake stages low input of land plant organic matter results in minimal lateral contrasts in organic content in some cases a distinctive type i s sulfur rich kerogen may generate oil at thermal maturities as low as 0 45 vitrinite reflectance equivalent examples include the wilkins peak member of the green river formation wyoming the jingjingzigou formation junggar basin china the jianghan and qaidam basins china and the blanca lila formation argentina

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

eolian sandstones in upper triassic lower jurassic red beds of the fundy basin nova scotia abstract eolian sandstones occur interbedded with alluvial fan and braided river red beds in the upper triassic wolfville formation and at the base of the lower jurassic mccoy brook formation in nova scotia extensive semiaridity and aridity in the subtropical rift valley favored deposition of eolian sandstones caliche paleosols alluvial fan conglomerates braided river alluvium and playa mudstones in postdrift configuration paleowinds blew to the southwest west and northwest down the valley reflecting the direction of trade winds at 25 n paleolatitude a three step hierarchy of surfaces truncates cross beds first order bedding planes of low relief extend for at least hundreds of meters truncating all eolian structures these surfaces were sculptured by desert flash floods and then deflated to ventifact bearing bimodal regs second order surfaces bound cross bed sets and are mostly concave up and dip downwind recording shifts in migration direction of individual dunes or dunes superimposed on larger dune structures third order surfaces within cross bed sets formed on the lee sides of dunes due to fluctuations in wind direction and strength barchans initially developed on the alluvial fan and braided river alluvium later coalescing into barchanoid transverse ridges as evidenced by the internal geometry of the eolian sandstones p

characteristics of selected petroleum source rocks xianjiang uygur autonomous region northwest china 1 the sedimentary basins of xinjiang uygur autonomous region china are moderately to poorly explored for petroleum volumetric adequacy of petroleum source rocks is a critical exploration risk in these basins particularly because source rock data are limited this study provides new source rock data and speculatively assesses the source rock potential of xinjiang basins the junggar zhungaer basin the best explored of the xinjiang basins and containing a giant oil field is underlain in many areas by an upper permian lacustrine oil shale sequence remarkable for its organic richness and oil source quality depending on its position in the basin the permian section ranges from immature to overmature and is inferred to be the principal source of oil in the basin upper triassic middle jurassic coal measures including lacustrine rocks constitute a secondary source rock sequence in the basin the smaller intermontane turpan tulufan basin contains a very similar upper triassic middle jurassic sequence which where sufficiently buried probably comprises the only significant oil source sequence in the basin the vast tarim talimu basin offers the greatest variety of potential source rocks of all xinjiang basins but remains the least well documented from limited but geologically planned and focused sampling cambrian carboniferous and permian strata are not considered major oil contributors in the dominantly shallow marine paleozoic section of the northern tarim basin only ordovician black shales appear to have significant potential the upper triassic middle jurassic sequence of the northern tarim basin is similar to that of the junggar and turpan basins a section rich in coal and lacustrine shale that constitutes another potentially significant oil source due to the size stratigraphic packaging and structural relief of the northern tarim basin paleozoic and mesozoic potential il source beds range from immature to overmature

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

outcrop architecture of a fluvio lacustrine succession upper triassic yanchang formation ordos basin china abstract although several studies have considered the sedimentary facies of the upper triassic yanchang formation in terms of their hydrocarbon potential in the petroliferous ordos basin such studies have mostly interpreted subsurface data and few have systematically examined the detailed outcrop based anatomy of this succession this study characterizes a series of well exposed outcrop sections along an 80 km long e w oriented series of road cuttings in the southeast ordos basin to reconstruct the sedimentary architecture of a fluvio lacustrine succession and determine the principal controls that governed the style of accumulation and preservation the yanchang formation is divided into 10 depositional units chang 10 base to chang 1 top that record the sedimentary evolution of a series of large scale fluvial systems that constructed delta front and pro delta bodies as they entered a large interior draining lake detailed analysis of the internal architectures of the delta front bodies records the mechanism of growth of a large scale shallow water delta succession lacustrine subaqueous distributary channels are composed of 3 15 m thick sandstone fills such channelized bodies are highly elongate and many can be traced several kilometres such bodies can be shown to be commonly associated with thin bedded mouth bar and subaqueous interdistributary bay deposition the progradational architecture of the delta front elements is difficult to recognize on outcrop scale deposits of the chang 10 to 1 units record 4 major lacustrine transgressive regressive cycles during the late triassic transgressive events are signified by the widespread occurrence of 10 20 m thick oil shale prone intervals regressive events are signified by the progradational stacking towards the basin centre of sandstone prone facies associations mainly accumulated in fluvial channel delta plain and upper delta front environments the uppermost chang 1 interval records late stage filling of the lacustrine basin the transgressive regressive cycles equate to sequences that can be correlated across the region development of which was controlled by a combination of changes in the rate of tectonic subsidence the rate of sediment delivery from the basin margin hinterland and climate factors that were themselves influenced by intracontinental growth of the neighbouring qinling orogen

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

depositional subenvironments in an arid closed basin the wilkins peak member of the green river formation eocene wyoming u s a the wilkins peak member of the green river formation is a non marine dolomitic deposit that formed in an arid hydrologically closed basin a transect from the margin to the centre of the wilkins peak basin was examined in outcrop exposures in the south eastern corner of the basin and was supplemented with published core descriptions the rocks were divided into seven facies based upon lithology layering style and sedimentary fabrics 1 af facies quartzose conglomerates and sandstones representing sandy alluvial fans coming from the uinta mountains 2 sf facies quartzose peloidal dolomitic sandstones which represent sheet flood deposits extending basinward from the alluvial fans 3 dm facies irregularly laminated dolomitic mudstones with abundant mudcracks which represent sheet flood deposits on a subaerially exposed mudflat 4 el facies dolomitic mudstones with regular lamination and fewer but larger mudcracks representing sporadically exposed lake margins or shallow ponds 5 pl facies finely laminated oil shales and dolomitic mudstones with rare mudcracks which represent shallow perennial lakes 6 sm facies trona or halite deposits with dolomitic mudstone partings or dolomitic mudstones and sandstones disrupted by evaporites of varied morphology these represent a central salt pan and the surrounding saline mudflat 7 as facies arkosic sandstones siltstones and mudstones which represent braided river and more basinal deltaic plain deposits the five dolomitic facies form poorly defined cycles representing the intersection of sheet floods with a lake which transgressed and regressed in response to climatic variations there are at least forty 3 4 m thick cycles in the wilkins peak and one large scale cycle comprising the whole member which mimics the facies changes of the smaller cycles this is compatible with the transitions of the wilkins peak member to the tipton and laney members as climatic responses and not shifts in drainage the sheet flood sandstones actively aggrading subaerial mudflats and bedded evaporites of the wilkins peak are apparently unique within the green river formation they reflect the unusual provenance and hydrology of the wilkins peak and suggest chemical and sedimentary models established for the other green river members will not be applicable

stratigraphic response to saline lake level fluctuations and the origin of cyclic nonmarine evaporite deposits the pleistocene blanca lila formation northwest argentina stratigraphic analysis of pleistocene nonmarine bedded evaporites in northwest argentina elucidates the effect that episodic saline lake expansion and contraction have on the stratigraphic completeness of units deposited and preserved in a continental saline environment stratigraphic successions in these rocks contain features that relate uniquely to fluctuations in saline lake level bounding the top of each succession is a surface with evidence for an abrupt increase in water depth because sediment accumulation and stratal preservation vary spatially as a function of lake level the degree of stratigraphic completeness varies among locations these results have implications for attempts to extract the record of continental climate change from saline lake strata bedded evaporites in these strata accumulated in a saline lake characterized by a marginal zone of gypsum and ulexite with clastic interbeds and an accumulation of halite in the saline lake center four internally conformable successions of genetically related lithofacies assemblages are recognized each succession consists of a basal sandstone that is the initial accumulation of the lake level rise and lake highstand overlying this sandstone are cyclic evaporite and fine grained clastic deposits of the lake level fall these units are modified by desiccation related processes resulting from lake contraction and desiccation around the lake margins subsequent lake level rise resulted in subaqueous mechanical erosion of clastics and dissolution of interbedded evaporites in more basinward regions dissolution of evaporites occurred prior to accumulation of lake highstand units in the saline lake center the lake never dried up entirely and evidence for partial lake desiccation is equivocal