synmetamorphic high density carbonic fluids in the lower crust evidence from the nilgiri granulites southern india high density co2 inclusions occur abundantly in granulite facies rocks age of metamorphism approximately 2 5 b y of the nilgiri massif southern india the chronology of carbonic inclusions in the widespread enderbitic granulites studied in relation to the development of micro textures and mineral assemblages indicates that randomly oriented negative crystal shaped co2 inclusions 4 20 mu m in garnet and quartz grains qtz i armoured by garnet entrap syn peak metamorphic pore fluids the more abundant trail bound co2 inclusions in the deformed polygonized and partially recrystallized matrix quartz grains qtz ii and iii and plagioclase grains were formed in connection with a stage of compressional deformation and subsequent annealing related to the development of the late proterozoic bhavani shear zone these inclusions resulted from local re equilibration of the former peak granulitic carbonic inclusions and re entrapment of released fluids the presence of pure co2 in all the inclusions is confirmed by microthermometric data and laser excited raman microspectrometry temperatures of homogenization liquid phase are in the range of 50 to 20 degrees c and the corresponding co2 densities are between 1 154 and 0 807 g cm3 mineralogical thermobarometry on the enderbitic granulites documents a continuous gradient of near peak metamorphic conditions from 750 degrees c 9 10 kb in the northern part to 730 degrees c 7 kb in the southwestern part of the nilgiri massif uniform p t estimates 600 650 degrees c 6 7 kb for late coronitic garnet quartz assemblages in enderbites and metadolerites indicate that differential uplift of the massif to mid crustal levels was accomplished before late compressional deformation in conformity carbonic inclusions in quartz ii and iii are characterized by uniformly high density 1 154 1 08 g cm3 in contrast early carbonic inclusions in garnet and quartz i preserve the density contrast reflecting the regional p t gradient during near peak metamorphic fluid entrapment the fluid inclusion systematics indicate near isochoric uplift of the northern high p domain but near isobaric cooling of the southwestern low p domain the carbonic fluids are thought to have been derived either from internal sources during dehydration melting processes or from freezing synmetamorphic intrusives into the lower crust

controls of oil family distribution and composition in nonmarine petroleum systems a case study from the turpan hami basin northwestern china controls on oil family distribution in tectonically complicated nonmarine petroliferous basins are commonly difficult to isolate because of the varying ages of potential source rocks the complex assemblage of organic rich sedimentary facies and the geographic variability of burial histories the turpan hami basin of northwestern china is an oil bearing intermontane basin where stratigraphic sedimentologic and geochemical controls are sufficient to address each of these issues independently and to determine how they influence the current distribution and composition of liquid hydrocarbons source rock age is one of three major statistically significant discriminators affecting oil family composition both lower middle lower or middle jurassic and upper permian rocks are important source rocks for the basin a newly developed diterpane biomarker parameter can distinguish permian rocks and their correlative oils from jurassic coals and mudrocks and their derivative oils source facies is a second key control on petroleum occurrence and character a variety of biomarker parameters that reflect source rock depositional conditions are indexed to rock samples from interpreted depositional environments by erecting rock to oil correlation models the biomarker parameters separate oil families into end member groups group 1 oils lower middle jurassic peatland swamp facies high land plant input less reducing conditions group 2 oils lower middle jurassic profundal lacustrine facies high algal input more reducing conditions and group 3 oils upper permian lacustrine facies high algal stratified anoxic conditions burial history exercises a third major control on petroleum distribution source rock maturation modeling can demonstrate that relatively uninterrupted burial in the asymmetrically subsiding northern turpan hami area taibei depression exhausted upper permian sourced rocks by the late cretaceous which led to southward migration of upper permiansourced oils group 3 into triassic reservoirs of southern and southwestern turpan hami tainan and tokesun depressions subsequent to uplift of the central basin thrust that currently partitions taibei from tainan lower middle jurassicsourced oils were expelled in the taibei depression by paleoceneeocene time which locally charged jurassic and cretaceous reservoirs groups 1 and 2 forming turpan hami s largest oil accumulations in the basin

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

diets and environments of late cenozoic mammals in the qaidam basin tibetan plateau evidence from stable isotopes the timing history and driving mechanisms of c4 expansion and tibetan uplift are hotly debated issues paleoenvironmental evidence from within the tibetan plateau is essential to help resolve these issues here we report results of stable c and o isotope analyses of tooth enamel samples from a variety of late cenozoic mammals including deer giraffe horse rhino and elephant from the qaidam basin in the northeastern tibetan plateau the enamel delta c 13 values are 89 parts per thousand for modern samples and 7 parts per thousand for fossils except for one late miocene rhino cd0722 with delta c 13 values up to 4 1 parts per thousand if the qaidam basin was as arid as today in the mio pliocene these data would indicate that the majority of the animals had c3 diets and only a few individuals besides the exceptional rhino cd0722 may have consumed some c4 plants based on geological evidence however the qaidam basin was probably warmer and more humid during the late miocene and early pliocene than today thus these delta c 13 values likely indicate that many individuals had significant dietary intakes of c4 plants and the qaidam basin had more c4 plants in the late miocene and early pliocene than today moreover the qaidam basin likely had much denser vegetation at those times in order to support such large mammals as rhinos and elephants while the delta o 18 values did not increase monotonously with time the range of variation seems to have increased considerably since the early pliocene indicating increased aridification in the basin the mean delta o 18 values of large mammals and those reconstructed for local meteoric waters display a significant negative shift in the late miocene consistent with the marine delta o 18 record which shows a cooling trend in the same period taken together the isotope data suggest a warmer wetter and perhaps lower qaidam basin during the late miocene and early pliocene increased aridification after the early pliocene is likely due to a combined effect of regional tectonism which resulted in a more effective barrier preventing moisture from the indian ocean or bay of bengal from reaching the basin and global cooling c 2012 elsevier b v all rights reserved

sandstone provenance of north western sectors of the intracontinental cenozoic qaidam basin western china tectonic vs climatic control abstract sandstone samples from all cenozoic formations of the nonmarine internally drained qaidam basin have been collected for provenance analysis to monitor possible changes in sandstone composition driven either by tectonics or climate provided an appropriate hinterland biotite contents may be a reasonable indicator for aridity moderately sorted sandstones with subangular to subrounded grains from the northwestern part of the qaidam basin are immature indicated by a high proportion of feldspars and lithic fragments nevertheless they have relatively high quartz contents of 29 65 averaging between 40 and 45 the average framework compositions of the formations show only a slight variation over time limited to the oldest and youngest cenozoic formations contents of white mica and biotite are significantly higher in upper portions of the section white mica contents increases from 1 0 to 3 7 and biotite from 0 1 to 1 6 respectively this change can be explained by increasing aridity during neogene and surface uplift of altyn mountains and qimantagh which led to higher relief when plotted on basic variation diagrams total quartz feldspar lithic fragments there is a slight shift from continental block field to orogenic field which might reflect the motion of the altyn tagh fault since oligocene times although climate changed during the cenozoic from arid over semiarid back to arid we could not find any distinct changes in the framework mineral compositions over time that could be related to climatic events few selected mudstones from eocene to lower miocene formations have been geochemically analysed by icp ms all samples display uniform high enrichment in light rees in chondrite normalized diagrams with one exception the ree concentrations are decreasing in a stepwise manner although insignificantly from formation to formation with time due to a diluting effect by carbonate

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

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

early to middle jurassic vegetation and climatic events in the qaidam basin northwest china abstract jurassic deposits are well exposed in the qaidam basin qinghai province northwest china and are regarded as one of the most completely developed early middle jurassic plant bearing sequences in northern china the early to middle jurassic palynoflora in this basin shows a high diversity of spores and pollen grains which are characterized by four palynological assemblage zones corresponding to the pliensbachian toarcian aalenian bajocian and bathonian in age vegetation reconstruction demonstrates four vegetation types upland coniferous forest in the pliensbachian coastal cheirolepidiacean forest in the toarcian lowland fern forest in the aalenian bajocian and a mixed forest in the bathonian nearest living relative analysis of the major plant groups shows that the early to middle jurassic vegetation in the qaidam basin not only consists of plants with tropical subtropical climate requirements but also those indicating temperate climatic conditions in addition bryophytes and fungi as well as cheirolepidiaceae which are generally considered to indicate warmer and or drier conditions are also documented in the palynofloras it is suggested that a temperate to subtropical climate generally prevailed during the early to middle jurassic in this basin however the vegetation features and the sedimentary data signify that an overall humid to semi humid phase was punctuated by warmer and locally dry and or arid episodes the two higher temperature and aridity events occurred in the toarcian and bathonian callovian periods in the qaidam basin these climatic events can be inferred by increase of relative abundance of classopollis pollen some tropical subtropical fern spores and the occurrences of variegated red beds and evaporite rocks these events may either be associated in some way with a transient global warming phenomenon due to an enhanced greenhouse effect or be linked with intensification of a potential monsoonal circulation such events finally caused a weakening and even arrested coal accumulation in the qaidam basin during the toarcian and the bathonian callovian intervals

source rock deposition controlled by tectonic subsidence and climate in the western pearl river mouth basin china evidence from organic and inorganic geochemistry abstract interest in factors controlling lacustrine source rock deposition has increased over the last few decades because this type of deposits contain significant petroleum resources generally tectonic subsidence and climate are the two root causes as they control the accommodation potential water column properties and sources of organic matter in this study coupling organic geochemical and elemental geochemical data two potential source rocks i e the eocene wenchang formation e 2 w and oligocene enping formation e 3 e were investigated two models were finally raised to explain deposition of the two set of source rocks according to their paleoclimatic and tectonic properties the source rock potential shows a strong heterogeneity the second member of the eocene wenchang formation e 2 w 2 is characterized by high organic matter content and oil prone kerogen type in contrast the first member of the eocene wenchang formation e 2 w 1 and the oligocene enping formation e 3 e are characterized by low organic matter content and gas prone kerogen type the primary productivity and depositional environment exhibit notable differences between the two potential source rocks horizons and show an obvious variation from the depocenter to the slope and can be best explained by the coevolution of tectonic subsidence and climate during the e 2 w depositional stage low sediment supply led to mudstone deposited in deep lacustrine environment and resulted in underfilled lake basin the low water inflow provided little terrigenous organic matter low bicadinane perylene and floranthene contents and oxygen besides the low area depth ratio impeded the water circulation thus resulted in shallow thermocline and anoxic suboxic bottom environment abundant dibenzothiophene and high c 35 c 31 22s hopane ratios therefore abundant algae which contributed to the high amorphous organic matter aom content can be preserved the warm and wet climate high mn mg ratios gave birth to autochthonous organism such as dinoflagellates and pavlova gyrans abundant 4 methyl sterane during the e 3 e depositional stage the sufficient sedimentary supply resulted in expanding shallow lacustrine and swamp environment the higher area depth ratio and high sediment supply made environment unstable and can be strongly influenced by external environment broader range of mn mg ratios enough terrigenous organic matter tom was transported to the slope but little to the depocenter the slightly hot and dry climate low mn mg ratios led to decreasing autochthonous organism and evaporation environment the shallow water depth and relative dry climate resulted in saline suboxic dysoxic acid bottom environment the co variation of organic and inorganic indexes indicates the combination is a valid method in reconstructing source rock depositional models

multi stage primary and secondary hydrocarbon migration and accumulation in lacustrine jurassic petroleum systems in the northern qaidam basin nw china abstract to improve the understanding on lacustrine jurassic petroleum migration and accumulation in the northern qaidam basin nw china we conduct an integrated analysis of the petrography and geochemistry of oil bearing fluid inclusion including inclusion petrography homogenization temperature combined with reservoir burial and thermal history and reservoir sequential extraction results show that during the first stage of late oligocene to early miocene the deep paleogene reservoir was first charged by oils sourced from middle jurassic rocks petroleum inclusion this charge was accompanied by some oil alteration during the second stage of early to middle miocene the deep paleogene reservoir was charged by lower jurassic sourced oils intergranular free oil and this charging event is different from the first one in that it witnessed little hydrocarbon alteration during the third stage in the pliocene widespread gas sourced from lower and middle jurassic rocks occurred in both the deep paleogene and shallow neogene reservoirs and primary oil accumulations in deep paleogene reservoirs migrated vertically to shallow neogene reservoirs along faults and formed secondary accumulations little alteration took place favorable for the remigration thus the lacustrine lower and middle jurassic petroleum systems in the northern qaidam basin represent multi stage primary and secondary hydrocarbon accumulations and mixing of hydrocarbons was very common

complex patterns of steroidal biomarkers in tertiary lacustrine sediments of the biyang basin china gas chromatography gc gas chromatography mass spectrometry gc ms and gas chromatography mass spectrometry mass spectrometry gc ms ms with co injected synthetic standards were used to analyse the biomarker patterns of some tertiary lacustrine clayey dolomites from the biyang basin china the lithology low pr ph ratio and high gammacerane content of these sediments indicated that high salinity prevailed during their deposition the distributions of steroidal hydrocarbons were particularly unusual and several pseudohomologous series including regular steranes c27 c29 4 methyl steranes c28 c30 including dinosteranes 3b ethyl steranes c29 c31 lanostanes c30 c32 and a variety of other 3b alkylated steranes were identified 3b n propylcholestane 3b n propylstigmastane and 4 4 dimethylcholestane were identified using authentic standards and this is the first time these compounds have been unambiguously characterised in sediments crown copyright 2001 published by elsevier science ltd all rights reserved

origin and accumulation mechanisms of petroleum in the carboniferous volcanic rocks of the kebai fault zone western junggar basin china abstract the kebai fault zone of the west junggar basin in northwestern china is a unique region to gain insights on the formation of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks are widespread in the kebai fault zone and consist of basalt basaltic andesite andesite tuff volcanic breccia sandy conglomerate and metamorphic rocks the volcanic oil reservoirs are characterized by multiple sources and multi stage charge and filling history characteristic of a complex petroleum system geochemical analysis of the reservoir oil hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source the petroleum filling history and the dominant mechanisms controlling the petroleum accumulation reservoir oil geochemistry indicates that the oil contained in the carboniferous volcanic rocks of the kebai fault zone is a mixture the oil is primarily derived from the source rock of the permian fengcheng formation p 1 f and secondarily from the permian lower wuerhe formation p 2 w compared with the p 2 w source rock p 1 f exhibits lower values of c 19 tt c 23 tt c 19 20 tt tt ts ts tm and 20r sterane c 27 c 28 ratios but higher values of tt c 23 c 21 hhi gammacerane c 30 hopane hopane 20s c 34 c 33 c 29 and c 29 20s 20s 20r ratios three major stages of oil charge occurred in the carboniferous in the middle triassic late triassic to early jurassic and in the middle jurassic to late jurassic periods respectively most of the oil charged during the first stage was lost while moderately and highly mature oils were generated and accumulated during the second and third stages oil migration and accumulation in the large scale stratigraphic reservoir was primarily controlled by the top carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity secondary dissolution pores and fractures are the two major reservoir storage space types in the reservoirs structural highs and reservoirs near the unconformity are two favorable oil accumulation places the recognition of the large scale carboniferous volcanic reservoirs in the kebai fault zone and understanding of the associated petroleum accumulation mechanisms provide new insights for exploring various types of volcanic reservoir plays in old volcanic provinces and will undoubtedly encourage future oil and gas exploration of deeper strata in the region and basins elsewhere with similar settings

application of 24 norcholestanes for constraining source age of petroleum abstract two c26 sterane ratios the 24 nordiacholestane ratio ndr and the 24 norcholestane ratio ncr are useful for assessing petroleum source age values for these parameters generally increase in the cretaceous when diatoms were rapidly radiating and further in the oligo miocene due to widespread high latitude deposition of diatomaceous sediments sources with shale lithologies tend to exhibit the highest ratios while carbonate and terrigenous rich lithologies generally show lower ratios on the north slope of alaska elevated ratios are observed for cretaceous hrz oils and mixed oils containing cretaceous input compared to older triassic and jurassic derived oils tertiary sourced oils from romania and bulgaria have much higher ratios relative to jurassic sourced oils in the black sea region oleanane was observed in comparable levels in some black sea tertiary and jurassic oils and source rocks ndr and ncr coupled with other age diagnostic indicators such as oleanane and dinosterane provide powerful tools for differentiating age of source and organic facies for oils from the black sea and sub andean basins of peru and ecuador respectively oils derived from sources deposited in low tropical latitudes tend to have little diatom input and as a consequence do not display high values regardless of age

biomarker signatures of sinian bitumens in the moxi gaoshiti bulge of sichuan basin china geological significance for paleo oil reservoirs abstract chen et al precambrian research 296 1 19 2017 presented a biomarker study on solid bitumens and associated source rock extracts from the moxi gaoshiti bulge of the sichuan basin sw china biomarker characteristics revealed that the solid bitumens and related paleo oils belong to the same group and are well correlated to source rocks of the neoproterozoic dengying and lower cambrian qiongzhusi formations the thermal maturity of solid bitumens and their migration direction have been assessed it appears that these interpretations are internally inconsistent and are also inconsistent with much published geochemical data and the biomarker data are over interpreted and flawed

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

seismic detection of overpressuring and fracturing an example from the qaidam basin people s republic of china abstract shallow hydrocarbon reserves were discovered in 1959 in the nan yi shan structure located in the qaidam basin about 2500 kms west of beijing p r c the first successful deep well encountered an overpressured zone at 3000 meters which resulted in a well blowout to improve the structural definition of the field and delineate the overpressured layer a 3d seismic survey was conducted a region of anomalous seismic time sag associated with fracturing and small quantities of oil and gas was identified on the northwest plunging nose of the nan yi shan anticline velocity dispersion effects were encountered and attributed to localized fracturing in a deeper interval seismic amplitudes were used to identify gas saturated fracture porosity and to describe the spatial limits of overpressuring within this layer this paper will discuss the seismic distortion and unusual velocity signature associated with a localized fracture zone it will demonstrate that with good quality data and sufficient lateral and vertical resolution thin fractured hydrocarbon bearing reservoirs can be delineated and overpressure zones predicted

the origin of 4 methyl steranes and pregnanes from tertiary strata in the qaidam basin china abstract a geochemical study of oils and source rocks in tertiary saline lake facies from the qaidam basin of china demonstrates that pregnanes are mainly derived from the thermal degradation of organic matter in source rocks synchronous with hydrocarbon genesis whereas 4 methyl steranes may principally be a product of microbial activity during diagenesis

suppression of thermal maturity indicators in lacustrine source rocks a case study of dongying depression eastern china abstract the paleogene shahejie formation of the dongying depression in eastern china is a unique region and can offer insights into the suppression of thermal maturity in a large set of successive lacustrine shales this study focuses on the paleogene shahejie formation of n 38 well in the dongying depression the unusual distribution of thermal maturity indicators such as vitrinite reflectance vro and c29 sterane thermal parameters was investigated through geochemical analysis the research interval 2770 3376 m was divided into three parts the upper part of es32 2770 2990 m the lower part of es32 2990 3190 m and the es31 3190 3376 m the es31 mainly contained organic matter type i and some type ii which included mostly good and excellent source rocks meanwhile the upper es32 mainly contained organic matter type iii which included mostly poor and moderate source rocks the parameters g c30h c35h c31 35h c31m c31h c29 20s 20s 20r c31 22s 22s 22r and c32 22s 22s 22r showed a different distribution corresponding to the different lake sedimentary environments various organic facies were developed at the different evolution stages of the lake basin which showed a noticeable influence on the parameters the thermal maturity indicator vro and molecular thermal parameters such as c29 20s 20s 20r c31 22s 22s 22r c32 22s 22s 22r and c31m c31h presented abnormal distributions in the large set of lacustrine shales especially in the es31 this observation suggested suppression of several thermal maturity indicators vro suppression positively correlated well with the corrected hydrogen index and alginite content in maceral composition the high content of alginite group was considered to be the primary reason behind the evident negative vro anomaly

geochemical application of sterane and triterpane biomarkers to a description of oils from the taranaki basin in new zealand abstract the distributions of sterane and terpane biomarkers in a suite of 25 oils from onshore and offshore regions of the taranaki basin of new zealand have been determined by gc ms features of these distributions include the presence of relatively high concentrations of a number of c 24 tetracyclic terpanes the virtual absence of tricyclic terpanes a predominance of c 29 normal iso and dia steranes and the presence of a number of non hopanoid triterpanes in one member of the suite urenui 18 h oleanane is the most abundant component m z 191 ion chromatogram of the terpane class of biomarkers based upon the distributions of 18 h oleanane the mckee and moturoa families of oils can be delineated these terpane distributions are qualitatively similar to those encountered in crude oils from a number of far eastern basins and from the handil field of the mahakam delta indonesia the taranaki oils are of approximately the same thermal maturity maturity parameters calculated from the distributions of c 29 steranes and of 17s h 21 h and 17 h 21s h hopanes confirm recent findings of incomplete nuclear isomerisation in oils derived from tertiary sediments an attempt has been made to correlate the mckee 1 and maui 4 crude oils with potential source rocks from depths of 3708 m and 3825 m respectively the rocks studied have attained insufficient maturity to have been the sources of these oils

magnetostratigraphy of cenozoic deposits in the western qaidam basin and its implication for the surface uplift of the northeastern margin of the tibetan plateau abstract thick cenozoic deposits in the northwestern qaidam basin record erosion of the altyn tagh and high terrain west of that basin and presumably the concurrent growth of the northeastern tibetan plateau a detailed magnetostratigraphic study of the huatugou section northwestern qaidam basin reveals that this section spans the period from 30 to 11 ma magnetostratigraphic and sedimentological studies indicate that the accumulation rate abruptly increased near 15 ma the acceleration in sedimentation rate suggests enhanced tectonic deformation in the qaidam basin since 15 ma that may have begun simultaneously with accelerated deformation along the altyn tagh kunlun and haiyuan faults which contributed to the growth history of the qaidam basin and its surroundings since 15 ma

an organic geochemical investigation of crude oils from shanganning jianghan chaidamu and zhungeer basins people s republic of china abstract eighteen oils from four different oil producing basins in china have been characterized using a variety of organic geochemical techniques the source materials for these oils were deposited under a variety of environmental conditions and this study investigates the use of geochemical parameters in differentiating the resultant oils the parameters discussed are based on relative amounts and distributions of both individual and groups of biomarkers including organosulphur compounds and the carbon isotopic composition of the aliphatic and aromatic fractions examination of the oils showed that those from the zhungeer basin thought to be derived from source rocks formed in a brackish lacustrine environment possessed high concentrations of tricyclic terpanes relative to pentacyclic hopanes and a predominance of 24 methyl and 24 ethylcholestanes c28 and c29 respectively over cholestanes c27 which were virtually absent oils believed to be derived from source rocks deposited in the saline depositional environment of the jianghan basin were characterized by a large amount of gammacerane relative to 17 21 30 homohopanes c31 22r and 22s in general those oils considered to be derived from source rocks deposited in fresh water lacustrine environments shanganning and chaidamu basins had small amounts of tricyclic terpanes relative to pentacyclic hopanes the presence of an unknown c30 pentacyclic terpane small amounts of extended hopanes c31 c35 relative to 17 21 hopane and relatively large amounts of 24 ethylcholestanes 20r and 20s relative to total stearanes it appears therefore that the distribution of biomarkers may be used to differentiate oils derived from different lacustrine environments

maturity effect on carbazole distributions in source rocks from the saline lacustrine settings the western qaidam basin nw china abstract carbazole distributions and biomarker compositions have been investigated in a series of source rocks from the tertiary strata in the western qaidam basin nw china typical biomarker signatures high gammacerane high c 35 hopane and low pr ph indicate a saline lacustrine environment maturity parameter c 29 sterane s s r ranges from 0 06 to 0 58 indicating immature ca 0 35 stages significant variations were observed for carbazole distributions with maturation as for c 1 carbazoles the relative amounts of 1 mc methylcarbazole show a decrease trend in the immature stage and an increase trend in the mature stage while the other three isomers 2 3 and 4 mcs show a generally opposite change indicating a two stage variation as for c 2 carbazole isomers complex variations were observed for their relative amounts an overall increase for 1 7 dmc dimethylcarbazole a slight two stage change for 1 8 and 1 3 dmcs and a marked two stage variation for 2 4 2 5 and 2 6 dmcs comparison of the distributions of carbazole and benzocarbazoles revealed a preferential generation for benzocarbazoles at high maturity levels benzocarbazole ratio a a c varies only in a narrow range 0 52 0 61 in the entire maturity range suggesting limited maturity dependence the results here support the idea that carbazole distributions have strong maturity effect in a wide maturity range and the two stage variations for some pyrrolic nitrogen isomers may indicate their different geochemical controls between the immature and mature stages

geochemical significance of 17α h diahopane and its application in oil source correlation of yanchang formation in longdong area ordos basin china abstract relatively high abundance of 17 h c30 rearranged hopane has been detected in some oils and rock extracts from yanchang formation of longdong area southwestern ordos basin oil shale silty mudstone and carbonaceous mudstone extracts from yanchang formation all have low abundance of c30 rearranged hopane while high concentrations of c30 rearranged hopane were observed in the dark mudstone extracts analysis on the geochemical parameters of the organic matter origin thermal maturity and sedimentary organic facies were carried out the result showed that the depositional redox environment and lithology may be the critical factors for the rearrangement of hopanes which usually occurred in suboxic condition with clay catalyzed reactions as is consistent with the viewpoint of peters and moldowan 1993 according to the relative abundance of diahopane three oil classes can be identified class 1 oil with low abundance of diahopanes was originated from oil shale of chang 7 member while class 2 oil and class 3 oil with middle to high abundance of diahopanes were derived from dark mudstones of chang 4 5 to chang 9 members of yanchang formation of the 151 analyzed oil and extracts samples from different stratigraphic intervals 105 samples belong to class 1 oil coming from oil shale while 46 samples belong to class 2 and class 3 oil derived from mudstones so oil shale of chang 7 member is the main effective source rock of longdong area and dark mudstones of chang 4 5 to chang 9 member are also important source rocks

hydrocarbon generating potential and accumulation contribution of the fourth member of the shahejie formation in the liaodong bay sub basin bohai bay basin abstract the liaodong bay sub basin is one of the most petroliferous sub basins in the bohai bay basin the fourth member of the eocene shahejie formation e 2 s 4 50 5 42 ma which is an important source rock interval in other sub basins was rarely studied in the liaodong bay sub basin the hydrocarbon generating potential biomarker assemblage and accumulation contribution for discovered oil fields of the e 2 s 4 source rock interval in the liaodong bay sub basin were studied using geological and geochemical data the e 2 s 4 source rocks in the liaodong bay sub basin display relatively high total organic carbon contents toc and rock eval hydrogen indices hi and can be considered as a set of excellent oil prone tendency source rocks the source rocks interval is characterized mainly by relatively low pristane phytane pr ph c 19 c 23 tricyclic terpane c 19 c 23 tt c 24 tetracyclic terpane c 26 tricyclic terpane c 24 tet c 26 tt low to medium hopane sterane h s medium 4 methyl steranes c 29 steranes ratio 4 ms c 29 st c 35 22s c 34 22s hopane c 35 c 34 sh and high gammacerane c 30 hopane g h extended tricyclic terpane ratio etr c 28 tt c 29 tt c 28 tt c 29 tt ts and were deposited in anoxic to sub oxic saline water environment with no or minor terrigenous organic matter and medium dinoflagellate input the maturity of e 2 s 4 source rocks in the liaozhong and north liaoxi sags is too high to provide oils for fields the e 2 s 4 source rocks in the south and middle liaoxi sag displayed opportune maturity within the oil window and were proved by oil source correlation having important accumulation contribution for discovered oil fields in this area the e 2 s 4 derived oils should be taken seriously in the future exploration in the south and middle liaoxi sag and on adjacent uplifts

controls of oil family distribution and composition in nonmarine petroleum systems a case study from inner mongolia erlian basin northern china abstract the erlian basin is a continental rift basin located in inner mongolia northern china it is a typical representative of cretaceous northeast asian rift system which includes many small petroliferous basins in mongolia republic and northern china although lower cretaceous source rocks are understood to be most important in the erlian petroleum systems the precise identification of these source rock intervals and their determination on oil families distribution and composition are poorly understood in this tectonically complicated nonmarine basin new bulk data have been gathered from source rock intervals oil sands and crude oil samples in eight main oil producing subbasins geochemical analyses indicate that lower cretaceous aershan formation k1ba and tengger 1 formation k1bt1 are two main source intervals in the erlian basin and their source rock facies vary from profundal lacustrine to marginal lacustrine according to biomarker and trace elements calibration the profundal lacustrine facies is characterised by brackish water and anoxic environment which is similar to their correlative oils family 1 oils the marginal lacustrine facies is characterised by freshwater and suboxic environment which sourced the most common family 2 oils meanwhile different maturation processes exercise the second control on oil groups and their compositions the profundal lacustrine source rocks characterised by their sulphur rich kerogens lead to two oil groups group 1 and group 2 oils whose maturity range from low to normal while the marginal lacustrine source rock only lead to normal maturity oils at last biodegradation affected the composition of a certain oils and formed group 4 heavy oils in addition short migration distance in small subbasins made the contamination or fractionation less notable in the erlian basin

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

jurassic early cenozoic tectonic inversion in the qilian shan and qaidam basin north tibet new insight from seismic reflection isopach mapping and drill core data

the organic geochemistry of the eocene oligocene black shales from the lunpola basin central tibet abstract this paper reports on the depositional paleoenvironment and the potential hydrocarbons of the eocene oligocene black shales from the dingqinghu and niubao formations in the lunpola basin central tibet nineteen samples from two outcrop profiles were analysed the contents of the total organic carbon toc and sulphur were measured other analyses included rock eval pyrolysis solvent extraction and gas chromatography mass spectrometer gc ms the results indicated that the shales from the dingqinghu and niubao formations are thermally immature the pyrolysis data show that the shales contain type i organic matter and that lacustrine algal are the main organic matter sources the low pristane to phytane ratios and the high gammacerane indices indicate that the shales were deposited in a reducing stratified and hypersaline palaeo lake which is consistent with the climate information provided by the development history of palaeo lakes from the eocene to the oligocene epochs

sedimentology organic geochemistry and petroleum potential of jurassic coal measures tarim junggar and turpan basins northwest china lower and middle jurassic coal bearing strata occur widely throughout central asia and are well developed in northwestern china where their thicknesses in the southern junggar northern tarim and turpan basins exceed 2500 2300 and 1500 m respectively examination of these strata along 13 transects across basin margin outcrop belts indicates that they are entirely nonmarine meandering fluvial deposits with local development of braided fluvial and lacustrine deltaic facies chinese subsurface data suggest that regional jurassic lacustrine facies are present down depositional dip consistent with predictions from global circulation modeling of early and middle jurassic monsoonal precipitation laboratory analyses of coals and organic rich shales show a dominance of terrestrial higher plant components visual kerogen analysis indicates that vitrinite inertinite and exinite are the dominant macerals and elemental analysis characterizes most kerogens as type iii rock eval analyses yield moderate hydrogen index values 50 300 and very low oxygen index values 20 jurassic source rock extracts are characterized by odd over even normal alkane distributions high pristane phytane and high hopane sterane ratios dominance of c29 sterane homologs local abundance of diterpenoid compounds and low abundance of tricyclic terpanes geochemical correlation with four petroleums from the junggar tarim and turpan basins strongly suggests that the jurassic coaly deposits and their lacustrine equivalents downdip are petroleum source rocks sterane and hopane distributions of petroleums and extracts of their putative jurassic source rock are similar and can be easily distinguished from published distributions of these compounds in other source rock layers additional correlation parameters include high pristane phytane low abundance or lack of tricyclic terpanes but similar distributions where present and lack of gammacerane with one exception and carotanes compounds that characterize permian and ordovician source rocks and their respective petroleums pyrolysis gas chromatography of selected jurassic samples s ggests that they possess potential for liquid hydrocarbon generation expulsion of c15 hydrocarbons from jurassic source rocks appears likely despite the traditional view that bituminous coals are incapable of expelling long chain hydrocarbons end page 929

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

sheeting and dyking emplacement of the gunnison annular complex sw colorado abstract emplacement of the proterozoic gunnison annular complex colorado involved brittle failure and both subhorizontal sheeting and steeply dipping dyking the annular complex consists of a central diorite body 1730 ma surrounded by a ring of metamorphosed supracrustal rocks in turn ringed by tonalite and granodiorite 1721 ma the older central diorite was emplaced as sills parallel to bedding prior to regional deformation of the gunnison volcanic arc 1730 1710 m y ago this central body was deformed during regional shortening into an upright bowl with inward dipping walls the surrounding country rocks were folded and locally transposed against the central body forming an arcuate foliation conforming roughly to the shape of the body this foliation and bedding acted as mechanical planes of weakness which localized the syn deformational emplacement of the outer ring intrusions as multiple magma sheets parallel to steeply dipping bedding and foliation portions of the outer rings were also injected along concentric inward dipping shear fractures generated under high magma pressure a process similar to cone sheet emplacement in volcanic ring dyke complexes multiple mechanisms were therefore involved in the emplacement of this sheeted annular plutonic complex which otherwise superficially resembles a subvolcanic ring dyke complex