a unique lacustrine mixed dolomitic clastic sequence for tight oil reservoir within the middle permian lucaogou formation of the junggar basin nw china reservoir characteristics and origin abstract the middle permian lucaogou formation in the jimusaer sag of the southeastern junggar basin nw china was the site of a recent discovery of a giant tight oil reservoir this reservoir is unusual as it is hosted by lacustrine mixed dolomitic clastic rocks significantly differing from other tight reservoirs that are generally hosted by marine lacustrine siliciclastic calcitic sequences here we improve our understanding of this relatively new type of tight oil reservoir by presenting the results of a preliminarily investigation into the basic characteristics and origin of this reservoir using field petrological geophysical including seismic and logging and geochemical data field and well core observations indicate that the lucaogou formation is a sequence of mixed carbonate mainly dolomites and terrigenous clastic mainly feldspars sediments that were deposited in a highly saline environment the formation is divided into upper and lower cycles based on lithological variations between coarse and fine grained rocks in particular dolomites and siltstones are interbedded with organic rich mudstones in the lower part of each cycle whereas the upper part of each cycle contains few dolomites and siltstones tight oil accumulations are generally present in the lower part of each cycle and dolomites and dolomite bearing rocks are the main reservoir rocks in these cycles including sandy dolomite dolarenite dolomicrite and a few dolomitic siltstones optical microscope back scattered electron and scanning electron microscope imaging indicate that the main oil reservoir spaces are secondary pores that were generated by the dissolution of clastics and dolomite by highly acidic and corrosive hydrocarbon related fluids

sedimentary record of mesozoic deformation and inception of the turpan hami basin northwest china the turpan hami basin is a major physiographic and geologic feature of northwest china yet considerable uncertainty exists as to the timing of its inception its late paleozoic and mesozoic tectonic history and the relationship of its petroleum systems to those of the nearby junggar basin to address these issues we examined the late paleozoic and mesozoic sedimentary record in the turpan hami basin through a series of outcrop and subsurface studies mesozoic sedimentary facies regional unconformities sediment dispersal patterns and sediment compositions within the turpan hami and southern junggar basins suggest that these basins were initially separated between early triassic and early jurassic time prior to separation upper permian profundal lacustrine and fan delta facies and triassic coarse grained braided fluvial alluvial facies were deposited across a contiguous junggar turpan hami basin permian through triassic facies were derived mainly from the tian shan to the south as indicated by northward directed paleocurrent directions this is consistent with the sedimentary provenance of triassic sandstone mean qm29f29lt42 qp23lvm49lsm28 and qm51p25k24 and conglomerate 32 granitic clasts in the northern turpan hami basin we interpret a relative increase in quartz and feldspar concentration and a relative decrease in volcanic lithic grains in the northern turpan hami basin to reflect unroofing in the tian shan and exposure of late paleozoic granitoid rocks in addition two basinwide unconformities of late permian early triassic and early triassic middle late triassic age attest to deformation within the turpan hami basin and associated continued uplift and erosion of the tian shan

re os geochronology of the lacustrine green river formation insights into direct depositional dating of lacustrine successions re os systematics and paleocontinental weathering abstract lacustrine sedimentary successions provide exceptionally high resolution records of continental geological processes responding to tectonic climatic and magmatic influences these successions are therefore essential for correlating geological and climatic phenomena across continents and furthermore the globe producing accurate geochronological frameworks within lacustrine strata is challenging because the stratigraphy is often bereft of biostratigraphy and directly dateable tuff horizons the rhenium osmium re os geochronometer is a well established tool for determining precise and accurate depositional ages of marine organic rich rocks lake systems with stratified water columns are predisposed to the preservation of organic rich rocks and thus should permit direct re os geochronology of lacustrine strata we present re os systematics from one of the world s best documented lacustrine systems the eocene green river formation providing accurate re os depositional dates that are supported by ar ar and u pb ages of intercalated tuff horizons precision of the green river formation re os dates is controlled by the variation in initial 187 os 188 os and the range of 187 re 188 os ratios as also documented in marine systems controls on uptake and fractionation of re and os are considered to relate mainly to depositional setting and the type of organic matter deposited with the need to further understand the chelating precursors of re and os in organic matter highlighted in addition to geochronology the re os data records the 187 os 188 os composition of lake water 1 41 1 54 at the time of deposition giving an insight into continental runoff derived from weathering of the geological hinterland of the green river formation such insights enable us to evaluate fluctuations in continental climatic tectonic and magmatic processes and provide the ability for chemostratigraphic correlation combined with direct depositional dates furthermore initial 187 os 188 os values can be used as a diagnostic tool to distinguish between lacustrine and marine depositional settings when compared to known oceanic 187 os 188 os values

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

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

simulations of permian climate and comparisons with climate sensitive sediments abstract we use a climate model to simulate two intervals of permian climate the sakmarian ca 280 ma at the end of the major permo carboniferous glaciation and the wordian ca 265 ma we explore the climate sensitivity to various levels of atmospheric co2 concentration and to changes in geography and topography between the two periods the model simulates large seasonality and high aridity in the continental interiors of both hemispheres for both periods the northern summer monsoon weakens and the southern monsoon strengthens between the sakmarian and the wordian owing to changes in geography and topography the northern middle and high latitudes cool in winter between the sakmarian and wordian associated with northward shift of the continents this high latitude cooling strengthens the winter westerlies and shifts the maximum storm track precipitation south in the southern hemisphere the winter westerlies weaken from the sakmarian to the wordian starting the simulations with no permanent i

basin evolution within and adjacent to the tien shan range nw china two late palaeozoic collisions produced the ancestral tien shan range extension following the younger collision preceded a phase of thermal subsidence associated with fluvial and lacustrine sedimentation throughout the jurassic cretaceous and early tertiary this thermal subsidence was interrupted by renewed movement on palaeozoic reverse faults caused by the mesozoic collisions at the southern margin of asia the india asia collision in the early tertiary has produced widespread thrusting in the tien shan which in turn is responsible for the formation of active foreland basins at the southern and northern margins of the range and similar basins within the range itself this compression produced uplift and relief and consequent erosion gave rise to alluvial fans braidplains and ephemeral lakes in an extremely arid environment

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

origin and mixing of crude oils in triassic reservoirs of mahu slope area in junggar basin nw china implication for control on oil distribution in basin having multiple source rocks abstract the origin of crude oils and their varied geochemical features along the western and northern slope of the mahu depression in the junggar basin has been controversial based on the molecular and isotopic geochemistry of hydrocarbons from 46 drill stem test crude oil samples and 36 core samples three oil groups i ii iii and five subgroups i 1 i 2 ii iii 1 and iii 2 have been recognized and oil source correlations have been established the subgroup i 1 oils originated mainly from lower permian fengcheng p 1 f carbonate source rocks subgroup i 2 from p 1 f mudstone source rock and group ii oils from middle permian wuerhe p 2 w mudstone source rock whose potential was underestimated in the past group iii consists of mixed oils i e subgroup iii 1 received contributions from p 1 f carbonates and p 2 w mudstones and subgroup iii 2 is a mixture of oils from p 1 f mudstones and p 2 w generated oils in order to determine the main source rocks the laboratory oil mixing experiments were carried out tricyclic terpane biomarker parameters tts were used to quantify the source contributions whole oil carbon isotope ratios were also used to verify the proportions of different oils in each mixture the results show that subgroup iii 1 oils have diverse mixing ratios in different reservoir subgroup iii 2 oils are mainly from p 1 f mudstones and p 2 w source rock contributes little finally the accumulation process of oil fields along the northern slope of the mahu depression was analyzed and the contributions from different sources were revealed this study provides an effective quantitative method to identify contributions from different lacustrine source rocks to mixed oils in the mahu depression which could be helpful in predicting location and composition of undiscovered oils

what generated the late permian to triassic unconformities in the southern junggar basin and western turpan basin tectonic uplift or increasing aridity abstract the upper permian to triassic sedimentary successions of the southern junggar basin and western turpan basin are characterized by widespread unconformities however the origin of these unconformities remains highly controversial three sections namely the jimsar section in the southern junggar basin and the aiweiergou and yuergou sections in the western turpan basin have been systematically studied using detrital zircon u pb geochronology heavy mineral assemblages and whole rock geochemical analyses detrital zircon ages show that both upper permian and triassic samples from each section have similar age distributions with a major age group at 250 380 ma a subordinate age group at 380 540 ma and sporadic precambrian ages suggesting that the main provenance areas were the north tian shan and the northern margin of the yili central tian shan with a secondary source area in the yili central tian shan ree distributions and trace element crossplots also indicate that upper permian and triassic samples display similar characteristics in both basins all were sourced from felsic or mixed mafic felsic rocks with only a minor component of ancient or recycled sediments detrital provenance and geochemical analyses agree in showing no significant changes in the source to sink sediment transport system from the late permian to the triassic however field observations heavy minerals analysis and geochemistry do suggest that both the southern junggar basin and western turpan basin experienced an arid climate during this interval both upper permian and triassic sediments in the two basins contain abundant hematite display low cia values and th u ratios and have mudcracks redbeds and other indicators of arid climate therefore we suggest that the regional unconformities in the two basins were not generated by regional tectonic uplift but most likely resulted from an increasingly arid climate

subaqueous shrinkage cracks in the devonian of scotland reinterpreted abundant lenticular straight to curving cracks on bedding planes are commonly interpreted as subaqueously formed shrinkage cracks syneresis cracks the two most influential examples being those in the green river formation picard 1966 and the devonian orcadian basin of scotland donovan and foster 1972 cracked surfaces in the orcadian basin deposits show all gradations between lenticular cracks and well developed polygons of subaerial origin some lenticular cracks are inferred to have formed during subaerial desiccation many of the simplest lenticular cracks also have the shapes of gypsum crystals and originated as pseudomorphs the gypsum crystals were often important in providing nuclei for later desiccation cracks more complex crack patterns of incipient to fully formed desiccation polygons have arisen from desiccation of surfaces containing gypsum crystals or pseudomorphs resulting from gypsum crystal dissolution cracks of all types are preserved by sand infills introduced by wind transport across dried up lake floors reassessment of the literature reporting subaqueous cracks in rocks shows that many of these cracks are likely to have originated in a similar way partly as gypsum crystals and partly by limited subaerial desiccation the remaining examples have either already been reinterpreted in other ways or are insufficiently documented to rule out a subaerial origin there is no clear evidence for subaqueously formed cracks being preserved in rocks

integrated provenance analysis of a complex orogenic terrane mesozoic uplift of the bogda shan and inception of the turpan hami basin nw china we employ petrographic and advanced geochemical tech niques to better document the evolution of the turpan hami basin based on the unique geologic histories of the arc terranes that served as potential sources of turpan hami deposits first a provenance study of permian through cretaceous sandstone of the turpan hami basin reveals temporal and spatial changes in dominant source ter ranes that provided detritus to the basin volcanic lithic rich upper permian sandstone mean qm 19f18lt63 q p 7lvm89lsm4 q m 48p39k13 followed by more quartzose compositions in triassic sandstone mean qm 41f19lt40 q p 20lvm75lsm5 q m 68p21k11 indicate progressive un roofing of the extinct northern and central tian shan arc terranes to the south of turpan hami a sharp change to sedimentary lithic rich lower jurassic sandstone mean qm 47f16lt37 q p 16lvm42lsm42 qm 75p12k13 overlain by a return to volcanic lithic rich middle ju rassic sandstone mean qm 39f21lt40 q p 14lvm51lsm35 q m 65p21k14 points to the initial uplift and unroofing of the largely andesitic bogda shan to the north which first shed its sedimentary cover as it emerged to become the partition between the turpan hami and southern jung gar basins second geochronological trace element and sm nd isotopic varia tions among granitoids in the late paleozoic tian shan orogenic belt provide a further test of mesozoic uplift of the bogda shan on the basis of previous models of crustal compositions throughout the south central and north tian shan bogda shan and east and west jung gar terranes we infer that isotopically enriched granitic cobbles av erage endi 5 20 50 n 5 6 contained in lower triassic deposits in the north central turpan hami basin were derived from the continen tal crustal central tian shan terrane south of turpan hami and not from the more oceanic north tian shan bogda shan and east and west junggar terranes north of the turpan hami basin we therefore infer that the ancestral bogda shan had not been uplifted by the early triassic and that prior to this time a unified junggar turpan hami basin existed during late permian deposition of extensive lacustrine deposits

geologic characteristics of hydrocarbon bearing marine transitional and lacustrine shales in china abstract organic rich shales spanning in age from pre cambrian to quaternary were widely deposited in china this paper elaborates the geology and unique characteristics of emerging and potential hydrocarbon bearing shales in china the pre cambrian sinian doushantuo to silurian black marine shales in the intra shelf low to slope environments were accumulated in south china and tarim platform in northwest china these marine shales with maturity ro of 1 3 5 are in dry gas window during carboniferous to permian the shales associated with coal and sandstones were mainly deposited in coastal swamp transitional setting in north china ne china nw china and yangtze platform in south china these transitional shales are generally clay rich and are potential gas bearing reservoirs since middle permian the lacustrine shales with total carbon content toc up to 30 and ro mainly in oil window are widely distributed in all the producing basins in china the lacustrine shales usually have more clay mineral content than marine shales and are characterized by rapid facies change and are interbedded with carbonates and sandstone the high quality shale reservoir with high toc hydrocarbon content and brittle minerals content is usually located at transgressive systems tract tst to early highstand systems tract ehst interval deposited in anoxic depositional setting recent commercial shale gas production from the silurian longmaxi marine shale in the southeastern sichuan basin preliminary tight oil production associated with lacustrine hydrocarbon bearing shale intervals and hydrocarbon shows from many other shales have proven the hydrocarbon bearing shales in china are emerging and potential shale gas and tight shale oil plays tectonic movements could have breached the early hydrocarbon accumulation in shales and tectonically stable areas are suggested to be favorable prospects for china shale plays exploration and production

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

provenance and depositional conditions of fluvial conglomerates and sandstones and their controlling processes in a rift setting mid permian lower and upper quanzijie low order cycles bogda mountains nw china abstract this study investigates how provenance lithology transport distance and depositional and paleoclimatic conditions had affected the composition and texture of fluvial conglomerates and sandstones in the middle permian lower and upper quanzijie low order cycles bogda mountains greater turpan junggar intracontinental rift basin nw china composition and texture of gravels in conglomerates and sandstones define two conglomerate and two sandstone petrofacies respectively in tarlong taodonggou area in southern bogda and dalongkou area 70 km to the north in northern bogda conglomerate petrofacies i occurs in tarlong taodonggou and is dominated by basaltic gravels whereas conglomerate petrofacies ii occurs mainly in dalongkou and is dominated by sedimentary gravels sandstone petrofacies i occurs in tarlong taodonggou and contains dominantly basaltic lithics few sedimentary lithics and minimal quartz it is compositionally immature and texturally immature to submature the compositional maturity increases upsection conglomerate petrofacies i and sandstone petrofacies i both indicate the young tian shan arc to the south as the main sediment source and rift shoulders as a local source sandstone petrofacies ii occurs in dalongkou and contains dominantly sedimentary lithics and abundant and well developed pedogenic clay coats the petrofacies in dalongkou indicate older rift sedimentary rocks exposed at rift shoulders as the main sediment source and distant suture zones as a minor source in summary the composition and texture of quanzijie conglomerates and sandstones are mainly controlled by provenance lithology and secondarily depositional and paleoclimatic conditions and transport distance the results substantiate the rift origin of the turpan junggar basin in middle permian which had many half grabens and grabens and was bordered by a volcanic arc at the southern basin margin

hydrocarbons from non marine source rocks abstract non marine source rocks make a significant contribution to the world s oil reserves they are particularly important as source rocks in china australia new zealand and indonesia non marine mainly lacustrine oil shales from deposits in a number of locations were collected for study samples from thailand mae sot and mae moh yugoslavia aleksinac u k lothians caithness bituminous flagstone brora skye and france autun were analysed in addition coals from the mahakam delta in indonesia and from australia and some boghead coals from a number of deposits were also analysed along with green river and messel shale samples for comparison hydrocarbon characterisation was performed mainly by thermal extraction and pyrolysis gas chromatography gas chromatography of oils produced by hydrous pyrolysis was also performed estimation of maturity was based mainly on vitrinite reflectance and spore fluorescence there are considerable differences in hydrocarbons produced by pyrolysis of the samples from the different deposits paraffinic hydrocarbons are generated in abundance by all samples in the boghead coals hydrocarbons are mostly paraffinic in the humic coals aromatics are as prominent as paraffinic hydrocarbons in the lacustrine shales and carbonates paraffinic and isoprenoid hydrocarbons vary in abundance and isoprenoids are very abundant in some of the carbonates the thermal extracts indicate that in most cases hydrocarbon generation has not started the presence of a number of homologous series in some of the immature lacustrine samples is interpreted to be related to the abundance of alginite the early generation of acyclic isoprenoid hydrocarbons as well as aromatics relative to straight chain hydrocarbons is indicated by the hydrous pyrolysis results in the case of the green river oil shales it may be an additional reason for the lack of n alkanes in early migrated bitumens found in the green river basin area along with biodegradation

sedimentary and organic geochemical investigation of tertiary lacustrine oil shale in the central tibetan plateau palaeolimnological and palaeoclimatic significances article i nfo the zhuonai lake and lunpori oil shale located in the central tibetan plateau were deposited in a tertiary lacustrine environment in the hoh xil and lunpola basins respectively a combined investigation of sedimentary organic geochemistry and organic carbon isotope was performed to define source rock potential the palaeoenvironment and source of the organic matter three types of facies sequences are developed in the zhuonai lake section and oil shale mainly occurs in the oil shale marl sequence the oil shale silty claystone and oil shale marl facies sequences are developed in the lunpori section both oil shales are finely stratified especially for the lunpori oil shale with thickness of the laminae about 10 m which contains abundant pyrite crystals and fossilized fish bones both the zhuonai lake and lunpori oil shale contain high values of total organic matter toc s2 and hydrogen index hi indicating the oil shales have good oil source rock potential tmax values show an immature stage of organic matter for the zhuonai lake oil shale and thermally marginally mature for the lunpori oil shale because of difference in their burial history lunpori oil shale shows the characteristics of amorphous organic matter aom dominance odd over even predominance maximum n alkanes peak at nc25 or nc23 higher proportion of c29 sterane light 13 corg values 30 0 to 27 4 high concentrations of phytane pr ph ratio ranging from 0 02 to 0 18 high values of gammacerane index up to 25 26 and presence of carotane which are consistent with a reducing stratified and hypersaline palaeo lake with main contribution of algae and bacteria to the organic matter om oil shale samples from the lower and upper part of the zhuonai lake section are characterized by low h c ratios and high o c ratios amorphous humic om and vitrinite dominance odd over even predominance with long chain n alkanes dominance heavy organic carbon isotope and c29nc27 sterane distribution in agreement with a main contribution of land plant the heavy organic carbon isotope suggests the expanding of c4 land plant during the early miocene while the most samples show characteristics of aom dominance maximum peak at nc29 or nc31 and high c27 sterane concentration consistent with a main contribution from algae to the om the pr ph ratio cannot be applied as a measure for redox conditions in the section because of maturity effects biomarker analysis indicates that the salinity during the deposition of the zhuonai lake oil shale was not enhanced the oligocene lunpori oil shale and the early miocene zhuonai lake oil shale recorded the variation of palaeolimnological water chemistry the development history of the palaeo lakes from the oligocene saline to the early miocene fresh water reflects the variation of palaeoclimate from dry to humid in the central tibetan plateau

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

multiple phase tectonic superposition and reworking in the junggar basin of northwestern china implications for deep seated petroleum exploration the junggar basin is one of the major petroliferous basins in northwest china where deeper hydrocarbon exploration has become an inevitable trend for resource development in this paper the structural features and tectonic evolution of the junggar basin are discussed based on seismic profiles drilling data isochore maps and additional balanced cross sections our results suggest that the basin has undergone five extension to compression stages of tectonic evolution since the permian the junggar basin initially developed from several isolated continental rifts in the early permian at the beginning of the middle permian the basin developed into a more integrated terrigenous lake basin with the deposition of fine grained organic rich lacustrine sediments the basin inverted during the late permian compressional uplifting then the sedimentary basin was superimposed and reworked by episodic mesozoic to cenozoic tectonic events giving rise to the uplift and erosion at the basin margins while folding or tilting within the basin at present the basin presents a wedge shaped geometry with thickest strata in the south and thinnest strata in the north the presence of source rocks reservoirs regional seals and traps is closely related to the multiphase basin scale extension to compression tectonic cycles of the basin episodic tectonic movements are also responsible for the adjustment and destruction of earlier formed hydrocarbon pools and the formation of secondary pools the preferential accumulation sites for prospective deep seated petroleum exploration are also proposed

molecular and carbon isotopic geochemistry of crude oils and extracts from permian source rocks in the northwestern and central junggar basin china abstract the junggar basin is a major oil producing province in china most oil reservoirs found so far in this basin are in the mahu sag and neighboring uplifts northwestern junggar basin a total of 78 oils and 10 permian source rocks from the northwestern and central junggar basin and two oils and two permian source rocks from the eastern junggar basin were analyzed by gc gc ms and gc irms the 78 oils can be clearly classified into two groups based on these analytical results for group i oils 13c values of individual n alkanes are relatively higher and remain stable with increasing carbon number for group ii oils these values are relatively lower and decrease at first and then increase with carbon number differences in molecular parameters can be also observed between these two groups of oils group i oils generally have 1 higher pr n c17 and ph n c18 ratios and lower pr ph ratio and 2 higher gammacerane c30 hopane gammacerane and carotane carotane c30 hopane ratios compared with group ii oils in addition group i oils mainly have tricyclic terpane distribution patterns with either c20 c21 c23 while group ii oils mainly have the pattern of c20 c23 however molecular parameters overlap to some extent between these two groups of oils group i oils correlate well with the nine source rocks of the lower permian fengcheng formation p1f while group ii oils correlate well with the three source rocks of middle permian age based on carbon isotopic and molecular compositions the occurrence of these two groups of oils in the northwestern and central junggar basin are consistent with facies and thickness variations in the source rocks within the lower permian fengcheng formation p1f and middle permian lower wuerhe formation p2w

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

paleomagnetic results from late paleozoic dikes from the northwestern junggar block northwestern china abstract paleomagnetic data have been obtained from late paleozoic mafic and silicic dikes in northwestern junggar a triangular fragment of early to middle paleozoic trapped oceanic crust located between the kazakhstan tarim and siberian blocks discordance between the observed declination and expected declinations from tarim and kazakhstan suggests a 30 40 counterclockwise tectonic rotation of the sampling region relative to tarim and kazahkstan this rotation is attributed to post triassic thrust and strike slip faulting at face value there is a good agreement between the observed mean inclination and those expected from kazakhstan and tarim tectonic interpretation of this mean inclination is obscured by a large difference in inclination from two sampling localities a combination of geomagnetic secular variation and local tilt of fault block may cause this dispersion

origin of beatrice oil by co sourcing from devonian and middle jurassic source rocks inner moray firth united kingdom commercial hydrocarbons in the moray firth area of the north sea occur in reservoirs ranging in age from devonian to tertiary with the bulk of the reserves located in upper jurassic and lower cretaceous clastic rocks most hydrocarbon discoveries in this area have been made in the outer moray firth primarily in the witch ground graben a single oil field beatrice has been developed in the inner moray firth area the unusual location and chemical composition of beatrice compared to piper and other north sea oils generated from the kimmeridge clay have contributed to the longstanding controversy on its origin oil source potential in the inner moray firth has been recognized in lacustrine devonian dolomitic siltstones middle jurassic paralic coals upper jurassic marine shales and other rocks however prior to this study only the upper jurassic kimmeridge clay was recognized as a significant effective source rock in the main graben area of the north sea biomarker and stable carbon isotope analyses conclusively show that beatrice oil could not have been generated from the classic kimmeridge clay source rock but is a mixture of products derived from effective devonian and middle jurassic source rocks this work demonstrates the power of a multiparameter geochemical approach in solving this difficult oil to source rock correlation problem use of this approach can lead to the recognition of new exploration plays in previously well explored basins

organic geochemistry and elements distribution in dahuangshan oil shale southern junggar basin origin of organic matter and depositional environment abstract the dahuangshan oil shale located in the northern bogda mountain on the southern margin of the junggar basin was deposited in a late permian lacustrine environment a combined investigation of element and organic geochemistry was performed to define the source rock potential the paleoenvironment and source of the organic matter thick sequences of oil shales with an average thickness of 638 m were deposited in lucaogou formation which mainly consists of oil shale argillaceous dolomite silty claystone tuff limestone and dolomitic marl a spot of plant stem fossils and abundance of pyrite crystals fishtail and fish skeleton can also be found there analyzed oil shale samples from dahuangshan area are characterized by high total organic carbon toc contents 5 6 34 75 s2 22 65 199 25 mg hc g rock hydrogen index hi 359 1068 mg hc g toc and oil yield 4 9 26 6 indicating the oil shales have excellent source rock potential tmax values 433 453 c show an early to medium maturation stage of organic matter which is supported by organic geochemical maturation parameters all of the obtained kerogen types are types ii and i with oil prone source rock potential dahuangshan oil shale samples are rich in sio2 68 59 followed by al2o3 10 18 and fe2o3 5 43 compared with average shale and north american shale composite nasc analyzed oil shale samples are obviously enriched in p 0 71 there is a significant correlation between al2o3 and fe2o3 mgo k2o mno cu ba co and ni for their association with clay minerals besides the significant correlations between fe2o3 and mno co and ni are considered to result from their similarity on geochemical behavior all selected oil shales are characterized by distinctly sloping light rare earth elements lree trends lan smn 2 70 5 95 accompanied by flat heavy rare earth elements hree trends with distinct eu negative anomalies 0 60 0 73 two slightly different patterns of rees in the oil shale samples are distinguished by the difference in ce depletion and nd anomaly in addition dahuangshan oil shale samples are characterized by short to middle chain n alkanes low carbon preference index cpi values 0 93 1 24 single peak composed of nc20 or nc22 low pr ph 0 41 0 91 relatively high homohop index 0 061 0 99 and high concentrations of c27 sterane indicating reducing deep water and moderate saline environment with prevalent contribution of algae and microorganisms to organic matter accumulation

genetic classification of petroleum systems our genetic classification of petroleum systems is founded on a simple working nomenclature that consists of combining qualifiers from each of the following three categories 1 charge factor supercharged normally charged or undercharged 2 migration drainage style vertically drained or laterally drained and 3 entrapment style high impedance or low impedance the charge factor is estimated on the basis of the richness and volumetrics of mature source rocks the source potential index spi which combines source rock richness and thickness into a single parameter is a convenient shortcut for comparing the petroleum potential of diverse source rocks containing dissimilar kerogen types and for rapidly estimating regional charging capacity in extensively explored basins a positive correlation exists between the magnitude of spi and basin wide petroleum reserves the migration drainage style is determined from the structural and stratigraphic framework of a basin vertical migration drainage which occurs mainly through faults and fracture systems breaching a seal is characteristic of petroleum systems contained within rift basins deltaic sequences salt dome provinces wrench basins and fold and thrust belts in contrast lateral migration drainage is dominant wherever stratigraphically continuous seal reservoir doublets extend over a very large area in a tectonically stable province e g commonly foreland or intracratonic platform basins recognition of the dominant migration style helps to predict the location of zones of petroleum occurrence in relation to the hydrocarbon kitchens the entrapment style which is also dependent on the structural framework and the presence and effectiveness of seals describes the degree of resistance i e impedance working against dispersion of the petroleum charge application of these working concepts should help to significantly reduce geologic risk particularly in new ventures type exploration

late paleozoic paleomagnetic results from the junggar block northwestern china we have obtained middle carboniferous to permian paleomagnetic results from the junggar block in order to test its tectonic coherence and to reconstruct its late paleozoic position from hoboksar on the northwestern margin of junggar a paleomagnetic pole from basic silicic flows yields p 299 e p 70 n n 15 sites k a95 36 6 4 in the same general area a pole from lava flows plutons and as well as from remagnetized limestones sandstones is at p 350 e p 69 n n 26 site k a95 15 7 5 farther to the southwest in keramayi a pole from late paleozoic dike swarms lies at p 230 e p 80 n n 23 sites k a 95 16 7 8 in the southern margin near urumqi from sedimentary rocks and volcaniclastics of the middle to upper carboniferous qijiagou and aoertu formations a pole is produced at p 7 e p 72 n n 15 sites k a95 28 7 4 from the middle carboniferous liushugou formation and dike swarms intruding into the formation two poles are located at p 231 e p 69 n n 4 sites k a95 46 13 7 and p 172 e p 55 n n 7 sites k a95 17 15 1 respectively though reliabilities of these two poles are in question magnetic polarities of all the poles in our study are exclusively reversed based on positive fold tests and a baked contact test we believe that these magnetizations were acquired during the kiaman reversed interval 250 320 ma more accurate ages of the magnetizations cannot be resolved at present despite widely separate locations the pole positions are roughly located on a small circle segment around the junggar block similar inclinations suggest a coherent junggar block since permian time based on the results of this study and other published paleomagnetic data a mean middle carboniferous to permian paleomagnetic pole is calculated at p 329 e p 82 n n 6 poles k a95 26 13 4 recognition of late paleozoic apparent polar wander for junggar is obscured by a lack of detailed geochronologic data and possible relative horizontal rotations around vertical axis the paleolatitude for the southern junggar predicted by this pole is only 4 south of the present latitude difference exists between the mean pole from junggar and permian poles from other tectonic units in asia tarim siberia kazakhstan and north and south china indicating post permian relative motions at the boundary between tarim and junggar this motion is likely to have a left lateral sense

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

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

a new method for assessing tight oil with application to the lucaogou formation in the jimusaer depression junggar basin china this study proposes a new method for estimating tight oil resources in a closed petroleum system using an alternative mass balance model the proposed approach primarily derives resource estimates based on a large volume of rock eval pyrolysis data in addition to leveraging the cost effective straightforward and rapid process the proposed method has the flexibility to assess the potential of different types of resources including organic rich tight shale oil and organic lean tight oil the method is validated by assessing the oil resource potential of the middle permian lucaogou formation p2l in the jimusaer depression junggar basin china results indicate that the p2l contains 1 62 109 t 11 91 109 bbl of organic rich and 2 88 109 t 21 17 109 bbl of organic lean tight oil of the organic rich tight oil 21 comprises free oil resources amounting to 0 343 109 t 2 521 109 bbl the proposed approach deals sufficiently with the different resources in a petroleum system well and provides a useful tool for estimating the resource potential of an unconventional play

hydrocarbon generation potential of triassic mudstones in the junggar basin northwest china triassic mudstones in the junggar basin of northwest china especially those of the upper triassic baijiantan formation which formed during a lake flooding event are the most important set of cap rocks in the basin these mudstones presumably have hydrocarbon generation potential although this potential has not been documented here we provide new organic geochemical and geological background data on these mudstones and discuss their hydrocarbon generation potential geochemical analyses were performed on available samples collected from more marginal shallow lake facies in the central basin area these analyses indicated that these rocks contain about 1 0 total organic carbon toc the organic matter type is predominantly type iii kerogen derived mainly from terrestrial higher plants the organic matter underwent maturation in uplifted areas and reached higher maturity levels in depressions within the basin thus the triassic mudstones may have a potential for hydrocarbon generation during the lake flooding period especially for gas and hence deserve attention in future exploration more research needs to be conducted on the generation potential of these units including oil besides gas as few deep lake facies samples from depressions in the basin are currently available for investigation

polycyclic alkanes in a biodegraded oil from the kelamayi oilfield northwestern china abstract a comparison is made of the distributions of certain classes of saturated hydrocarbon biomarkers in an unaltered oil and a severely biodegraded oil from the kelamayi oilfield in the zhungeer basin of northwestern china both oils are thought to have the same source rock the n alkanes acyclic isoprenoids carotenoid derived alkanes and regular c27 c29 steranes which are present in the nondegraded oil were not detected in the biodegraded sample additionally the biodegraded oil shows an increase in the abundance oil and the presence of 17 h 25 norhopanes 17s h 25 norhopanes c 10 demethylated tricyclic terpanes and a c 10 demethylated c23 tetracyclic terpane which were not detected in the nondegraded oil c26 and c25 regular steranes appear to show a much greater resistance to microbial attack than the c27 c29 regular steranes as indicated by an isomer distribution for these low molecular weight steranes that is expected for nondegraded samples in the biodegraded oil unknown tricyclic compounds showing a base fragment ion of m z 219 and a similar carbon number abundance to the steranes in the nonbiodegraded sample are present in relatively high concentrations in the biodegraded oil these compounds are also present in very low abundance in some nondegraded oils from the kelamayi basin indicating that their much higher concentration in the microbialy altered oil is possibly due to their resistance to biodegradation however at present their derivation from the microbial alteration of steranes cannot be ruled out several series of bicyclic compounds are also present in higher concentrations in the biodegraded oil

organic geochemistry of carboniferous source rocks and their generated oils from the eastern junggar basin nw china abstract carboniferous source rocks have been gaining increasing attention after the discovery of the kelameili gasfield in the eastern junggar basin in 2005 two sets of source rocks within the lower carboniferous dishuiquan formation c 1d and upper carboniferous batamayineishan formation c 2b respectively have been identified in this area in this paper clear differences between these two source rocks are demonstrated in molecular and carbon isotopic compositions the c 1d source rocks in comparison with the c 2b source rocks have remarkably lower pr n c 17 ratio higher ts ts tm and c 30 diahopane c 30 diahopane c 30 hopane ratios lower concentration of c 24 tetracyclic terpane relative to c 23 and c 26 tricyclic terpanes and higher gammacerane c 31 hopane ratio 13 c values of individual n alkanes decrease with carbon number for c 1d source rocks while the opposite is true for c 2b source rocks among the 10 oils collected from the studied area four were generated exclusively from c 1d source rocks while the others were mainly derived from c 1d source rocks but contaminated by a small or trace amount of oil components which were derived from the c 2b middle permian pingdiquan formation p 2p and lower jurassic source rocks the free adsorbed and inclusion oils from three oil containing volcanic reservoir rocks within the c 2b formation generally correlate with c 1d source rocks based on molecular and carbon isotopic data however the three types of oil from the same reservoir rock vary significantly in molecular and carbon isotopic compositions reflecting facies and maturity changes of charging oil during the reservoir filling

upper permian lacustrine organic facies evolution southern junggar basin nw china abstract the jingjingzigou lucaogou and hongyanchi formations of the southern junggar basin together comprise over 1000 m of organic rich lacustrine facies they record an overall evolution from relatively shallow evaporative lakes to freshwater lakes associated with fluvial systems the jingjingzigou formation is characterized by low toc and hi and biomarker features such as abundant carotane consistent with a specialized saline or hypersaline biota biomarker distributions in jingjingzigou formation extracts most closely resemble oils from the giant karamay oilfield the lucaogou formation represents one of the richest and thickest lacustrine source rock intervals in the world yet it contradicts conventional lacustrine source rock models in at least two important aspects first deposition occurred at middle paleolatitudes 39 43 n rather than in the tropics second limited nutrient supply in a drainage basin dominated by intermediate volcanic rocks appears to have caused low to moderate primary productivities stable salinity stratification and low inorganic sedimentation rates in a deep lake nonetheless resulted in deposits with up to 20 toc and hi near 800 the overlying hongyanchi formation has 1 5 toc but low hi and was deposited in freshwater oxic to sub oxic lakes

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

petroleum generation kinetics for permian lacustrine source rocks in the junggar basin nw china abstract the junggar basin is a major oil producing province in china most of the oil originated from permian lacustrine oil prone source rocks in the basin kinetic parameters for oil and gas generation were obtained from confined pyrolysis experiments using gold capsules at heating rates of 20 c h and 2 c h on kerogen samples from two permian lacustrine oil prone source rocks j23s3 and ss1s3 having hydrogen indices of 663 and 698 mg hc g toc respectively the kinetic properties for oil and gas generation vary substantially between these two source rocks assuming a burial heating rate of 5 c my the temperature for 50 transformation ratio to oil is 132 c for j23s3 and 168 c for ss1s3 the maximum oil yields are about 604 and 770 mg g toc while the maximum yields of total gaseous hydrocarbons are about 306 and 348 mg g toc for j23s3 and ss1s3 respectively gaseous hydrocarbons from the confined pyrolysis experiments include primary cracking components from kerogen and secondary cracking components from the generated oil the secondary cracking gaseous hydrocarbons comprise up to 84 9 and 95 1 of the total respectively for the two source rocks in the highest temperature experiments a practical method estimates the amount of gaseous hydrocarbons generated from these source rocks under geological conditions based on 1 kinetic parameters for gas generation obtained from kerogen confined pyrolysis experiments in the present study 2 the maximum yield of gaseous hydrocarbons from oil confined pyrolysis experiments from previous studies and 3 the maximum amount of expelled oil the maximum amounts of expelled oil range from 509 588 and 724 750 mg g toc with oil expulsion efficiencies in the ranges 84 3 97 4 and 94 0 97 4 for j23s3 and ss1s3 respectively assuming that the amounts of retained oil range from 30 160 and 50 110 mg g toc for the two source rocks after oil expulsion based on the amounts of extracted bitumen consequently the maximum yields of total gaseous hydrocarbons could be in the ranges 53 1 87 0 and 25 5 36 8 mg g toc respectively for j23s3 and ss1s3 in nature using the kinetic parameters for these two source rocks determined from pyrolysis experiments oil and gas generation and expulsion were modeled for source rocks within the lower permian fengcheng p 1f and middle permian lower wuerhe formations p 2w in the central area of the mahu depression the source kitchen for most oilfields in the basin

an automated method for the interpretation of magnetic vertical gradient anomalies the use of airborne magnetic vertical gradient surveys is increasing interpretation however is mostly used qualitatively as an aid to geologic mapping presently quantitative interpretation techniques are based on the analysis of isolated anomalies in this paper we develop a numerical method for interpreting the magnetic vertical gradient anomalies of dipping dikes and planar geologic contacts the method is based on a linearization of the equations describing these anomalies the solution can be used to interpret isolated anomalies or whole profiles in a werner style deconvolution using data from the val d or mining area canada we have calculated magnetic models to test the interpretation technique magnetic vertical gradient profiles calculated from the interpreted models closely match the observed data

comment on georgiev et al structure and u pb zircon geochronology of an alpine nappe stack telescoped by extensional detachment faulting kulidzhik area eastern rhodopes bulgaria in this discussion we evaluate the field chemical sedimentary structural and metamorphic data related to the kulidzhik area tectonic proposal

origin and mechanism of the formation of the low oil saturation moxizhuang field junggar basin china implication for petroleum exploration in basins having complex histories the moxizhuang field is a small oil field in the central junggar basin containing several low saturation low resistivity oil reservoirs which display a complex correlation between oil saturation and porosity and permeability that is atypical of both the filled and drained reservoirs biomarker associations of crude oil and grains containing oil inclusions gois of both the present day water bearing zones water zones and the oil and water bearing zones low oil saturation pay zones were analyzed to investigate the mechanisms for the formation of the low saturation low resistivity oil accumulations the biomarker assemblage and hierarchical cluster analysis indicate that oil in the moxizhuang field was mostly generated from permian source rock deposited in brackish to hypersaline anoxic environments the pay zones and several water zones display goi values as much as 38 greater than the generally accepted threshold goi value for an oil column 5 these goi values are similar to those for high saturation oil reservoirs in the bohai bay basin and oil zone samples from australian basins suggesting that both pay zones and water zones were high saturation oil reservoirs in the geologic past geologic history analysis shows that the moxizhuang field was located on the north wing of a paleoanticline during oil charge in the late cretaceous to paleogene this anticline has gradually evolved into a south dipping monocline since the neogene causing northward remigration of accumulated oil differential lateral leakage of accumulated oil in different sandstone layers during the remigration phase led to the formation of the water zones with high goi values completely drained reservoirs and the low saturation low resistivity pay zones partially preserved reservoirs and caused the complex correlation between oil saturation and porosity and permeability compared with other postaccumulation physicochemical alteration processes lateral leakage has rarely been recognized recognizing differential lateral leakage of accumulated petroleum with the existence of high quality unfaulted cap rocks has important implication for petroleum exploration in sedimentary basins having complex evolution histories

geochemical characteristics palaeoenvironment and formation model of eocene organic rich shales in the beibuwan basin south china sea abstract lacustrine organic rich shales in the eocene are the most important source rock in the beibuwan basin palynological petrographical and geochemical data were applied to define their palaeoenvironment formation and petroleum potential toc values range from 2 84 to 14 77 and the kerogens of these dark gray or brown shales with numerous lamalginites can be classified as oil prone type i and type ii1 biomarkers are characterized by a high abundance of c30 4 methylsteranes a low content of oleanane and diterpanes relatively abundant pentacyclic terpanes which indicate that the organic matter in the shales is typically algal and microbial origin abundance of amorphous organic matter the presence of low level gammacerane small amounts of pyrite pr ph ratios of 1 38 2 42 and v v ni ratios of 0 74 0 84 suggest that the organic rich shales were formed in a less oxic to anoxic stratified fresh brackish lake environment with a relatively low sedimentation rate for this starved lake basin the bloom and death of algae in nutrient rich surface water supplied a large amount of organic matter to the lacustrine sediments the oxygen depleted bottom waters of the palaeo lakes favored the accumulation and preservation of sedimentary organic matter resulting in the formation of the organic rich shale a high quality source rock future exploration or assessment of the petroleum potential of the basin could be assisted by considering the proposed formation model of the organic rich shales and their distribution relative to potential traps

paleomagnetic investigation of upper permian sediments in the south junggar basin china lacustrine organic rich mudstones of the upper permian lucaogou formation are a significant petroleum source bed throughout most of the junggar basin in northwest china and paleomagnetic data may provide insight into tectonic conditions prevalent during their deposition secondary magnetizations were removed from 180 samples from 29 sites within the south junggar basin characteristic magnetizations of these samples were either revealed directly during thermal demagnetization or were calculated from great circle trajectories the primary nature of the characteristic magnetization is attested to by a positive fold test by exclusively reversed magnetizations which are consistent with the mid carboniferous to late permian kiaman reversed interval for the geomagnetic field and by relatively low levels of thermal maturity found in the mudstones tectonically corrected remagnetization circles and direct observations combined give a steep direction i 61 9 d 163 0 k 17 n 78 specimens the steep mean inclination recorded within the lacustrine organic rich mudstones suggests that junggar was situated near its present day latitude during deposition of the mudstones in late permian times consistent with the marginal ocean basin origin for junggar that has been proposed based upon stratigraphic relationships our data suggest that junggar may always have been associated with the northern continents of laurasia initially as a pre permian marginal ocean basin north of the tethys and subsequently as a permian mesozoic and cenozoic nonmarine foreland basin

molecular carbon isotope variations in core samples taken at the permian triassic boundary layers in southern china stable carbon isotope composition 13c of carbonate sediments and the molecular biomarker characteristics of a continuous permian triassic pt layer in southern china were studied to obtain geochemical signals of global change at the permian triassic boundary ptb carbonate carbon isotope values shifted toward positive before the end of the permian period and then shifted negative above the ptb into the triassic period molecular carbon isotope values of biomarkers followed the same trend at and below the ptb and remained negative in the triassic layer these biomarkers were acyclic isoprenoids ranging from c15 to c40 steranes c27 dominates and terpenoids that were all significantly more abundant in samples from the permian layer than those from the triassic layer the triassic layer was distinguished by the dominance of higher molecular weight waxy n alkanes stable carbon isotope values of individual components including n alkanes and acyclic isoprenoids such as phytane isop c25 and squalane are depleted in 13c by up to 8 10 in the triassic samples as compared to the permian measured molecular and isotopic variations of organic matter in the pt layers support the generally accepted view of permian oceanic stagnation followed by a massive upwelling of toxic deep waters at the ptb a series of large scale global outgassing events may be associated with the carbon isotope shift we measured this is also consistent with the lithological evidence we observed of white thin clay layers in this region our findings in context with a generally accepted stagnant permian ocean followed by massive upwelling of toxic deep waters might be the major causes of the largest global mass extinction event that occurred at the permian triassic boundary

sedimentology and magnetostratigraphy of the tierekesazi cenozoic section in the foreland region of south west tian shan in western china abstract the geology of tian shan provides an excellent example for understanding the intracontinental orogeny in the context of indian eurasian convergence previous studies leave much space in basinfill deposition process to be assessed in the regions west to the talas fergana fault tff we improve the understanding by conducting new investigations on sedimentology and magnetostratigraphy in the tierekesazi section of the foreland region of south west tian shan four lithofacies have been identified i marine lithofacies from the aertashi to bashibulake formations ii lacustrine to fluvial plain lithofacies from the keziluoyi to the middle pakabulake formations iii alluvial sand gravel sheet lithofacies in the upper pakabulake formation and iv conglomerate lithofacies from the atushi to xiyu formations magnetostratigraphic analysis accompanied with biostratigraphic correlation indicates that four lithofacies cover age intervals of ca 65 ma to 34 ma ca 22 1 ma to 12 ma 12 ma to 5 2 ma and 5 2 ma to approximately present with the sediment accumulation rates increasing from ca 2 4 3 3 3 5 compacted decompacted cm ka in the lithofacies i to 12 3 16 17 cm ka in the lithofacies ii to 16 3 19 5 20 6 cm ka in the lithofacies iii and finally to 22 8 22 8 cm ka in the lithofacies iv these results suggest three episodes of sedimentary events combined with previous results these episodes of sedimentary events are attributed to tectonic activities that are widespread along south tian shan we speculate that the oligo miocene boundary event more directly and likely marks the initial underthrusting of the tarim block beneath the south tian shan the mid miocene and mio pliocene boundary events although approximately synchronous between the regions east and west to the tff have different structural expressions in the two regions such difference is proposed to cause the dextral slipping of the tff and more fundamentally likely be driven by the northward indentation of the pamir at this time

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

the occurrence of isorenieratane and 24 n propylcholestanes in paleogene lacustrine source rocks from the dongying depression bohai bay basin implications for bacterial sulfate reduction photic zone euxinia and seawater incursions abstract lacustrine organic rich source rocks shales and mudstones were examined to assess the depositional environment and organic input sources of the third and fourth members of the eocene shahejie formation bohai bay basin china major organic contributions to the shahejie formation from dinoflagellates diatoms botryococcus and marine pelagophyte chrysophyte algae were determined using n alkane distributions gammacerane index and diagnostic steranes traces of higher plant biomarkers suggest that terrigenous organic inputs were limited the pervasive presence of carotane aryl isoprenoids paleorenieratane renieratane isorenieratane 2 methylhopanes and crocetane indicate significant organic contributions from bacterial communities including cyanobacteria purple sulfur bacteria chromatiaceae green sulfur bacteria chlorobiaceae and sulfate reducing bacteria the extent of h2s content bacterial sulfate reduction and photic zone euxinia pze were evaluated by determining the aryl isoprenoids ratio air 0 7 9 0 the presence of isorenieratene derivatives and the fate of sulfur in the water column there was a decrease of pze extent and duration from the northeast to the southwest of the palaeo lake and there was a decrease of water body salinity and bottom water anoxia from the fourth to the third member of the shahejie formation abrupt environmental perturbations in the third member of the shahejie formation are indicated not only by significant changes in parameters such as the pristane phytane and carotane n c20 alkane ratios the gammacerane index the isorenieratane c18 aryl isoprenoid and the air but also by the time lag in the expansion of cyanobacterial lineages after the expansion of purple green sulfur bacteria as well as seawater incursions the unexpected occurrence of intact c30 4 desmethylsteranes 24 n propylcholestanes in the shahejie formation is first reported here after very careful checking and provides unambiguous biological evidence for at least two marine transgression events reaching the eocene dongying palaeo lake the organic enrichment of the petroleum source rocks in the shahejie formation is a consequence of combined indigenous lacustrine algal production the constrained and favourable preservation conditions and significant bacterial contributions and marine organic matter inputs to the lake

molecular correlation of free oil and inclusion oil of reservoir rocks in the junggar basin china free oils and inclusion oils oil bearing fluid inclusions of 12 samples collected from the sandstone reservoir formations in the central eastern and northern areas of the junggar basin northwest china were analyzed by gc and gc ms analytical results indicate very similar biomarker distributions within each of the free oils and their associated inclusion oils in the two samples collected respectively from the northwestern and eastern border of the junggar basin the free oil and inclusion oil of sample md1 1 collected from the northwestern border correlate well with the permian source rock of the fencheng formation while those of sample dn1 1 from the eastern border correlate with the permian source rock of the pingdiquan formation in contrast in the central area the free and inclusion oils vary significantly in most cases which suggests variations of sources for oil charges during the filling process these data and the correlation between the free and inclusion oils are consistent with the field and seismic data which show that in areas where samples md1 1 and dn1 1 are located only one available source rock exists while in the central area multiple source rocks are present

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

petroleum migration and mixing in the potiguar basin brazil regional studies of petroleum samples from both offshore and onshore reservoirs of the potiguar basin brazil reveal compositional differences with discernible landward trends attributable to oil mixing these chemical discrepancies can be related to a combination of source rocks maturity and migration history the source rocks are classified in two groups based on their geochemical and molecular characteristics 1 neocomian and aptian lacustrine freshwater shales and 2 aptian marine evaporitic shales and marls both lie in an offshore structural low the geochemically contrasting oils derived from these source beds migrated updip constrained by a monoclinal structure through aptian carrier beds to thermally immature strata evaluation of compositional heterog neities in the oils and an investigation of migration effects on their compositions reveal trends related to the amount of mixing which in turn reflects the timing of both oil generation and migration and the direction of migration the more migrated oils contain greater contributions from freshwater sources whereas the less migrated oils display more pronounced contributions from the younger and shallower hypersaline source beds biomarker maturity parameters indicate that the most migrated oils are less mature consistent with their early generation from the deeper lacustrine freshwater source beds and migration to fill the shallower reservoirs first the results suggest that drainage of the basin evolved from lateral to vertical and enable prediction of the distribution of petrol um types within the basin

hydrocarbon evaporative loss evaluation of lacustrine shale oil based on mass balance method permian lucaogou formation in jimusaer depression junggar basin abstract hydrocarbon evaporative loss evaluation is important for shale oil resource assessment we propose a mass balance model to evaluate the hydrocarbon evaporative loss s1 loss in this study the proposed method is applied to a large rock eval pyrolysis dataset on source rock samples from the lucaogou formation in the jimusaer depression of the junggar basin nw china as a case study to evaluate the s1 loss the results indicate that the s1 loss can range from 0 12 to 7 25 mg g rock corresponding to 11 89 loss of the generated hydrocarbons s1 loss s1 s1 loss due to evaporation before lab analysis it appears that when ro 1 3 s1 loss and s1 loss toc decreases gradually with increasing ro likely corresponding to increasing oil density as results of heterogeneous source rock compositions and increased accommodation space via the creation of organic pores of large specific surface for heavy and large hydrocarbon molecules in oil window when ro 1 3 s1 loss toc begins to increase with increasing ro as more oil crack to gaseous and light hydrocarbons that are more susceptible to evaporative loss in the case of similar ro the relative s1 loss toc varies little among the samples but the absolute s1 loss amount increases with increasing toc restricted by regional geological conditions in this study we focused on the s1 loss for lacustrine type i kerogen only and quantification of evaporative loss for other kerogen types remains a subject for further study

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

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

organic petrology and geochemistry of mudrocks from the lacustrine lucaogou formation santanghu basin northwest china application to lake basin evolution abstract exploration for tight oil in the frontier santanghu basin of northwest china has resulted in recent commercial discoveries sourced from the lacustrine upper permian lucaogou formation already considered a world class source rock in the junggar basin to the west here we apply an integrated analytical program to carbonate dominated mudrocks from the lucaogou formation in santanghu basin to document the nature of organic matter om in the context of an evolving lake system the organic rich samples toc 2 8 11 4 wt n 10 were widely spaced from an 200 m cored section interpreted from textural and mineralogical evidence to document transition from a lower under filled to an overlying balanced filled lake organic matter is dominated by moderate to strongly fluorescent amorphous material with type i geochemical signature hi values 510 755 n 10 occurring in a continuum from lamellar stringers 10 20 m thick some 1 mm in length possible microbial mat preserved only in lower under filled section to finely disseminated amorphous groundmass intimately intermixed with mineral matrix biomarkers for methanotrophs and photosynthetic cyanobacteria indicate a complex microbial consortium a unicellular prasinophyte green alga similar to tasmanites in marine rocks is present as discrete flattened discs 50 100 m in diameter type iii om including vitrinite some fluorescent and inertinite also is abundant solid bitumen indicating local kerogen conversion fills voids and occurs throughout the cored section vitrinite reflectance values are 0 47 0 58 consistent with strong om fluorescence but may be suppressed other proxies e g biomarker parameters indicate the lucaogou formation is in the early oil window at this location on average slightly more amorphous om and telalginite are present in the lower section consistent with a shallow stratified saline environment with low sediment dilution more inertinite is present in the upper section indicating greater terrestrial influx and consistent with higher quartz and plagioclase content dominantly authigenic chalcedony and albite laminated mudstones in the upper section indicate anoxia prevented bioturbation from benthic grazing also indicating stratified water column conditions a decrease upsection in authigenic dolomite with reciprocal increase of ankerite siderite is consistent with decreasing salinity as is an overall decrease in gammacerane index values these observations suggest evolution from a shallow stratified evaporative saline setting to a deeper stratified freshwater basin with higher water input during lucaogou deposition the evolution from an under filled to balance filled lake in santanghu basin is similar to lucaogou deposition in junggar basin suggesting similar tectonic and climatic controls paleoclimate interpretations from other researchers in this area suggested an evolution from semi arid to humid conditions during the roadian we interpret that the evolution from an under filled to balanced filled lake seen in our data is in response to climate change and may represent increased groundwater delivery to the santanghu basin

tectonic and stratigraphic evolution of the mongolian people s republic and its influence on hydrocarbon geology and potential abstract the stratigraphy of mongolia can be divided into five megasequences each characterized by a common tectonic and stratigraphic history the earliest megasequence 1 precambrian silurian records the amalgamation of precambrian early palaeozoic passive and active margin terranes and the resulting growth of a caledonian fold belt in western mongolia megasequence 2 devonian permian appears to be the most complex with a variety of active margin collisions in southern and eastern mongolia and the continued deformation of the caledonian fold belt in the west a substantial fold belt underpinned by a variety of granitic plutons existed across mongolia by the triassic there was widespread erosion and limited deposition in small foreland and intermontane basins megasequence 3 triassic early jurassic megasequence 4 mid jurassic cretaceous records extension across the partially eroded fold belt with deposition confined to a series of alluvial and lacustrine rift basins these basins later experienced transpression inversion and erosion followed by onlap and overstep giving more widespread sedimentation from large post rift alluvial systems during the late cretaceous and tertiary megasequence 5 megasequences 1 3 are usually extensively folded megasequences 4 and 5 have been involved in transpressive inversion and mongolia is an area of present day compressive and transpressive tectonics erosion and general uplift the late jurassic early cretaceous sequences megasequence 4 are the most prospective for finding extractable hydrocarbons oil has been successfully produced from megasequence 4 alluvial and lacustrine rift sequences with rich oil prone lacustrine mudrocks which can form both source and seal facies interbedded sandstones siltstones and mudstones form various combinations of reservoirs and seals a large number of hydrocarbon trap types are yet to be tested past drilling has been concentrated around surface seeps and on simple structures that can be mapped at the surface with usually only shallow tests