hydrocarbon generation migration alteration entrapment and mixing in the central and northern north sea abstract there is little doubt that sediments of upper jurassic to lowermost lower cretaceous age particularly those of the kimmeridge clay formation and its equivalents are the source of the vast bulk of the oil in the central and northern north sea this is true both of oil in conventional mesozoic plays and in tertiary clastic reservoirs the timing of oil generation and migration ranges from the late cretaceous through to the present the oil productivity of the kimmeridge clay formation in the central graben moray firth and south viking graben areas of the north sea is estimated to be in excess of 250 billion barrels of which about 25 is accounted for in accumulations discovered to date there is strong areal differentiation between oil trapped in mesozoic reservoirs as opposed to upper cretaceous chalk and tertiary reservoirs this paper is particularly concerned with hydrocarbons in tertiary reservoirs which have a wide range of compositions and appear to have complex accumulation and degradation histories migration to chalk and younger tertiary reservoirs occurs often through thick shale sequences the evidence for the timing and mechanism of this process is considered and a preferred model for the vertical migration and subsequent lateral migration mixing and degradation is proposed

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

the occurrence of norlupanes and bisnorlupanes in oils of tertiary deltaic basins lupanoid hydrocarbons are known to occur in several petroleum systems and lupane c30 has recently been confirmed to exist in several crude oils in contrast norlupanes c29 and bisnorlupanes c28 are rarely observed in oil all of these compounds are considered to derive from natural products of angiosperms and numerous examples of their functionalized analogs are known the occurrence of c28 and c29 lupanoids in biochemical and geochemical systems is reviewed here and the presence and origin of their hydrocarbon analogs in crude oils are examined in detail although direct biochemical precursors for the lupane of crude oil are evident such precursors for norlupane and bisnorlupane are not obvious nor is it clear if the c28 and c29 analogs are diagenetic descendants from the lupane structure adding additional confusion is the occurrence of these analogs in oils which show numerous indications of post source molecular addition during migration and entrapment making it unclear if they originate from a conventional source rock or from carrier or seal rock despite these uncertainties there is extensive potential some of which has already been realized to use these compounds in oil oil and oil source rock correlations particularly in instances where extensive biodegradation has occurred deconvolution of the time s of introduction of norlupane and bisnorlupane into the fluid as well as various other hydrocarbons including olefins also provides great potential as a tool for mapping the migration history of an oil

dynamic topography produced by lower crustal flow against rheological strength heterogeneities bordering the tibetan plateau summary dynamic stresses developed in the deep crust as a consequence of flow of weak lower crust may explain anomalously high topography and extensional structures localized along orogenic plateau margins with lubrication equations commonly used to describe viscous flow in a thin gap geometry we model dynamic stresses associated with the obstruction of lower crustal channel flow due to rheological heterogeneity dynamic stresses depend on the mean velocity u viscosity and channel thickness h uniquely through the term u h 2 these stresses are then applied to the base of an elastic upper crust and the deflection of the elastic layer is computed to yield the predicted dynamic topography we compare model calculations with observed topography of the eastern tibetan plateau margin where we interpret channel flow of the deep crust to be inhibited by the rigid sichuan basin model results suggest that as much 1500 m of dynamic topography across a region of several tens to a hundred kilometres wide may be produced for lower crustal material with a viscosity of 2 10 18 p asfl owing in a 15 km thick channel around a rigid cylindrical block at an average rate of 80 mm yr 1

crustal deformation of the eastern tibetan plateau revealed by magnetotelluric imaging the ongoing collision of the indian and asian continents has created the himalaya and tibetan plateau through a range of deformation processes these include crustal thickening detachment of the lower lithosphere from the plate delamination and flow in a weakened lower crust 1 6 debate continues as to which of these processes are most significant 7 in eastern tibet large scale motion of the surface occurs but the nature of deformation at depth remains unresolved a large scale crustal flow channel has been proposed as an explanation for regional uplift in eastern tibet 6 8 9 but existing geophysical data 10 11 do not constrain the pattern of flow magnetotellurics uses naturally occurring electromagnetic waves to image the earth s subsurface here we present magnetotelluric data that image two major zones or channels of high electrical conductivity at a depth of 20 40 km the channels extend horizontally more than 800 km from the tibetan plateau into southwest china the electrical properties of the channels imply an elevated fluid content consistent with a weak crust 12 13 that permits flow on a geological timescale these findings support the hypothesis that crustal flow can occur in orogenic belts and contribute to uplift of plateaux our results reveal the previously unknown complexities of these patterns of crustal flow many previous studies of the indiaasia

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

the coupling of indian subduction and asian continental tectonics abstract in order to understand the potential controls on asian tectonics during the subduction of the tethys and indian lithospheres we reconstruct the coupled subduction continent deformation history using tomographic imaging kinematics constraints and numerical modeling the global p waves tomographic images of the mantle below the india asia collision zone provide constraints on the deep structure of continents and subduction history linking the slab positions in the mantle to the asian tectonics reconstructions and the indian plate kinematics we reconstruct the timing and location of successive subduction and breakoff events showing one major breakoff occurred between india and the tethys ocean 45 ma in the western syntax a vertical slab continuous to the continent is shown to override the deeper detached tethys slab in the central region similar structure is found with a detached slab yet closer to the tethys slab in the eastern syntax no slab is imaged it is inferred that after tethys slab had broke off subduction only resumed in the center of the margin while underthrusting took place at both extremities of the convergent margin during following convergence a second breakoff event detached the central indian slab from the margin 15 ma ago which renewed indian lithosphere underthrusting below asia this most probably occurred when the tibetan plateau was already uplifted implying that uplift is not a direct result of underthrusting numerical models of breakoff during subduction illustrate the controls of slab detachment on the complexities of the indian margin in these models the subduction of continental lithosphere resumes after breakoff only where this is entrained by the mantle flow associated with the long lasting oceanic slab sinking that is in the center of the margin while converging continent edges underthrusts the upper plate furthermore the breakoff during subduction has profound implications on the asian intra plate tectonics in the models the breakoff is rapidly followed by large stresses in the upper plate interiors propagating at large distance from the margin along a belt oriented at 45 from the trench the long term evolution of the asian continental tectonics shows drastic changes in the fault pattern with successive strike slip faulting across the asian continent which are in agreement with the mechanisms illustrated by the models transient large coupling at the trench caused by the breakoff events during india asia convergence offers an explanation for episodic nucleation of lithospheric faults within the asian continent and their link to deep processes

plate interactions crustal deformation and magmatism along the eastern margins of the tibetan plateau abstract in order to investigate the deep structure and dynamics of the triangular colliding system of the eastern tibetan plateau tp as well as the yangtze platform and the qinling dabie fold belt a large number of p and s wave arrival times from both local and teleseismic earthquakes were used to generate high resolution tomographic images beneath the eastern margins of tp the results of this study show that the western margin of the minjiang fault is characterized by low velocity low v anomalies in sharp contrast to the high velocity high v anomalies that are derived from the eastern part this means that the minshan uplift zone is imaged as high v and acts as a barrier to the eastward escape crustal flow which leads to obvious segmentation of the longmenshan fault lmsf zone between velocity belts that are concatenated into the minjiang fault because high v anomalies are clearly imaged in this study to extended depths of ca 450 km we consider the yangtze platform containing the sichuan basin to comprise craton like lithosphere this study reveals the presence of a low v belt extending to a depth of ca 250 km between the sichuan basin and the ordos block which probably represents the migration pathway of upwelling asthenosphere materials from tibet at the same time low v zone with a downdip depth of ca 500 km accompanied by an approximately 400 km rectangular high v body is imaged under the tengchong volcano we interpret the high v body and the low v zone as evidence for the subducted indian plate and the volcanic magma source respectively the results of this study reveal a number of new features of structural heterogeneities relative to deep coupling between the tibet and the yangtze platform as well as the relationship between the sichuan basin and the ordos block and the original source of the tengchong volcano the results presented here enable us a better understanding of the plate interaction crustal deformation and magmatism of the tengchong volcano along the eastern margins of tp

hydrocarbon reserves of gachsaran oilfield sw iran geochemical characteristics and origin abstract biomarkers and carbon isotope data were used to depict geochemical properties and to delineate source of the crude oils from asmari and bangestan reservoirs of the giant gachsaran oilfield sw iran despite the distinct horizons of the reservoirs and severe petrophysical heterogeneity inside each reservoir all oil samples show an identical level of thermal maturity furthermore similar source related parameters reflect identical source rock for both reservoirs they indicate carbonate marl source deposited in a marine environment under anoxic suboxic conditions strong marine organic matter signatures of predominantly algal origin along with evidence of a terrigenous angiosperm plant contribution were detected geochemical evidence suggests that the gachsaran field asmari and bangestan oils being sourced from a mix of organic rich kazhdumi and pabdeh source rocks of albian and middle eocene early oligocene ages respectively carbon isotope composition and v ni ratio signatures indicate kazhdumi formation as the main source rock meanwhile significant presence of oleanane and less than unity values of c 29 c 30 hopanes ratio demonstrate a partial contribution of pabdeh formation this contradiction could be explained by two scenarios 1 incorporating very immature non expelled pabdeh oils into the mature kazhdumi oils during migration or 2 partial charge form low maturity pabdeh oils that is insufficient to impact a typical mixed signature over the geochemical fingerprint of the reservoired oils additionally geochemical similarities give rise to an assumption of reservoir and trap inter connection for this giant field

early generation of 20s 5α h 14α h 17α h and 5α h 14β h 17β h steranes in low salinity lacustrine shales abstract a quantitative sterane biomarker study was conducted on a series of paralic freshwater lacustrine shale samples ranging in maturity from immature to near oil window maturity taken from section 3 of the shahejie formation es3 in the liaohe basin n e china concentrations of 5 h 14 h 17 h 20s and 5 h 14 h 17 h steranes remain nearly constant throughout the sample suite however the decrease in the absolute concentrations of the 20r 5 h 14 h 17 h c 29 steranes with increasing maturity results in an increase in the conventionally defined maturity parameters 20s 20 s 20r and sterane ratios in addition the data suggest that relatively early generation of 5 h 14 h 17 h 20s and 5 h 14 h 17 h steranes has occurred in lacustrine sediments with a vitrinate reflectance 0 3 r o the data provide strong support for the major importance of relative thermal stability of epimers but do not exclude the possibility of isomerization as a viable mechanism for production

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

structure of the crust beneath the southeastern tibetan plateau from teleseismic receiver functions abstract southeastern tibet marks the site of presumed clockwise rotation of the crust due to the india eurasian collision and abutment against the stable sichuan basin and south china block knowing the structure of the crust is a key to better understanding of crustal deformation and seismicity in this region here we analyze recordings of teleseismic earthquakes from 25 temporary broadband seismic stations and one permanent station using the receiver function method we find that the crustal thickness decreases gradually from the tibetan plateau proper to the sichuan basin and yangtze platform but that significant intra crustal heterogeneity exists on shorter lateral scales 0 30 are detected beneath the southeastern margin of tibet but in the sichuan basin and southeastern yangtze platform the values are close to the global average combined with high regional heat flow and independent evidence for mid crustal layers of high electric conductivity the large intra crustal s wave velocity reduction 12 19 and the intermediate to high average crustal poisson s ratios are consistent with partial melt in the crust beneath parts of southeastern tibet these results could be used in support of deformation models involving intra crustal flow with the caveat that significant lateral variation in location and strength of this flow may occur

crustal structure across longmenshan fault belt from passive source seismic profiling 1 we analyse receiver functions from 29 broad band seismographs along a 380 km profile across the longmenshan lms fault belt to determine crustal structure beneath the east tibetan margin and sichuan basin the moho deepens from about 50 km under songpan ganzi in east tibet to about 60 km beneath the lms and then shallows to about 35 km under the western sichuan basin the average crustal vp vs ratios vary in the range 1 75 1 88 under songpan ganzi in east tibet 1 8 2 0 under the lms and decrease systematically across the nw part of the sichuan basin to less than 1 70 a negative phase arrival above the moho under songpan ganzi and sichuan basin is interpreted as a ps conversion from the top of a low velocity layer in the lower crust the very high crustal vp vs ratio and negative polarity ps conversion at the top of lower crust in east tibet are inferred to be seismic signatures of a low viscosity channel in the eastern margin of the tibetan plateau the lateral variation of moho topography crustal vp vs ratio and negative polarity ps conversion at the top of the lower crust along the profile seem consistent with a model of lower crust flow or tectonic escape

seismic imaging crustal stress and gps data analyses implications for the generation of the 2008 wenchuan earthquake m7 9 china abstract seismic imaging together with global positioning system gps and crustal stress data analyses show that the mw7 9 2008 wenchuan earthquake occurred within a distinct area of high crustal stress 17 5 mpa and high poisson s ratio 7 10 anomalies centered on the longmen shan shan means mountain in chinese tectonic fault belt low p wave and s wave velocities in the southwest sw segment contrast with high velocity anomalies in the central portion cp and northeast ne segment within the uppermost 15 km depths along the tectonic fault belt though a presumably ductile zone with low velocity anomalies separates the cp and ne segment the rupture initiated near the southwestern end of the cp at a zone of high poisson s ratio which extends down into the lower crust these low velocity and high anomalies immediately below the source hypocenter together with the high crustal stress indicate the presence of high pressure fluids from the lower crust which might have reduced the mechanical strength of the fractured rock matrix and triggered the earthquake our study suggests that the structural heterogeneity and high crustal stress played an important role in the nucleation of the wenchuan earthquake and its rupture process

mode of cenozoic east west extension in tibet suggesting a common origin of rifts in asia during the indo asian collision cenozoic rifts in tibet were traditionally interpreted as a result of topographic collapse of the tibetan plateau reaching the maximum elevation that can be supported by its mechanical strength recent studies have emphasized possible similarities between rifting in tibet and extension in the basin and range of the western united states however when examined in detail one finds that spacing of long 100 km rifts in tibet 100 300 km is significantly greater than that in the basin and range 20 40 km from south to north rift spacing decreases systematically from 191 67 km in the himalaya south of the indus yalu suture to 146 34 km in south tibet between the indus yalu and bangong nujiang sutures and farther north to 101 31 km in central tibet between the bangong nujiang and jinsha sutures instability analysis suggests that the mantle lithosphere must have been involved in east west tibetan extension specifically the widely spaced rifts in the himalaya and tibet may have been related to the presence of a relatively light crust density 2 90 g cm 3 and a strong mantle lithosphere 40 km thick and a factor of 5 stronger than the upper crust the observed systematic decrease in rift spacing can be explained by the known decrease in the crustal thickness in tibet from 70 80 km in the himalaya in the south to 50 55 km in central tibet in the north a regional comparison of rifts in east asia suggests that both the involvement of the mantle lithosphere and the age of rift initiation are similar for tibetan rifts the baikal rift and the shanxi graben this implies that topographic collapse or a convective event in the mantle cannot be the sole cause for the development of the tibetan rifts a regional boundary condition applied throughout east asia must be required

structural heterogeneity of the longmenshan fault zone and the mechanism of the 2008 wenchuan earthquake ms 8 0 we determined detailed 3 d images of p and s wave velocity vp vs and poisson s ratio in and around the longmenshan lms fault zone by using a large number of p and s wave arrival times from the aftershocks of the 2008 wenchuan earthquake ms 8 0 and other local events our results show that the structure of the lms fault zone north of the wenchuan main shock is very different from that south of the main shock the southern section of the lms fault zone contains a broad zone with low vp low vs and high anomalies while the northern segment exhibits more scattered heterogeneities corresponding to most of the aftershocks which occurred there a prominent low vp low vs and high anomaly exists directly beneath the wenchuan main shock hypocenter suggesting that in addition to compositional variations fluid filled fractured rock matrices may exist in the lms fault zone which may have influenced the generation of the large wenchuan earthquake our tomographic results provide sound seismic evidence for the hypothesis that an upward intrusion of lower crustal flow occurred along the lms fault zone in addition most small earthquakes before the 2008 wenchuan main shock occurred around the guanxian jiangyou fault while the wenchuan aftershocks were mainly concentrated on the yingxiu beichuan fault suggesting that the rupture process of the wenchuan earthquake may belong to an out of sequence thrusting event a suggestion which is in good agreement with the results from geological surveys and also quite similar to the rupture processes of the 1999 chi chi earthquake m 7 5 and the 2005 kashmir earthquake m 7 6 a few aftershocks occurred close to the blind guangyuan dayi fault in the sichuan basin suggesting that this blind fault was also ruptured by the wenchuan earthquake consistent with geological surveys

new insights into the generation of the 2013 lushan earthquake ms 7 0 china global seismic waveform inversion can provide information on where the 2013 ms 7 0 lushan earthquake occurred in sichuan province china and how its aftershock sequence expanded to investigate the generation mechanism of the lushan earthquake and its relation to the 2008 wenchuan earthquake ms 8 0 50 temporary seismic stations were installed in the source area following the lushan earthquake crustal stress data were also collected along the longmen shan fault zone lmfz to reveal its influence on the generation of the lushan earthquake seismic imaging and crustal stress analysis have revealed that the lushan earthquake occurred in a distinct area with high velocity vp vs low poisson s ratio and high crustal stress the high velocity zone at the lushan source may reflect precambrian metasedimentary or igneous rock in the seismogenic layer which enables the accumulation of high crustal stress to generate large earthquakes however a sharply contrasting gap zone with low velocity high anomalies is clearly imaged in the upper crust under the concatenated area between the lushan and wenchuan earthquakes seismic images indicate that the low velocity gap zone is associated with fluid bearing ductile flow from the lower crustal materials of tibet being pushed into a weakened segment of the lmfz this study suggests that the 2013 lushan earthquake may have been triggered by high crustal stress accumulation together with high coseismic stress further increased by the wenchuan earthquake in the metamafic seismogenic layer contrasting rheological variations in the crust and crustal stress changes along the lmfz control the rupture processes that generated the lushan and wenchuan earthquakes as well as the generation of new earthquakes in the future

teleseismic p wave tomography and mantle dynamics beneath eastern tibet we determined a new 3 d p wave velocity model of the upper mantle beneath eastern tibet using 112 613 high quality arrival time data collected from teleseismic seismograms recorded by a new portable seismic array in yunnan and permanent networks in southwestern china our results provide new insights into the mantle structure and dynamics of eastern tibet high velocity high v anomalies are revealed down to 200 km depth under the sichuan basin and the ordos and alashan blocks low velocity low v anomalies are imaged in the upper mantle under the kunlun qilian and qinling fold zones and the songpan ganzi qiangtang lhasa and chuan dian diamond blocks suggesting that eastward moving low v materials are extruded to eastern china after the obstruction by the sichuan basin and the ordos and alashan blocks furthermore the extent and thickness of these low v anomalies are correlated with the surface topography suggesting that the uplift of eastern tibet could be partially related to these low v materials having a higher temperature and strong positive buoyancy in the mantle transition zone mtz broad high v anomalies are visible from the burma arc northward to the kunlun fault and eastward to the xiaojiang fault and they are connected upward with the wadati benioff seismic zone these results suggest that the subducted indian slab has traveled horizontally for a long distance after it descended into the mtz and return corner flow and deep slab dehydration have contributed to forming the low v anomalies in the big mantle wedge our results shed new light on the dynamics of the eastern tibetan plateau

crustal structure variation along 30 n in the eastern tibetan plateau and its tectonic implications abstract we determined crustal structure along the latitude 30 n through the eastern tibetan plateau using a teleseismic receiver function analysis the data came mostly from seismic stations deployed in eastern tibet and western sichuan region from 2004 to 2006 crustal thickness and vp vs ratio at each station were estimated by the h k stacking method on the profile the mean crustal thickness and vp vs ratio were found to be 62 3 km and 1 74 in the lhasa block 71 2 km and 1 79 near the bangong nujiang suture 66 3 km and 1 80 in the qiangtang block 59 8 km and 1 81 in the songpan garze block and 42 9 km and 1 76 in the yangtze block respectively the estimated crustal thicknesses are consistent with predictions based on the topography and the airy isostasy except near the bangong nujiang suture and in the qiangtang block where the crust is 5 10 km thicker than predicted indicating that the crust may be denser possibly due to mafic underplating we also inverted receiver functions for crustal velocity structure along the profile which reveals a low s wave velocity zone in the lower crust beneath the eastern tibetan plateau although the extent of the low velocity zone varies considerably the low velocity zone together with previous results suggests limited partial melting and localized crustal flow in the lower crust of the eastern tibetan plateau

geochemical comparison of three oil families from the gippsland basin se australia abstract the biomarker and aromatic compounds including polycyclic aromatic hydrocarbons pahs in three oil families composed of 29 crude oils from the gippsland basin se australia were studied using gas chromatography mass spectrometry environment related parameters such as the pr ph ratio and the gammacerane index indicate that all the oils originated from a lacustrine fluvial deltaic environment with fresh water thermal maturity related parameters including aliphatic and aromatic maturity indicators e g c29 sterane isomerisation parameters alkylnaphthalene indices and methylphenanthrene index show that all the oils from the ga1 oil family have a similar thermal maturity in the peak late oil window however oils from the ga2 and gb families vary in thermal maturity and are interpreted to be mixtures of less mature and more mature crude oils source related biomarkers e g isopimarane labdane and phyllocladane and pahs e g retene and oleanane ursane lupane derived aromatic triterpenoids suggest that the ga1 oils were mainly derived from source rocks rich in conifer derived organic matter the organic matter source of the ga2 and gb oil families included both angiosperms and gymnosperms with a relatively stronger angiosperm contribution to the organic matter in the source rock s of the gb oils based on the pah analysis moreover higher plant derived triterpenoids can be effectively used to correlate oil families across the study area supplementing the n alkane carbon isotope and biomarker data of the three oil families reported previously

biomarker evidence for two sources for solid bitumens in the subu wells implications for the petroleum prospectivity of the east papuan basin abstract late cretaceous sandstones from the subu 1 and 2 wells aure scarp papua new guinea contain patchily distributed solid bitumens the solid bitumens vary in reflectance and geochemistry indicating that they formed by the biodegradation of two different families of crude oils termed family a and family b biomarker characteristics such as the high abundance of rearranged hopanes and steranes indicate that the family a solid bitumens were derived originally from a clay rich marine source rock low in sulphur which had significant input of terrestrial organic matter these correlate with oils from the iagifu 7x gobe 3x omati 1 and puri 1 wells that are believed to be generated from sources of jurassic age the family b solid bitumens and a fluid inclusion oil from subu 1 have a high abundance of 2 methylhopanes bisnorhopanes and dibenzothiophene and originated from a marine source rock with a calcareous component this source rock had a high proportion of prokaryotic organic matter input a greater sulphur content and a more reducing depositional environment than the jurassic source rocks the lack of correlation with other oils in papua new guinea suggests the presence of a second so far unidentified generative marine source rock in the east papuan basin the fine grained samples in the subu wells are thermally immature vre 0 5 0 6 organically lean and contain type iii organic matter with little hydrocarbon generation potential most of the solid bitumens have peak oil window thermal maturities vre 0 8 1 0 but some have lowered maturities that are interpreted to be due to co extraction of indigenous detrital low maturity organic matter low molecular weight n alkanes alkylcyclohexanes methylalkylcyclohexanes and alkylbenzenes in many of the samples are attributed to overprinting of pre existing variably biodegraded solid bitumens in the sandstones with pristine hydrocarbon charge with a condensate composition this condensate charge has not undergone any major biodegradation or water washing implying that it is a relatively recent event solid bitumen from a vein in a miocene volcanolithic sandstone from the ouha anticline was generated from an early mature palaeogene or late cretaceous source rock that contained predominantly terrestrial organic matter deposited in an oxic environment this sample proves the existence of a different oil generative source rock in the east papuan basin in addition to the two oil source rocks inferred from the subu data

on the origin mixing and alteration of crude oils in the tarim basin abstract the origin of oil in the tarim basin northwestern china has been debated for decades here we present new insights into this challenging issue based on data from the bachu maigaiti area combined with a synthesis of data from other oil fields in the basin results of the organic geochemical characterization of 39 oil samples from various fields using gc fid py gc gc ms and gc ms ms revealed that the oils in the tarim basin can be generally classified into three families the oils of the first family whose representatives in our study come from the luntaibei condensate field are terrigenous as indicated by highest pristane phytane 2 8 and methylcyclohexane n heptane 1 8 and lowest dibenzothiophene phenanthrene 28 regular steranes and gammacerane a relatively high abundance of c 31 c 35 homohopanes as well as the presence of 1 2 3 4 tetramethylbenzene and aryl isoprenoids from c 13 to c 22 providing evidence for a contribution from green sulfur bacteria thriving under euxinic conditions the occurrence of these two marine oil families implies hitherto unknown organic facies for the respective source rocks family 2 oils may have been generated from cambrian shales deposited under suboxic conditions while family 3 oils could have been generated from cambrian to ordovician sources deposited in euxinic environments in addition biodegradation and mixing is quite common for the oils from the tarim basin mixing is evident not only by the coexistence of an unresolved complex mixture and c 7 c 36 n alkanes in certain oils but also by seemingly conflicting oil maturity parameters the results presented in this communication confirm the complexity of tarim basin petroleum systems in terms of ages and organofacies of the source rocks mixing of migrating and or accumulating petroleum and concomitant biodegradation

petroleum source maturity alteration and mixing in the southwestern barents sea new insights from geochemical and isotope data the hammerfest basin hb is an important area for petroleum exploration in the southwestern norwegian barents sea this contribution is aimed to characterize oils and condensates hosted in triassic and jurassic reservoirs establish genetic relationships and to assess maturity mixing and petroleum alteration processes the research was based on geochemical as well as bulk and compound specific stable carbon and hydrogen isotope analyses of oil and condensate samples from all major fields and discoveries in the hb including extracts from jurassic and triassic source rocks interpretations of light hydrocarbon composition and isotope data clearly identify four main petroleum groups affected by microbial degradation water washing evaporative fractionation and high thermal maturity level based on polycyclic aromatic hydrocarbons pahs marine and higher plant derived biomarkers and carbon isotopic composition 13c of individual petroleum hydrocarbons four petroleum families i iv are recognized in the hb and a distinction can be made among oils and condensates from different stratigraphic levels and sectors of the basin most oils and condensates from the hb consist of mixtures with small maturity variations however oils from middle triassic reservoirs in the goliat field showed larger maturity variations according to biomarker pah and light hydrocarbon maturity ratios in the hb geochemical and isotopic data allowed unraveling mixtures of hydrocarbons derived mainly from jurassic triassic and paleozoic source rocks

biodegradation of oil in uplifted basins prevented by deep burial sterilization biodegradation of crude oil by bacterial activity which has occurred in the majority of the earth s oil reserves is known to reduce greatly the quality of petroleum in reservoirs for economically successful prospecting for oil it is therefore important to understand the processes and conditions in geological formations that lead to oil biodegradation although recent studies speculate that bacterial activity can potentially occur up to temperatures as high as 150 degrees c refs 3 4 it is generally accepted that effective petroleum biodegradation over geological timescales generally occurs in reservoirs with temperatures below 80 degrees c ref 2 this appears however to be at odds with the observation that non degraded oils can still be found in reservoirs below this temperature here we compile data regarding the extent of oil biodegradation in several oil reservoirs and find that the extensive occurrence of non biodegraded oil in shallow cool basins is restricted to those that have been uplifted from deeper hotter regions of the earth we suggest that these petroleum reservoirs were sterilized by heating to a temperature around 80 90 degrees c during deep burial inactivating hydrocarbon degrading organisms that occur in the deep biosphere even when such reservoirs are subsequently uplifted to much cooler regions and filled with oil degradation does not occur implying that the sterilized sediments are not recolonized by hydrocarbon degrading bacteria

unraveling petroleum mixtures from the south viking graben north sea a study based on δ13c of individual hydrocarbons and molecular data abstract mixtures of compositionally different petroleum occur in the norwegian north sea one of the world s major oil producing regions the objective of the present contribution was to appraise the source maturity in reservoir mixing and alteration processes in a set of condensate and oil samples covering the main producing areas in the south viking graben svg furthermore this study focused on unraveling complex mixtures of petroleum and quantifying mixing ratios of hydrocarbons generated from jurassic source rocks the present research was based on a multiparameter approach that comprised the molecular composition of light hydrocarbons and heterocyclic and polycyclic aromatic compounds as well as the 13c of individual hydrocarbons in oils condensates and upper and middle jurassic source rock extracts from the svg according to the relative contribution of oils from type iii kerogen rich source rocks seven populations a g of mixed petroleum were identified by combining source related ratios of heterocyclic and non heterocyclic aromatic hydrocarbons and 13c values of n alkanes pristane pr and phytane ph the heterocyclic and polycyclic aromatic hydrocarbons provided a useful means to discriminate mixed hydrocarbons from source rocks of distinct organic matter type depositional environment and lithology in the svg the 13c enrichments of c10 c14 n alkanes and pr and ph were good indicators of the scale of the terrigenous source contribution and allowed quantitative determination of the proportions of jurassic source contributions enriched in type ii and type iii kerogens in complex petroleum mixtures from the southern part of the svg

mixing and biodegradation of hydrocarbons in the daerqi oilfield baiyinchagan depression northern china abstract crude oils in the daerqi oilfield vary greatly in viscosities including normal viscous and highly viscous oils they are also dramatically different in thermal maturity from immature to mature based on biomarker parameters according to bulk and molecular geochemical characteristics crude oils can be classified into three groups in this oilfield group i oils are mature and derived from the deeply buried and relatively old source rocks within the tengger formation and the second member of the arshan formation of early cretaceous age group ii oils are immature to marginally mature and derived from the relatively young source rocks that experienced shallow burial within the first member of the duhongmu formation of earlier cretaceous age group iii oils are mixtures of group i and group ii oils with dominance of the group i oils 70 the viscosity is low for the non biodegraded group i and group iii oils 7 1 24 mpa s but very high for the non biodegraded group ii oils e g 433 104 mpa s for the representative oil da12o1 the group iii oils are similar to the group i oils in gross properties e g gross composition and viscosity but are similar to group ii oils in terms of their molecular maturity parameters the oil reservoirs are currently at a shallow depth

neotectonics of the min shan china implications for mechanisms driving quaternary deformation along the eastern margin of the tibetan plateau the min shan region located along the eastern margin of the tibetan plateau north of the sichuan basin provides an important natural laboratory in which to study the rates and patterns of deformation and their relationship to mountain building at the margin of the plateau the topographic margin of the plateau is coincident with a north trending mountain range the min shan that stands nearly 2 km above the mean elevation of the plateau 3500 m in this region we exploit the preservation of a series of variably deformed quaternary sediments along the western flank of the range to investigate the pleistocene holocene deformation field within the min shan region mapping and field observations of remnant alluvial fans of late pleistocene age indicate that deformation within the min shan involved substantial 10 rapid down to the northwest tilting the geometry of the deposits and the partial preservation of an erosion surface beneath the basin suggest that much of the modern relief of the min shan relative to the tibetan plateau is a consequence of this late pleistocene tilting rates of tilting inferred from luminescence dating of interbedded loess have been remarkably rapid 10 8 rad yr similarly rapid rates of holocene differential rock uplift are inferred from tilted lacustrine sediments in the southwestern part of the range the range is bounded on the west by the min jiang fault zone an east vergent reverse fault however holocene alluvial terraces in headwaters of the min river are preserved across the fault in several places indicating that displacement rates on the min jiang fault are 1 mm yr active faulting only occurs along the eastern foot of the range huya fault for a short distance 60 km despite 3 km of relief on the eastern range front the relationship between these structures and the tilting observed in the min jiang basin is enigmatic the faults do not appear to exert a strong control on the rates and pattern of deformation within the basin a simple flexural model demonstrates that rates of tilting on the western flank of the min shan are too high to be simply attributed to an isostatic response to surficial loading and unloading of the lithosphere present day horizontal shortening across the min shan is geodetically determined to be less than 2 3 mm yr suggesting that only a small part of the observed tilting can be attributed to horizontal shortening thus tilting and concomitant differential rock uplift in the min shan appear to require an additional driving component we suggest that quaternary deformation along the western min shan may reflect the surface response to thickening of a weak lower crust at the margin of the tibetan plateau

deep structure and seismogenesis of the north south seismic zone in southwest china 1 to understand the deep structure and seismogenesis in the north south seismic zone nssz in southwest china we collected a large number of p and s wave arrival time data from both local earthquakes and teleseismic events to invert simultaneously for the three dimensional p and s wave velocity vp vs structures in the crust and upper mantle the obtained vp and vs models are generally coherent with each other from the crust to the mantle transition zone the nssz is characterized by strong structural heterogeneities from the mountainous areas of southeastern tibet to the yangtze platform low vp and low vs anomalies are generally imaged in the upper crust under the sichuan basin showing good agreement with the surface geological features that the foreland basin contains primarily mesozoic and paleozoic sedimentary rocks with a thickness of several kilometers the deep part of the yangtze platform is characterized by a cratonic lithospheric body dipping southwestward down to 400 km depth beneath the southeastern margin of the tibetan plateau in sharp contrast to low velocity anomalies in the upper mantle beneath the songpan ganzi fold system and the northwest qiangtang block at depths of the lower crust and uppermost mantle a layer with low vp and low vs 1 2 is revealed under a region west of the yangtze platform which may reflect the ductile flow in the lower crust our results indicate that the seismotectonics in the nssz is affected significantly by the ductile flow in the lower crust and strong heterogeneities in the upper mantle under southwest china in addition to the dominant role of the india asia collision

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

classification and thermal history of petroleum based on light hydrocarbons abstract classifications of oils and kerogens are described two indices are employed termed the heptane and isoheptane values based on analyses of gasoline range hydrocarbons the indices assess degree of paraffinicity and allow the definition of four types of oil normal mature supermature and biodegraded the values of these indices measured in sediment extracts are a function of maximum attained temperature and of kerogen type aliphatic and aromatic kerogens are definable only the extracts of sediments bearing aliphatic kerogens having a specific thermal history are identical to the normal oils which form the largest group 41 in the sample set this group was evidently generated at subsurface temperatures of the order of 138 149 c 280 300 f defined under specific conditions of burial history it is suggested that all other petroleums are transformation products of normal oils

first documentation of middle ordovician warm water carbonates in the mount jolmo lungma mount everest area southern xizang tibet china and its paleogeographic implications abstract a middle ordovician limestone succession representing part of the alai formation middle part of the chiatsun group of the himalayan orogenic belt is well exposed at jiacun section in nyalam county to the west of the mount jolmo lungma mount everest southern xizang tibet china the succession though reported previously has yet to be investigated in detail especially in the aspects of precise dating stratigraphic correlation and its paleogeographical affinities in this contribution we document for the first time the conodont biostratigraphy carbon isotope chemostratigraphy and microfacies analyses of this carbonate succession the conodont fauna indicates a middle darriwilian middle ordovician age corresponding to the histiodella holodentata biochronozone the carbon isotope records have shown minor fluctuations of 13c values with only a small negative carbon excursion in the lower part the microfacies analysis has resulted in the identification of seven microfacies including micritic limestone lithoclastic packstone non skeletal grainstone bioclastic limestone bioclastic lithoclastic limestone bioclastic lithoclastic oncoid limestone and bioclastic lithoclastic oncoid ooid limestone from thin sections fragments of crinoids brachiopods gastropods trilobites bryozoans and calcareous algae are identified abundant lithoclasts cortoids peloids oncoids and ooids together with the occurrences of dasyclad algae and hardgrounds are also recognized indicating a shallow and warm water marine environment and a likely tropical or subtropical affinity comparison of the lithofacies and faunas of this limestone succession of the alai formation with coeval strata in the zanskar spiti area northern india nepal bhutan canning basin west australia lhasa qiangtang sibumasu tarim and north china suggests that during the darriwilian these regions or terranes may have possessed a warm water marine environment and were located in low latitudinal zones it seems likely that this region of the northeastern gondwana and peri gondwana was protected from substantial influx of cool water currents derived from high latitudes at that time

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

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

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

receiver function analysis of crustal structure beneath the eastern tibetan plateau abstract we measure the crustal structure beneath the eastern tibetan plateau by analyzing three component teleseismic data recorded at 252 stations from january 1 2008 to march 31 2011 lateral variations of the crustal thickness and poisson s ratio are obtained by using receiver function method the thinnest crust is 27 km in the south yangtze craton and the deepest moho 70 km is estimated in the eastern margin of the tibetan plateau the distribution of poisson s ratio shows the heterogeneity that high poisson s ratios 0 27 are found in the chuandian plateau intermediate values 0 24 0 27 exhibit in the ordos block the qilian orogen the qinling dabie orogen the songpan ganzi terrane and the sichuan basin and low values 0 30 in the southeastern margin of the tibetan plateau can be considered as the evidence of the dominantly mafic composition or locally partial melting in crust our observations of the crustal thickness and poisson s ratio beneath the eastern tibetan plateau not only reveal the lateral inhomogeneity of the crustal structure but also provide some constraints on the mechanism of uplift and crustal thickening of the tibetan plateau

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

sulfur rich petroleum derived from lacustrine carbonate source rocks in bohai bay basin east china abstract crude oils produced from the zhanhua depression bohai bay basin are high in sulfur and differ from most lacustrine oils in this basin and elsewhere physical properties biomarker ratios and aromatic hydrocarbon assemblages reveal that they are derived from carbonate source rock horizons representative source rock samples with abundant organic matter toc 1 and s 2 5 mg hc g rock were selected for further correlation and their high bitumen contents indicated their indigenousness to saline or carbonate depositional environments the results of oil source rock correlation suggest that these sulfur rich heavy oils originate from es 3 4 carbonates and marls limited to the bonan sag maturity assessments with burial history showed that they were expelled at the early oil generation window high levels of 20s 5 14 17 and 5 14 17 steranes together with low values for the ts ts tm ratio and two methylated aromatic ratios mdr and mpi 1 were observed in these oils sulfur associated with evaporite and carbonate environments is a significant factor not only in controlling the occurrence of biomarker isomers but also for petroleum formation at abnormally low thermal stress levels

shear wave splitting in the southern margin of the ordos block north china 1 the southern margin of the ordos block in north china marks the transition from a stable cratonic block to active transextensional deformation in the weihe graben driven by the northeastward expansion of the tibet plateau we deployed 29 portable digital stations across this boundary and studied the upper mantle anisotropy using sks splitting the anisotropy is weak t 0 5 s at stations within the ordos block and in the north weihe graben but strong t 1 23 0 39 s in the south weihe graben and qinling orogen further south the directions of the fast s wave are 98 7 subparallel to the orientations of surface structures and the gps site velocities relative to stable asian continent we suggest that this e w oriented anisotropy is the result of both the collision between the north and south china blocks in the mesozoic and the eastward upper mantle flow driven by the indo asian collision

subduction of the indian lithosphere beneath the tibetan plateau and burma abstract subduction of the indian lithosphere under eurasia plays an important role in the tectonic evolution of the tibetan plateau and surrounding regions to improve our knowledge of pertinent mantle structures through tomographic imaging we combine p wave arrival time data from temporary arrays in tibet and stations of the chinese seismograph network with reprocessed data from the international seismological centre the new images reveal considerable spatial variations in mantle structure along the collision zone and the horizontal distance over which presumed continental indian lithosphere slides northward beneath the plateau decreases from west where it underlies the himalayas and the entire plateau to east where no indication is found for present day underthrusting beyond the himalayan block and indus tsangpo suture p wavespeed appears low in the shallow mantle beneath much of central and eastern tibet these observations suggest that indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of asian origin the continental parts of the indian plate that currently underthrust or subduct below the plateau appear generally detached from the oceanic slab fragments that subducted longer ago and that have been detected deeper in the mantle except perhaps in the central part of the collision zone 80 90 e this suggests that ongoing india eurasia collision must increasingly be driven by other forces such as subduction of the indian plate further west and east e g beneath indochina our images reveal structures associated with eastward subduction along the burmese arc southeast of the eastern himalayan syntaxis the tengchong volcanic complex in southwest china is marked by slow wave propagation to 150 km depth suggesting a causal link to subduction along the burmese arc the low velocities beneath the red river fault region extend to greater depth and may be related to upper mantle processes further southeast

crustal structure beneath the eastern margin of the tibetan plateau and its tectonic implications 1 two crustal cross sections through the eastern margin of the tibetan plateau are jointly determined from deep seismic sounding the e w trending line aa passes through the western sichuan plateau including the songpan garze terrane and the longmenshan fault belt and ends in the sichuan basin a part of the yangtze craton line bb has a trend of nne and crosses the songpan garze terrane two dimensional crustal structures along the profiles were jointly determined by the additional use of existing deep seismic sounding data our seismic velocity models indicate that the western sichuan plateau and the sichuan basin have crustal thicknesses of 62 and 43 km average crustal p wave velocities of 6 27 and 6 45 km s and lower crustal vp 6 5 km s thicknesses of 27 and 15 km respectively density models constructed from the seismic velocity models are consistent with observed bouguer gravity anomalies we infer that collision between the tibetan plateau and the yangtze craton has caused thickening of the lower crust and uplift of the western sichuan plateau we detect a low velocity layer in the upper crust of the western sichuan plateau but observe no equivalence in the sichuan basin west dipping thrusts may detach into this low velocity layer the seismic phase pmp in the western sichuan plateau has low amplitude suggesting high attenuation in the lower crust qp of 100 300 we suggest that the high attenuation is a consequence of lower crustal flow caused by the large lower crustal thickness beneath the western sichuan plateau

crustal structure in tengchong volcano geothermal area western yunnan china abstract based upon the deep seismic sounding profiles carried out in the tengchong volcano geothermal area tvga western yunnan province of china a 2 d crustal p velocity structure is obtained by use of finite difference inversion and forward travel time fitting method the crustal model shows that a low velocity anomaly zone exists in the upper crust which is related to geothermal activity two faults the longling ruili fault and tengchong fault on the profile extend from surface to the lower crust and the tengchong fault likely penetrates the moho moreover based on teleseismic receiver functions on a temporary seismic network s wave velocity structures beneath the geothermal field show low s wave velocity in the upper crust from results of geophysical survey the crust of tvga is characterized by low p wave and s wave velocities low resistivity high heat flow value and low q the upper mantle p wave velocity is also low this suggests presence of magma in the crust derived from the upper mantle the low velocity anomaly in upper crust may be related to the magma differentiation the tengchong volcanic area is located on the northeast edge of the indian eurasian plate collision zone away from the eastern boundary of the indian plate by about 450 km based on the results of this paper and related studies the tengchong volcanoes can be classified as plate boundary volcanoes

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

three dimensional velocity structure of crust and upper mantle in southwestern china and its tectonic implications using p and s arrival times from 4625 local and regional earthquakes recorded at 174 seismic stations and associated geophysical investigations this paper presents a three dimensional crustal and upper mantle velocity structure of southwestern china 21 34 n 97 105 e southwestern china lies in the transition zone between the uplifted tibetan plateau to the west and the yangtze continental platform to the east in the upper crust a positive velocity anomaly exists in the sichuan basin whereas a large scale negative velocity anomaly exists in the western sichuan plateau consistent with the upper crustal structure under the southern tibetan plateau the boundary between these two anomaly zones is the longmen shan fault the negative velocity anomalies at 50 km depth in the tengchong volcanic area and the panxi tectonic zone appear to be associated with temperature and composition variations in the upper mantle the red river fault is the boundary between the positive and negative velocity anomalies at 50 km depth the overall features of the crustal and the upper mantle structures in southwestern china are a low average velocity large crustal thickness variations the existence of a high conductivity layer in the crust or and upper mantle and a high heat flow value all these features are closely related to the collision between the indian and the asian plates

pn anisotropic tomography and dynamics under eastern tibetan plateau we present a new anisotropic tomographic model of the uppermost mantle around eastern tibet using pn traveltime data from a newly deployed temporary seismic array and recent observation bulletins of chinese provincial networks our results are generally consistent with previous results but provide new insights into the dynamics of tibetan plateau prominent high velocity high v anomalies are visible under alashan block and qaidam and sichuan basins which clearly outline their tectonic margins a distinct high v zone representing the double sided subduction of indo eurasian plates is imaged from lhasa block to the south of qaidam basin a pronounced low velocity low v zone is observed from songpan ganzi block to southern chuan dian diamond block suggesting the existence of hot material upwelling there crustal strong earthquakes frequently occurred around high v anomalies or transition zones from high v to low v anomalies suggesting that these earthquakes could be related to lateral heterogeneities in the mantle the pn fast direction approximately rotates around eastern himalayan syntaxis and it is tangential to the margins of sichuan basin suggesting that the mantle material flow of tibetan plateau may have affected east china in the yunnan region to the south of 26 n the pn fast direction is different from sks splitting results indicating that the mantle lithosphere could be mechanically decoupled at certain depth below the uppermost mantle which might be attributable to the subduction of indian or burma slab although the correlation between anisotropy and velocity is complicated anisotropy strength could be associated with the pattern of velocity anomalies in the region

cenozoic exhumation and deformation of northeastern tibet and the qinling is tibetan lower crustal flow diverging around the sichuan basin apatite fission track thermochronology data elucidate the cooling exhumation history of the qinling qin mountains which contain a paleozoic mesozoic orogenic collage north of the sichuan basin and northeast of the tibetan plateau in particular we examine the extent to which the qinling were affected by the rising plateau the northern and eastern qinling show continuous cooling and slow exhumation since the cretaceous in contrast in the southwestern qinling rapid cooling initiated at 9 4 ma a few million years later than in the eastern tibetan plateau a compilation of major cenozoic faults in the eastern tibetan plateau and the qinling and their kinematic and dynamic characterization shows that deformation in the qinling has predominantly been strike slip active sinistral and dextral strike slip faults delineate an area of eastward rock flow and bound the area of rapid late cenozoic cooling outlined by apatite fission track thermochronology these data can be interpreted to indicate that lower crustal flow has been diverted around the longmen shan and beneath the southwestern qinling causing active plateau uplift in this area alternatively northeastern tibet may be growing eastward faster in the western qinling than the entire south china block is extruding to the east

surface wave array tomography in se tibet from ambient seismic noise and two station analysis ii crustal and upper mantle structure summary we determine the 3 d shear wave speed variations in the crust and upper mantle in the southeastern borderland of the tibetan plateau sw china with data from 25 temporary broad band stations and one permanent station interstation rayleigh wave phase velocity dispersion curves were obtained at periods from 10 to 50 s from empirical green s function egf derived from ambient noise interferometry and from 20 to 150 s from traditional two station ts analysis here we use these measurements to construct phase velocity maps from 10 to 150 s using the average interstation dispersion from the egf and ts methods between 20 and 50 s and estimate from them with the neighbourhood algorithm the 3 d wave speed variations and their uncertainty the crust structure parametrized in three layers can be well resolved with a horizontal resolution about of 100 km or less because of the possible effect of mechanically weak layers on regional deformation of particular interest is the existence and geometry of low shear velocity layers lvls in some regions prominent lvls occur in the middle crust in others they may appear in the lower crust in some cases the lateral transition of shear wave speed coincides with major fault zones the spatial variation in strength and depth of crustal lvls suggests that the 3 d geometry of weak layers is complex and that unhindered crustal flow over large regions may not occur consideration of such complexity may be the key to a better understanding of relative block motion and patterns of seismicity

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

shear wave anisotropy beneath the tibetan plateau eleven broadband digital seismic stations were deployed across the central tibetan plateau in the first extensive passive source experiment attempted within the tibetan plateau one year of recording resulted in 186 event station pairs which we analyze to determine the characteristics of shear wave splitting in the upper mantle beneath the array measurements of the fast polarization direction and delay time t for sks and direct s arrivals reveal systematic variations along the north south oriented array in the north central region of the plateau very large delay times are observed at three stations the largest of which is budo with of t 2 4 s however at tunl which is off the northern edge of the plateau and 110 km from budo and at sites in the south central plateau t decreases by nearly a factor of 3 we also observe systematic rotation of from about 45 ne to 90 e w from south to north along the array a previously identified zone of inefficient sn propagation correlates well with our region of large t observations the large delay times suggest that a relateively high number of anisotropic crystals are preferentially alligned within the mantle lid beneath the north central portion of the tibetan plateau in most cases fast polarization directions appear to be parallel to surface geologic features suggesting as much as 200 km of the upper mantle has been involved in the collisional deformation that has produced the tibetan plateau

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

crustal shear wave velocity structure of northeastern tibet revealed by ambient seismic noise and receiver functions abstract the tibetan plateau is formed by the persistent convergence between the indian and eurasian plates the northeastern tibetan plateau is undergoing young deformation that has been noticed for a long time we conduct a passive source seismic profile with 22 stations in ne tibet in order to investigate the crustal shear wave velocity structure and its relationship with tectonic processes in this paper we obtain the rayleigh wave phase velocity dispersion data among all station pairs within the period bandwidth of 5 20 s from the method of ambient noise cross correlations phase velocity variations correlate well with surface geological boundaries and tectonic features for instance low phase velocity beneath the songpan ganzi block and the guide basin we also compute p wave receiver functions based on the selected teleseismic events with similar ray parameters and perform the joint inversion of surface wave dispersion data and receiver functions to obtain the 2 d crustal shear wave velocity structure along the profile the inversion results show that low shear wave velocities beneath the songpan ganzi block are widespread in the middle to lower crust in together with high crustal vp vs ratios and high temperature suggested by the p wave velocities obtained from the active source seismic study we suggest that the low velocity zone beneath the songpan ganzi block is probably attributed to partial melting across the north kunlun fault there is no crustal lvz found beneath the kunlun block this structural difference may have already existed before the collision of the two blocks or due to limit of the northward extension for the crustal lvz across the north kunlun fault

maturity related compositional changes in the low molecular weight hydrocarbon fraction of toarcian shales abstract compositional changes in the light hydrocarbon content of sedimentary rocks and petroleum are known to reflect their maturation history the present contribution comprises the study of the low molecular weight hydrocarbon fraction in core samples of lower toarcian age posidonia shale lias the samples series collected by shallow borehole drilling in the hils syncline lower saxony basin northern germany represents an excellent petroleum source rock type ii kerogen of a wide maturity range mean vitrinite reflectance rm between about 0 5 and 1 5 about 30 compounds in the c2 c7 molecular range were determined quantitatively using a combined thermovapourization capillary gas chromatography method both quantity and composition particularly of the c7 hydrocarbon fraction are discussed in relation to vitrinite reflectance values measured at five locations rm 0 48 0 66 0 68 0 88 and 1 45 correlations between rm and paraffin naphthene concentration ratios are described also the isomer concentration ratios of 2 methylhexane 3 methylhexane and of trans to cis 1 2 dimethylcyclopentane are clearly related to the maturity of the organic matter

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

crustal structure of the northeastern margin of the tibetan plateau from the songpan ganzi terrane to the ordos basin abstract the 1000 km long darlag lanzhou jingbian seismic refraction profile is located in the ne margin of the tibetan plateau this profile crosses the northern songpan ganzi terrane the qinling qilian fold system the haiyuan arcuate tectonic region and the stable ordos basin the p wave and s wave velocity structure and poisson s ratios reveal many significant characteristics in the profile the crustal thickness increases from northeast to southwest the average crustal thickness observed increases from 42 km in the ordos basin to 63 km in the songpan ganzi terrane the crust becomes obviously thicker south of the haiyuan fault and beneath the west qinlin shan the crustal velocities have significant variations along the profile the average p wave velocities for the crystalline crust vary between 6 3 and 6 4 km s beneath the songpan ganzi terrane west qinling shan and haiyuan arcuate tectonic region p wave velocities of 6 3 km s are 0 15 km s lower than the worldwide average of 6 45 km s north of the kunlun fault with exclusion of the haiyuan arcuate tectonic region the average p wave velocity is 6 4 km s and only 0 5 km s lower than the worldwide average a combination of the p wave velocity and poisson s ratio suggests that the crust is dominantly felsic in composition with an intermediate composition at the base a mafic lower crust is absent in the ne margin of the tibetan plateau from the songpan ganzi terrane to the ordos basin there are low velocity zones in the west qinling shan and the haiyuan arcuate tectonic region the low velocity zones have low s wave velocities and high poisson s ratios so it is possible these zones are due to partial melting the crust is divided into two layers the upper and the lower crust with crustal thickening mainly in the lower crust as the ne tibetan plateau is approached the results in the study show that the thickness of the lower crust increases from 22 to 38 km as the crustal thickness increases from 42 km in the ordos basin to 63 km in the songpan ganzi terrane south of the kunlun fault both the conrad discontinuity and moho in the west qinling shan and in the haiyuan arcuate tectonic region are laminated interfaces implying intense tectonic activity the arcuate faults and large earthquakes in the haiyuan arcuate tectonic region are the result of interaction between the tibetan plateau and the sino korean and gobi ala shan platforms

heterogeneity and anisotropy of the lithosphere of se tibet from surface wave array tomography 1 understanding the geotectonic evolution of the southeastern tibetan plateau requires knowledge about the structure of the lithosphere using data from 77 broadband stations in sw china we invert rayleigh wave phase velocity dispersion curves from ambient noise interferometry t 1 0 40 s and teleseismic surface waves t 2 0 150 s for 3 d heterogeneity and azimuthal anisotropy in the lithosphere to 150 km depth our surface wave array tomography reveals 1 deep crustal zones of anomalously low shear wave speed and 2 substantial variations with depth of the pattern of azimuthal anisotropy upper crustal azimuthal anisotropy reveals a curvilinear pattern around the eastern himalayan syntaxis with fast directions generally parallel to the main strike slip faults the mantle pattern of azimuthal anisotropy is different from that in the crust and varies from north to south the tomographically inferred 3 d variation in azimuthal anisotropy helps constrain the source region of shear wave splitting south of 26 n off the high plateau most of the observed splitting can be accounted for by upper mantle anisotropy but for stations on the plateau proper with thick crust crustal anisotropy cannot be ignored on long wavelengths the pattern of azimuthal anisotropy in the crust differs from that in the mantle this is easiest explained if deformation varies with depth the deep crustal zones of low shear wave speed and presumably mechanical strength may represent loci of ductile deformation but their lateral variation suggests that in se tibet localized crustal channel flow and motion along the major strike slip faults are both important

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

crustal structure of the paleozoic kunlun orogeny from an active source seismic profile between moba and guide in east tibet china abstract we herein present a new seismic refraction wide angle reflection profile that crosses the songpan ganzi terrane the animaqing suture zone and the eastern kunlun mountains comprised of the south kunlun and middle kunlun blocks separated by the middle kunlun fault the profile is 380 km long and extends from moba to guide in eastern tibet the crustal thickness is about 62 km under the songpan ganzi terrane 62 64 km under the south kunlun and 60 km under the middle kunlun block the songpan ganzi flysch seems to be present up to a depth of 15 km south of the animaqing suture zone and up to a depth of 10 km in the middle kunlun block with thicknesses elsewhere that depend on assumptions about the likely lithologies the profile exhibits clear lateral variations both in the upper and lower crust which are indicative of different crustal blocks juxtaposed by the kunlun fault system whether or not the songpan ganzi flysch was originally deposited on oceanic crust at the longitude of our profile 100 e it is now underlain by continental crust and the presence of continental crust beneath the songpan ganzi terrane and of a continental arc under the south kunlun block suggest paleozoic continent continent arc collision in the eastern kunlun mountains comparison of crustal velocity columns from all wide angle seismic profiles across the eastern kunlun mountains indicates a remarkable west to east change in the moho topography across the kunlun fault system 15 20 km moho step at 95 e but only 2 5 km along our profile at 100 e lower crustal thickness of the kunlun terranes is rather uniform about 35 km from 80 95 e which suggests that similar thrust thickening processes have played a role where the qaidam basin abuts the kunlun fault but thins to 20 25 km at 100 e east of the qaidam basin the increased crustal thickness from 93 to 98 e compared to that at 100 e may be due to the differences in the thickness of the crust of the two plates before their collision and or largely achieved by thickening of the lower crust perhaps indicating a crustal flow mechanism operating more strongly in the western region

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

complex indian subduction style with slab fragmentation beneath the eastern himalayan syntaxis revealed by teleseismic p wave tomography abstract on the eastern margin of the himalayan orogenic belt the rapid uplift of the namche barwa metamorphic terrane and significant bending of the yarlung zangbo suture zone occur the formation mechanism and dynamics of the eastern himalaya syntaxis ehs is still debated in order to better understand the deep structures beneath the ehs we deployed 35 broadband seismic stations around the namche barwa mountain the data were integrated with existing datasets for a 3 d teleseismic p wave tomography the results demonstrate complex deep structures and significantly contrasting indian subduction styles in the eastern himalaya in the western region of the ehs the indian slab flatly subducts under southern tibet and might extend to the bangong nujiang suture in contrast a north eastward steep subduction occurred in the eastern region of ehs the contrasting subduction styles result in tearing and fragmentation of the indian lithosphere between the flat and steep subducting slabs beneath the ehs consequently the hot asthenospheric mantle may rise through the slab window which might further lead to the rapid uplift of namche barwa and the formation of ehs the lateral variation in subduction collision mode and slab tearing induced asthenospheric mantle upwelling is similar to that observed in the hellenide and anatolide domains of the tethyan orogen

interstation pg and sg differential traveltime tomography in the northeastern margin of the tibetan plateau implications for spatial extent of crustal flow and segmentation of the longmenshan fault zone abstract interstation pg and sg differential traveltime tomography is performed in the northeastern margin of the tibetan plateau providing reliable mid lower crustal velocity images while minimizing errors from earthquake mislocation and origin time prominent low p and s velocities p and s in the northeastern tibetan plateau are bound to the east by the minjiang fault and the southwest segment of the longmenshan fault zone lmsfz in contrast relatively high p and s velocities 6 1 km s for v p and 3 7 km s for v s are found beneath the sichuan basin and in the triangular region bound to the west by the minjiang fault and to the east of the northeast segment of the lmsfz significant low velocity anomalies suggest a weak mid lower crust that flows beneath the eastern tibetan plateau while the high velocities beneath the sichuan basin indicate a rigid cold and stable crust the strong lithospheric mantle beneath the sichuan basin inferred from previous studies may act as a barrier to the eastward escape of crustal flow from the eastern tibetan plateau the segmentation of the lmsfz is reconfirmed by the distinct mid lower crustal velocities in the southwest and northeast segments high velocity and low conductivity anomalies in the mid lower crust beneath the eastern minshan uplift and the western qinling orogen suggest that no crustal flow reaches this area

oil oil and oil source rock correlations in the alpine foreland basin of austria insights from biomarker and stable carbon isotope studies abstract the alpine foreland basin is a minor oil and moderate gas province in central europe in the austrian part of the alpine foreland basin oil and minor thermal gas are thought to be predominantly sourced from lower oligocene horizons schoneck and eggerding formations the source rocks are immature where the oil fields are located and enter the oil window at ca 4 km depth beneath the alpine nappes indicating long distance lateral migration most important reservoirs are upper cretaceous and eocene basal sandstones stable carbon isotope and biomarker ratios of oils from different reservoirs indicate compositional trends in w e direction which reflect differences in source depositional environment facies and maturity of potential source rocks thermal maturity parameters from oils of different fields are only in the western part consistent with northward displacement of immature oils by subsequently generated oils in the eastern part of the basin different migration pathways must be assumed the trend in s s r isomerisation of c29 steranes versus the 20r 20r c29 steranes ratio from oil samples can be explained by differences in thermal maturation without involving long distance migration the results argue for hydrocarbon migration through highly permeable carrier beds or open faults rather than relatively short migration distances from the source the lateral distance of oil fields to the position of mature source rocks beneath the alpine nappes in the south suggests minimum migration distances between less than 20 km and more than 50 km biomarker compositions of the oils suggest oligocene shaly to marly successions i e schoeneck dynow and eggerding formations as potential source rocks taking into account their immature character best matches are obtained between the oils and units a b marly shale and c black shale of the normal schoneck formation as well as with the so called oberhofen facies results from open system pyrolysis gas chromatography of potential source rocks indicate slightly higher sulphur content of the resulting pyrolysate from unit b the enhanced dibenzothiophene phenanthrene ratios of oils from the western part of the basin would be consistent with a higher contribution of unit b to hydrocarbon expulsion in this area differences in the relative contribution of sedimentary units to oil generation are inherited from thickness variations of respective units in the overthrusted sediments the observed trend towards lighter 13c values of hydrocarbon fractions from oil fields in a w e direction are consistent with lower 13c values of organic matter in unit c

uppermost mantle structure of the eastern margin of the tibetan plateau from interstation pn traveltime difference tomography abstract tomographic inversion with interstation pn differential traveltime data provides a reliable velocity image of the uppermost mantle across the longmenshan fault belt which borders the eastern tibetan plateau and sichuan basin low pn velocities pn velocities 8 1 km s appear beneath the sichuan basin to the east suggesting a relatively weak upper mantle beneath eastern tibetan plateau and a strong upper mantle beneath the sichuan basin the pn velocities are consistent with the proposition that the rigid and stable lithosphere of the sichuan basin may act as a barrier to the eastward escape flow of the ductile crust of the eastern tibetan plateau consistency of pn velocities with the smoothed topography crustal thickness and bouguer gravity implies that the dynamic processes of the lithospheric mantle should be responsible for the crustal thickening and relief of uplift in the eastern tibetan plateau however the longmeshan fault belt appears to be separated into two segments by the huya and leidong faults as manifested by significant discrepancies in topography gradient seismic activity rupture process and aftershock distribution of wenchuan earthquake this segmentation is also supported by difference in pn velocities along the strike of the fault belt suggesting different tectonic environments in the crust and lithospheric mantle understanding of the mechanism for the segmentation requires further investigation

geochemistry of paleozoic marine oils from the tarim basin nw china part 4 paleobiodegradation and oil charge mixing abstract fifty three oil samples from paleozoic marine reservoirs of the tarim basin were analyzed by gc fid and gc ms to elucidate the influence of biodegradation and mixing on molecular compositions biodegradation has a major impact on many classes of compounds but the ultimate compositions and physical properties of the oil are influenced strongly by mixing with late oil charge subsequent to the process of biodegradation almost all samples display biodegradation signatures characterized by variable size of the unresolved complex mixture ucm and variable amounts of 25 norhopanes 25 nhs and 17 nortricyclic terpanes 17 nts the ubiquitous occurrence of n alkanes suggests that the petroleum accumulated in these fields is mainly a mixture of previously biodegraded oils with later migrated fresh oils the unaltered late charge of oil which has commingled with the initial biodegraded charge gives the wide range of oil gravities and asphaltene contents observed most commonly used maturity and depositional environment diagnostic parameters in the saturated hydrocarbon fraction are affected by biodegradation based on the intensity of 25 nhs and 17 nts oils from the tabei uplift appear to have experienced a much greater degree of biodegradation than those from the tazhong uplift however we caution against the simplistic use of molecular indicators to define a specific level of biodegradation in this case study as it may be somewhat misleading for physical property prediction a wide range of estimated maturity values from different components provides an important clue for multiple charge and mixing interpretations the relationship between the absolute concentrations of compound class and peak hump ratios of the samples can potentially qualitatively differentiate the pulse of inputs to the mixed oils the positive correlation between the concentrations of a given compound class and peak hump ratios may suggest that that class of compounds is most likely derived from the late charge after biodegradation while the negative correlation may indicate compounds largely inherited from the early charge before biodegradation some compounds show almost no correlation between their concentrations and peak hump ratios implying more similar intensity of charge inherited from early pulse and amalgamated from later pulses in some extremely biodegraded cases where ucm hump can also be diminished not in present case study the correlation between compound class concentrations and peak hump ratios will be more complicated

confined pyrolysis of tertiary lacustrine source rocks in the western qaidam basin northwest china implications for generative potential and oil maturity evaluation abstract the parameter s 1 s 2 genetic potential of rock eval analysis is widely used as an evaluation of the genetic potential for the source rocks oligocene miocene saline lacustrine source rocks in the western qaidam basin have low total organic c contents toc most around 0 5 with a few exceptions 1 0 mineral matrix effects are substantial for source rocks with low toc resulting in relatively low s 1 and s 2 peaks based on the results of confined pyrolyses sealed au capsules on 6 oligocene miocene source rocks from the western qaidam basin with toc ranging between 0 48 and 2 22 the relationship between the s 1 s 2 parameter and the maximum amount of extracted bitumen or saturated and aromatic hydrocarbons sa after the confined pyrolysis has been established as follows bitumen mg g rock 1 4924 s 1 s 2 0 3201 r 0 987 or sa saturates aromatics mg g rock 0 7083 s 1 s 2 0 4045 r 0 992 based on these formulas the amounts of hydrocarbons generated from source rocks can be reasonably estimated the typical crude oils with low biomarker maturities in this region appear substantially different to the pyrolysates of these six rocks at 180 300 c but comparable to the pyrolysates at 320 c and higher temperatures based on molecular parameters this result in combination with the physical and gross compositions of the crude oils suggests that the majority of these crude oils were generated from the source rocks during the main oil generative stage possibly at a maturity higher than r o 0 74

structural control of rupturing of the mw7 9 2008 wenchuan earthquake china abstract analyses of global seismic waveform data for the 2008 devastating wenchuan earthquake have indicated where the rupture started and how it expanded here we reveal that the rupture process of this earthquake was strongly controlled by structural heterogeneities of the upper crust we made a tomographic inversion of 200 000 local travel time data according to which the rupture was confined in a presumably brittle layer of high p and s wave velocity anomalies within the upper 15 km depths the rupture propagated northeastward through the southwest sw segment of the fault and then jumped to the northeast ne segment with little slip at the intervening presumably ductile zone characterized by low p and s velocities with high poisson s ratio the rupture initiated near the southwestern end of the sw segment within a body of high poisson s ratio which extends down into the lower crust suggesting upward migration of deep seated aqueous fluid to trigger the earthquake by reducing the mechanical strength of the brittle layer

amount of asian lithospheric mantle subducted during the india asia collision abstract body wave seismic tomography is a successful technique for mapping lithospheric material sinking into the mantle focusing on the india asia collision zone we postulate the existence of several asian continental slabs based on seismic global tomography we observe a lower mantle positive anomaly between 1100 and 900 km depths that we interpret as the signature of a past subduction process of asian lithosphere based on the anomaly position relative to positive anomalies related to indian continental slab we propose that this anomaly provides evidence for south dipping subduction of north tibet lithospheric mantle occurring along 3000 km parallel to the southern asian margin and beginning soon after the 45 ma break off that detached the tethys oceanic slab from the indian continent we estimate the maximum length of the slab related to the anomaly to be 400 km adding 200 km of presently asian subducting slab beneath central tibet the amount of asian lithospheric mantle absorbed by continental subduction during the collision is at most 600 km using global seismic tomography to resolve the geometry of asian continent at the onset of collision we estimate that the convergence absorbed by asia during the indentation process is 1300 km we conclude that asian continental subduction could accommodate at most 45 of the asian convergence the rest of the convergence could have been accommodated by a combination of extrusion and shallow subduction underthrusting processes continental subduction is therefore a major lithospheric process involved in intraplate tectonics of a supercontinent like eurasia

unravelling maturity and migration related carbazole and phenol distributions in central graben crude oils abstract in this contribution we present the results of an integrated investigation of selected nitrogen and oxygen bearing compounds in norwegian central graben crude oils we first provide an interpretation framework built on hydrocarbon biomarkers and then use this framework to relate polar compound geochemistry to the influences of source facies farsund versus mandal formations maturity migration and reservoir lithology oil maturity could be assessed using established changes in carbazole annelation n1 dbe 9 vs 12 vs 15 classes as well as hydrocarbon biomarkers 29ts 29ts nh correlated best with the polar compound maturity data secondary migration fractionation appears nevertheless to have played a role as seen by increased dbe 9 and 12 carbazole and benzocarbazole proportions and a loss of c2 3 dbe 12 homologues within carbonate reservoirs as compared to intraformational upper jurassic siliciclastic reservoirs thus migration distances pathways and wettability of carrier systems ostensibly play a significant role in carbazole distributions of the central graben oils manifesting itself as apparent maturity retardation in an attempt to eliminate the migration component from maturity assessment we here present a novel ternary diagram including dibenzocarbazoles n1 dbe 15 and phenolic species o1 dbe 4 and 5 based on a single measurement using the ft icr ms however the integration of such results into 3d modelling software must be conducted to clarify source kitchen migration pathways and distances

seismic anisotropy beneath tibet evidence for eastward extrusion of the tibetan lithosphere strong seismic anisotropy beneath tibet has recently been reported from the study of sks shear wave splitting the fast split waves are generally polarized in an easterly direction close to the present day direction of motion of the tibetan crust relative to stable eurasia as deduced from holocene slip rates on the major active faults in and around tibet this correlation may be taken to suggest that the whole tibetan lithosphere is being extruded in front of indenting india and that the anisotropic layer is the deforming asthenosphere that accommodates the motion of the tibetan lithosphere relative to the fixed mantle at depth uncertainties about this motion are at present too large to bring unambiguous support to that view assuming that this view is correct however a simple forward model is used to compute theoretical delay times as a function of the thickness of the anisotropic layer the observed delay times would require a 50 100 km thick anisotropic layer beneath south central tibet and an over 200 km thick layer beneath north central tibet where particularly hot asthenosphere has been inferred this study suggests that the asthenospheric anisotropy due to present absolute block motion might be dominant under actively deforming continents

insight into the origin of the tengchong intraplate volcano and seismotectonics in southwest china from local and teleseismic data received 18 june 2008 revised 22 february 2009 accepted 10 march 2009 published 13 may 2009 1 a high resolution tomographic image of the crust and upper mantle under yunnan province in southwest china was determined by using a large number of teleseismic data measured precisely from digital seismograms as well as local earthquake arrival times recorded by the dense yunnan seismic network the grid spacing of the tomographic model is 70 km 78 km in the horizontal directions and 4 70 km in depth our resulting model shows a clear low velocity low v 0 3 with respect to the average one dimensional velocity model column extending from the surface down to about 400 km depth under the active tengchong volcano and some high velocity high v anomalies existing in the mantle transition zone furthermore the low vanomaly extends horizontally toward the northeast at 250 to 400 km depth combining our tomographic results with geochemical and geological investigations we infer that the tengchong volcano is a rift related volcano caused by the subduction and dehydration of the indian plate as well as corner flow in the mantle wedge though the subducted slab is a continental plate our results show that the upwelling flow under tengchong originates at 400 km depth a prominent low v anomaly along the red river fault zone extends down to the upper mantle 100 km depth reflecting that the red river fault zone may have cut through the crust to the upper mantle the two dayao earthquakes m 6 1 and m 6 2 in 2003 occurred on the margin of high v anomalies and are underlain by a prominent low v anomaly in the lower crust and upper mantle suggesting that the dayao earthquakes may be associated with fluids released from the dehydration of the subducted indian slab these results are significantly improved compared with previous studies and provide new seismic constraints on the dynamic processes of the india asia collision

tomographic imaging of the underthrusting indian slab and mantle upwelling beneath central tibet abstract to better understand the pattern of convergence between the indian and eurasian plates we determine a high resolution p wave tomography of the crust and upper mantle under southern to central tibet using a large number of high quality data of local earthquakes and teleseismic events collected by the antilope ii and hi climb projects a significant low velocity zone is detected above the northward underthrusting indian slab beneath the indus tsangpo suture which may reflect fault zones or incomplete fragmentation as well as melts and or fluids associated with the dehydration of the underthrusting indian slab the variations in the diving depth and extending distance of the indian slab under the antilope ii and hi climb seismic profiles may be caused by the differences in the viscosity contrast between the indian slab and the surrounding mantle as well as strong structural heterogeneities in the upper mantle under the study region both high and low velocity anomalies are revealed in the mid to lower crust under southern tibet which may reflect the complex pattern of crustal structure the rifts in southern tibet exhibit different velocity images suggesting that different structures exist beneath those rifts

deep slip rates along the longmen shan fault zone estimated from repeating microearthquakes 1 we investigated deep slip rates along the longmen shan fault zone where the devastating 2008 m7 9 wenchuan earthquake occurred using repeating earthquake data recorded by two digital seismic networks near the fault using cross correlation analysis of waveform data we identified a total of 231 doublets and 224 multiplets that have highly similar waveforms most of these sequences are aperiodic with recurrence intervals varying from a few minutes to hundreds of days for each multiplet we first constructed a reference seismogram at each station and used it to measure the delay time of the p and s waves of each event within the cluster we used the delay times to determine the relative distances between each event and the cluster centroid the relative distances were used in screening repeating events in each multiplet we identified a total of 12 repeating earthquake clusters in the source region of the m7 9 wenchuan earthquake most of the clusters are located at the edge of locked areas where large coseismic slips were observed during the 2008 wenchuan earthquake suggesting a close spatial relationship between microearthquakes and impending large devastating earthquakes the measured in situ deep slip rates appeared to increase with depth and varied from 3 5 to 9 6 mm yr at depth range of 4 18 km they are approximately twice as large as those inferred from surface gps and geological data our results here have significant implications to the understanding of faulting as well as risk assessment of seismic hazards

cenozoic rifting and volcanism in eastern china a mantle dynamic link to the indo asian collision abstract the indo asian continental collision is known to have had a great impact on crustal deformation in south central asia but its effects on the sublithospheric mantle remain uncertain studies of seismic anisotropy and volcanism have suggested that the collision may have driven significant lateral mantle flow under the asian continent similar to the observed lateral extrusion of asian crustal blocks here we present supporting evidence from p wave travel time seismic tomography and numerical modeling the tomography shows continuous low velocity asthenospheric mantle structures extending from the tibetan plateau to eastern china consistent with the notion of a collision driven lateral mantle extrusion numerical simulations suggest that at the presence of a low viscosity asthenosphere continued mass injection under the indo asian collision zone over the past 50 my could have driven significant lateral extrusion of the asthenospheric mantle leading to diffuse asthenospheric upwelling rifting and widespread cenozoic volcanism in eastern china

bakken madison petroleum systems in the canadian williston basin part 3 geochemical evidence for significant bakken derived oils in madison group reservoirs there have been two different definitions of the upper devonian mississippian bakken madison petroleum systems in the canadian williston basin early studies proposed the bakken shales as the source for oils in both the bakken formation and madison group reservoirs more recent studies suggested two separate sources for these oils thus the bakken oils were interpreted to be derived from the bakken formation shales and the madison group oils from a carbonate source within the madison group the present study utilized quantitative results of molecular markers across gasoline range light hydrocarbons saturated and aromatic hydrocarbon fractions in 122 oil samples to re evaluate the oil oil and oil source relationships the steroid and hopanoid parameters collected in this study have confirmed the diagnostic features for end member bakken and lodgepole sources whereas a range of other molecular markers revealed compositional continuums occurring between the two oil families the recognition of more extensive mixing of bakken derived oils in madison group reservoirs along a sw ne trending fault fracture zone in southeastern saskatchewan indicates focused migration pathways for bakken oils and thus upward resource potentials the results also suggest caution with the use of conventional biomarker data in oil oil and oil source correlation when the different sources concerned contain biomarkers in drastically different concentrations

a low velocity belt beneath northern and eastern tibetan plateau from pn tomography 1 new pn tomography on tibetan plateau tp and neighboring region is conducted with data assembled from various sources the improved pn tomographic image delineates several distinct geophysical regimes that are approximately separated by geological boundaries at surface dense distribution of the stations in the eastern half of the plateau allows us to infer a 3d view of crustal thickness variation of the region the most striking feature is the bended low velocity belt lvb which extends from west to east beneath qiangtang block and songpan ganzi fold belt sgfb in northern tp and then turns consistently southward with sgfb beneath eastern tp and further south to indo china the consistency between geological boundaries on surface and sharp velocity contrast boundaries in uppermost mantle may suggest strong deformation coupling between crust and at least uppermost mantle if not whole lithosphere a north south striking lvb is also observed cutting through the southern tp coinciding with the yadong gulu rift at surface our tomographic results are generally consistent with dynamic models that involve with underthrusting in the southern tp shortening in the northern tp and extrusion to the east and the southeast furthermore our results suggest significant east west variations in the structure and dynamics