active deformation to the north of the altyn tagh fault constraints on the northward growth of the northern tibetan plateau abstract sinistral transpressive deformation occurs in the region north of the altyn tagh fault due to the indo eurasian collision in this region several late cenozoic faults have developed and the sanweishan fault is the key feature with clear landforms in this study slip rate measurements combined with several dating methods imply that the sanweishan fault has been active with sinistral strike slip rates of 0 33 0 04 mm a since 14 ka bp and 0 28 0 03 mm a since 20 ka bp which are more than an order of magnitude smaller than that of the atf to the south the horizontal displacements are 1 7 5 5 m in the eastern segment and 25 0 76 0 m in the middle and western segments of the sanweishan fault the increment of horizontal displacement along the main sanweishan fault is 3 0 4 0 m between paleoearthquakes and the magnitude of the latest paleoearthquake on the middle and eastern segments of the fault is up to m 7 2 7 5 the whole length of the sanweishan fault is 360 km or longer which include active faults in the yangguan and danghe reservoirs in the west more components of thrusting occur on the western and eastern segments of the sanweishan fault the growth of the sanweishan fault is similar to that of the atf but the former fault is younger and its slip rate is much smaller the differential slip rates on the sanweishan fault and atf may result in the clockwise rotation and eastward movement of the intervening block which compresses regions to the northeast

the white stone band of the kimmeridge clay formation an integrated high resolution approach to understanding environmental change the kimmeridge clay is a jurassic mudrock succession that shows milankovitch band climatic cyclicity a key issue is to determine how the subtle changes that define this cyclicity result from climatic change using material from the natural environment research council rapid global geological events rgge kimmeridge drilling project boreholes the white stone band was investigated at the lamination scale using backscattered electron imagery and quantitative palynofacies fabric analysis shows the lamination to represent successive deposition of coccolith rich and organic matter rich layers individual laminae contain unsorted palynological debris with a consistent ratio of marine and terrestrial components such mixed organic matter input is interpreted as the result of storm transport linking water column processes to laminae deposition suggests seasonal input with a coccolith bloom followed by a more diverse assemblage including dinoflagellates and photosynthetic chlorobiacean bacteria as the photic zone extended into the euxinic water column organic matter export to the sea bed underwent minimal cycling through oxidation and subsequently became preserved through sulphurization with greatly increased sequestration of carbon this was significantly increased by late season storm driven mixing of euxinic water into the photic zone increased frequency of storm systems would therefore dilute the coccolith input to give an oil shale hence climatically induced changes in storm frequency would progressively vary the organic content of the sediment and generate the climate cycle signal

magnitude of post middle jurassic bajocian displacement on the central altyn tagh fault system northwest china the altyn tagh fault system a key structural feature in the tectonic collage of central asia is an active left lateral strike slip fault system however its age of initiation kinematic history and total magnitude of displacement are not well known middle jurassic nonmarine sedimentary rocks that crop out along the central segment of the altyn tagh fault were deposited in a contiguous tarim qaidam foreland style basin that was geodynamically linked to mesozoic contraction in the tian shan bei shan qilian shan and kunlun shan this study documents the best evidence of a piercing point to date consisting of an offset lacustrine shoreline demarcated by aalenian bajocian open lacustrine strata to the west and fluvial and alluvial strata of comparable age to the east detrital compositions palynology paleocurrents and lithostratigraphy support correlation of these sections restoration of this jurassic facies boundary indicates 400 60 km of post bajocian left lateral separation on the altyn tagh fault consistent with this result restoration of the jurassic shoreline aligns felsic plutons across the western segment of the altyn tagh fault system that may have been left laterally offset by 360 km these two pairs of offset features suggest that the current best estimate for net magnitude of post bajocian left lateral separation on the altyn tagh fault is about 360 km

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

deep structures and surface boundaries among proto tethyan micro blocks constraints from seismic tomography and aeromagnetic anomalies in the central china orogen abstract the qinling qilian orogen preserves the records of early paleozoic convergence among the proto tethyan micro blocks in this study we analyze the seismic velocity structure and the aeromagnetic anomalies in the qinling qilian orogen and its adjacent areas showing that the northernmost boundaries of these proto tethyan micro blocks are defined by the guyuan longshoushan fault in the qilian orogen and by the luonan luanchuan fault in the qinling orogen respectively the lithosphere north of the qinling qilian orogen subducted southward under the qinling qilian orogen the boundaries of the micro blocks in the qinling qilian orogen of the proto tethys domain are mostly ew or ne trending combined with early paleozoic geological records our results indicate that the south dipping low velocity anomaly under the alxa block and the south dipping high velocity ones under the north qilian orogen and the north china block might indicate that the alxa block the north qilian oceanic slab and the north china block subducted southward the south dipping high velocity anomaly under the north qilian orogen is interpreted as the remnant of the proto tethys ocean in that area however the north dipping low velocity anomaly under the south qinling and the north qinling orogens the qaidam block and the north dipping high velocity one under the yangtze and the bikou blocks suggest that the south qinling and the north qinling orogens the qaidam the yangtze and the bikou blocks subducted northward the present spatial framework of the qinling qilian orogen is related to early paleozoic convergence among the proto tethyan micro blocks

is the north altyn fault part of a strike slip duplex along the altyn tagh fault system although the altyn tagh fault system has played an important role in the indo asian collision its geometry and tectonic evolution remain poorly known between 86 and 92 e this system is at least 100 km wide and is bounded to the north and south by the north altyn and altyn tagh faults respectively mapping along the jianglisai reach of the north altyn fault indicates that miocene to pliocene motion was predominantly left to left reverse slip with transport vectors trending n45 60 e map relationships suggest that total offset on the fault is 120 km these results are inconsistent with previous models of the altyn tagh fault system in which oblique convergence along the northern margin of the tibetan plateau is partitioned into thrusting on the north altyn fault and left slip on the altyn tagh fault an alternative hypothesis is that the north altyn fault is the northern boundary of a transpressional strike slip duplex within which the structurally elevated altyn mountains were created our model suggests that transpressional deformation may be restricted to this strike slip duplex and need not characterize the entire margin

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

photic zone euxinia in the central rhaetian sea prior the triassic jurassic boundary abstract shortly after the deposition of black shales in the rhaetian sea central european basin ceb the triassic jurassic tr j boundary witnessed one of the big five mass extinction events in earth s history aiming at a better understanding of paleoenvironmental changes in the geochemically less well known middle to late rhaetian german subdivision we studied samples from a cored borehole from the central rhaetian sea in nw germany hebelermeer 2 biomarkers palynomorphs and bulk geochemistry all support a marine brackish setting with inputs from terrestrial plants dinosteranes were found throughout the core most likely suggesting the spread of dinoflagellates it is widely accepted that volcanic exhalations during the development of the central atlantic magmatic province camp had a major impact on marine and terrestrial environments in the earliest jurassic e g the development of photic zone euxinia and h2s poisoning of benthic life there is evidence from the studied core however that comparable conditions already thrived in the central rhaetian sea during the middle rhaetian a first indication of euxinia anoxia is evident from low to very low total organic carbon versus total sulfur toc ts ratios

late cenozoic tectonic activity of the altyn tagh range constraints from sedimentary records from the western qaidam basin ne tibetan plateau the altyn tagh range atr is the northern geological boundary of the tibetan plateau and plays a key role in accommodating its cenozoic lithospheric deformation however knowledge of the structural style and age of uplift of the atr is limited and controversial the qaidam basin in the southeast side of the atr provides an outstanding field laboratory for understanding the history and mechanisms of atr growth this study presents a detailed sedimentological analysis of a 1040 m thick late cenozoic similar to 17 5 0 ma sedimentary sequence from the western qaidam basin together with the analysis of sedimentological data from nearby boreholes and sections our aims were to determine the spatiotemporal evolution of the sedimentary sequences in the study area and to explore their response to late cenozoic tectonic activity in the atr the results show three major intervals of the sedimentary characteristics in the study area similar to 17 16 ma 10 ma and 17 16 ma similar to 16 10 ma and similar to 10 ma during which the atr respectively experienced tectonic uplift fast strike slip motion and intense uplift

two stage evolution model for the altyn tagh fault china the northeastern extension of the altyn tagh fault china beyond the apparently truncated qilian shan has been controversial since the recognition of this large left slip fault we propose that the altyn tagh fault may have been contiguous with the east northeast to northeast trending currently inactive but apparently active during the cenozoic alxa east mongolia fault the latter truncated the beishan orogen to the northwest and the inner mongolia orogen to the southeast the beishan orogen can be correlated with the inner mongolia orogen on the basis of the recognition of three offset petrotectonic units and two offset sutures this correlation requires 400 50 km of left lateral offset along the alxa east mongolia fault identical to the slip along the northern segment of the altyn tagh fault inferred by p molnar and p tapponnier we suggest a two stage model for fault evolution during the first stage 400 km of displacement separated the inner mongolia orogen from the originally contiguous beishan orogen along a continuous altyn tagh alxa east mongolia fault during the second stage the alxa east mongolia fault became inactive and additional offset along the altyn tagh fault has been mainly accommodated by shortening of the qilian shan and the qaidam basin we infer that the first stage of movement along the altyn tagh alxa east mongolia fault system may have begun around oligocene time the region transformed to the second stage of fault movement ca 13 16 ma probably because of thinning of the lithospheric mantle beneath northern tibet the proposed model suggests that the derbur fault in northernmost china and beyond is an extension of the alxa east mongolia fault and has a history of strike slip movement the nearly 400 km of offset on the alxa east mongolia fault may have been accommodated mainly by subduction in the sea of okhotsk

structure and significance of c30 4 methyl steranes in lacustrine shales and oils abstract the structure of the abundant c 30 4 methyl steranes of ancient freshwater lacustrine sediments and derived oils is of interest as their precursors the 4 methyl and in particular 4 23 24 trimethyl sterols dinosterols are reported to be specific to dinoflagellates this study employs a novel liquid crystal gc phase combined with gc ms and gc ms ms to separate and characterise mixtures of c 30 4 methyl sterane standards not resolvable on non polar phases this technique is then applied to identify the c 30 4 methyl steranes in an ancient freshwater sediment a freshwater lacustrine and a marine derived oil a comparison is also made with the 4 methyl steranes in marine sediments containing varying amounts of dinoflagellate cysts the c 30 4 methyl steranes of the freshwater lacustrine samples have been shown to possess a 4 methyl 24 ethylcholestane structure while both 4 methyl 24 ethylcholestanes and 4 23 24 trimethyl 5 h cholestanes dinosteranes were found in the marine dinoflagellate rich sediments while still indicative of dinoflagellates 4 methyl 24 ethyl sterols are generally not the major dinoflagellate sterol and alternative explanations for the abundance of 4 methyl 24 ethylcholestanes in ancient lacustrine sediments should be considered possibly ancient freshwater dinoflagellates synthesised principally the 4 methyl 24 ethyl form alternatively a source from an unrecognized algal class is possible while a source from bacteria which are known to synthesise certain 4 methylsterols is discussed

geochemical and biological marker assessment of depositional environments using brazilian offshore oils abstract a combined geochemical and molecular characterization of a wide selection of oils from the major brazilian offshore basins has been undertaken the elemental sulphur nickel and vanadium and bulk oapi and 13c properties of each sample been considered together with its molecular composition determined using liquid and gas chromatography and quantitative biological marker investigations using gas chromatography mass spectrometry for alkanes the results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups the distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils each group is correlated tentatively with source rocks laid down in a specific depositional regime namely lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate or marine deltaic the diagnostic features that allow this classification are the relative abundance and carbon number distributions of n alkanes pristane phytane ratios sulphur nickel and vanadium contents carbon isotope data the absolute concentrations of hopanes and steranes and their abundance relative to 4 methylsteranes and also the occurrence and abundance of several specific biological markers including 18 h oleanane gammacerane carotane tricyclic terpanes higher acyclic isoprenoids 28 30 bisnorhopane and 25 28 30 trisnorhopane this investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils

intensified aridity of the asian interior recorded by the magnetism of red clay in altun shan ne tibetan plateau abstract the aridity history of monsoon dominated areas has previously been traced by high resolution studies of the well known loess and red clay sequences on the chinese loess plateau however the aridity process further west in china and the differences from the monsoon regime are unclear because no continuous aeolian sequences have been found in those areas here we describe and interpret an 88 4 m thick neogene aeolian sequence containing 40 visually defined brownish red clay and gray caliche nodule layers in the eastern xorhol basin northeast of the tibetan plateau magnetostratigraphic results show that the sequence was deposited between 13 and 2 6 ma the sequence can be divided into two parts with different climate conditions according to magnetic susceptibility ms the lower part 13 11 5 ma indicates a more changeable climate with higher ms values average 15 10 8 m3 kg 1 dominated by magnetite the upper part 10 3 2 6 ma reflects a drier climate with lower stable ms values average 9 5 10 8 m3 kg 1 mainly arising from hematite our results indicate that the intensified aridity of the asian interior started between 11 5 ma and 10 3 ma when ms decreased significantly due to outward growth of the tibetan plateau at around 12 ma together with ongoing global cooling and regression of the neotethys ocean during the cenozoic

structure of the central altyn tagh fault revealed by magnetotelluric data new insights into the structure of the northern margin of the india asia collision abstract the altyn tagh fault atf is a left lateral strike slip fault that forms the northern margin of the tibetan plateau and plays a significant role in accommodating the convergence between the colliding indian and eurasian plates as a part of the fourth phase of the indepth project magnetotelluric mt data were collected across the central segment of the atf to determine the lithospheric scale structure of the fault system dimensionality analyses demonstrated that the mt data can be interpreted using two dimensional approaches but some localized 3 d effects are seen consequently both 2 d and 3 d inversions were carried out and a joint interpretation was made on the basis of these two types of models inversion models revealed two major conductors beneath the qaidam basin qb and altyn tagh range atr respectively the conductive region beneath the qb was interpreted as a ductile layer in the lower crust to upper mantle that might represent flow beneath the western margin of the qb whereas the large scale south dipping conductor beneath the atr is interpreted as a region with high fluid content formed by metamorphism associated with the oblique underthrusting of the tarim block beneath the northern tibetan plateau these fluids migrate upwards through the fault system and have formed serpentinized zones in the crust combining these interpretations a structural model compatible with diverse geophysical observations is proposed in which we suggest the competing end member rigid block model and continuum model are reconcilable with the continuum model locally dominant for the study region as evidenced by a thickened crust

paleozoic multiple accretionary and collisional processes of the beishan orogenic collage in the paper by xiao and others american journal of science v 310 p 1553 1594 1 please substitute figure 16 reproduced here for figure 16 that appears between pages 1573 and 1574 the original figure 16 2 was printed at an improper size figure 3 1 lookup volpage 310

sedimentary evidence against large strike slip translation on the northern altyn tagh fault nw china abstract whether the oblique left reverse northern altyn tagh fault has large cumulative offset 120 km is one of the most controversial issues concerning the deformation mechanics for the northern tibetan plateau in order to obtain material constraints on its total displacement sedimentologic and bedrock provenance analysis of oligocene pleistocene strata on the northern side of the fault was conducted lithofacies analysis and 970 paleocurrent measurements show that these strata were products of fluvial systems originating from south of the fault making it possible to constrain the fault s slip history by establishing cross fault sediment source linkages identification of 5217 conglomerate clasts in the field indicates that major clast types are quartzite 30 50 schist gneiss increasing upsection from 10 to 40 50 and marble decreasing upsection from 20 30 to 30 km strike slip translation on the northern altyn tagh fault and support the model that strain induced by indian indentation has been partitioned into left slip on the altyn tagh fault and reverse dip slip on the northern altyn tagh fault

sea level change and facies development across potential triassic jurassic boundary horizons sw britain the late triassic to early jurassic aged succession of sw britain the penarth and lower lias groups comprises mudstone sandstone and limestone strata deposited in a variety of marine to non marine environments faunal and floral characteristics of these successions have led to the proposal that one location in sw england st audrie9s bay should serve as the global stratotype section and point gssp for the base of the hettangian stage and thus for the triassic jurassic tr j boundary the sections of sw britain have also been used previously to infer sea level change history and relate this to potential kill mechanisms associated with the tr j boundary mass extinction chemostratigraphic biofacies and lithofacies data are used here to suggest alternative models of sea level change in relation to possible tr j boundary horizons in the sections of sw britain a sea level lowstand surface of erosion is inferred to occur within the cotham member of the lilstock formation a unit deposited in an environment that was often subaerially exposed in contrast to previous interpretations the top surface of the overlying langport member here inferred to be deposited on a carbonate ramp of depositional or tectonic origin represents a drowning event of at least regional extent all horizons regarded as plausible levels at which to place the tr j boundary based on fossil distributions lie within strata deposited during relative sea level rise however it is doubtful whether the higher horizons proposed to mark the boundary faithfully record times of true biotic change on a global scale and additionally there is no positive evidence that sea level fall had any relation to the genesis of proposed tr j marker horizons it is unlikely that sea level fall played a significant role in the tr j boundary extinctions in either a local or a global context

reconstruction of the altyn tagh fault based on u pb geochronology role of back thrusts mantle sutures and heterogeneous crustal strength in forming the tibetan plateau 1 reconstructing deformation along the northwestern margin of the tibetan plateau is critical for evaluating the relative importance of microplate versus continuum models of the indo asian collision questions regarding this margin s evolution are as follows 1 what is the total offset along the sinistral altyn tagh strike slip system 2 how has that offset been absorbed in the western kunlun shan 3 why does the n s width of the plateau vary along strike ion microprobe u pb zircon apparent ages of 17 plutons from nw tibet together with regional geologic observations define a discrete e w trending boundary between two tectonic belts that has been offset along the altyn tagh system by 475 70 km kinematic arguments indicate that this offset cannot be the result of north directed thrusting in the western kunlun shan therefore we propose that south directed faulting in the tianshuihai thrust belt both offset the tectonic boundary and produced the asymmetry in the plateau shortening appears to have been absorbed in the upper crust by thin skinned thrusting in the middle lower crust by east directed ductile flow and or subduction and in the mantle by north dipping subduction factors controlling the formation of the south directed thrust system appear to be the contrast between the rigid tarim and the weaker songpan ganzi flysch belt and a mantle suture inherited from late paleozoic subduction the evolution of western tibet leads to a view of continental deformation that integrates elements of the microplate model e g plate like mantle and crust mantle decoupling with aspects of the continuum model weak crustal flow beneath the plateau

late paleozoic to early triassic multiple roll back and oroclinal bending of the mongolia collage in central asia abstract the architecture and mechanics of an orogen can be understood in terms of a system of collages that are characterized by a complex assemblage of multiple components but the fundamental paleogeographic framework and the tectonic relationships between the different components are often insufficiently defined because of unavailable data the central asian orogenic belt caob provides an ideal opportunity to address the fundamental framework of paleogeography and tectonic relationships between the diverse and many components in this huge collage in this paper we review several lines of available evidence which enable us to propose a new tectonic model of huge roll back in the formation of the accretionary tectonics of the mongolian collage in central asia in the early paleozoic the mongolia collage comprised the southern siberian and the tuva mongol oroclines the siberia craton and the mongolia collage jointly formed a giant tadpole shape within the paleo asian and panthanlassic oceans its head siberia was to the south and the tail tuva mongol to the northwest the structures and tectonic zonation of the mongolia collage are characteristic of multiple arcs which have been separately described in detail in different segments southwards from the southern siberia east sayan west sayan gorny altai chara via the lake zone junggar tianshan gobi altai beishan alxa to the manlay hegenshan baolidao solonker segments almost all segments underwent early paleozoic to permian or even triassic frontal subduction and accretion while rifting in the late carboniferous to permian or triassic occurred in the outward oceanward westward advancing mongolian collage therefore we suggest that a huge complex roll back active from the carboniferous to permian or even to late triassic facilitated the formation of the mongolian collage the outward multiple roll back process was compatible and almost coeval with the start of the tuva mongol orocline and rotation of the siberian craton as confirmed by paleomagnetic and structural data during the roll back processes an archipelago paleogeography was formed behind the frontal subduction and accretion in which independent arcs or terranes were amalgamated or collided to form composite arcs or terranes either simultaneously or at slightly different times the roll back process was affected by the collision of the kazakhstan collage along the chara and karamay zones in the early permian the collision of the tarim craton along the south tianshan zone in the early permian the collision of the dunhuang block along the liuyuan zone in the early permian triassic the collision of the alxa block along the qugan qulu zone in the permian and the collision of the north china craton along the solonker zone in the middle late triassic the tectonic styles and architecture of accretionary orogenic belts like the caob are characterized both by the amalgamation of multiple terranes and by oroclinal bending the systematic anatomy of the multiple roll back processes and their interactions with the adjacent collages shed light on the evolving orogenic architecture and the crustal accretionary history of orogens

petrology and geochronology of eclogites from the western segment of the altyn tagh northwestern china abstract the eclogites from the western segment of the altyn tagh occur as lens or boundins within quartzofeldspathic gneisses or pelitic gneisses characterized by amphibolite facies parageneses the petrographic features and reaction textures testify to three main metamorphic stages 1 the peak eclogite facies stage p 15 kbar t 665 880 c 2 the granulitic facies stage p 11 14 kbar t 670 800 c and 3 the amphibolite facies stage p 6 3 9 5 kbar t 619 738 c during decompression the trace element rare earth element and sm nd isotopic data suggest that most of the eclogites have protolith features resembling transitional type t type mid ocean ridge basalt morb the well preserved eclogite was selected for sm nd and u pb isotopic dating the sm nd isotopic data yield a whole rock garnet omphacite isochron of 500 10 ma age the u pb isotopic measurement of zircons from the same eclogite shows that the four grain populations are near concordant and are well plotted on concordia giving a weighted mean age of 503 9 5 3 ma the two different geochronological methods yield a similar age which is interpreted as the peak metamorphic age of eclogites and reflects the existence of a mountain root related to continental subduction during early paleozoic moreover based on the comparison with similar rocks in the northern margin of the qaidam basin a displacement of 350 400 km for the altyn tagh fault have been estimated

leaf wax stable isotopes from northern tibetan plateau implications for uplift and climate since 15 ma abstract the growth of tibetan plateau is considered to have played a key role during the evolution of asian climate our understanding of the relationship between the plateau growth and asian climate changes is limited however due to the scarcity of well dated sedimentary sequences that could provide parallel information of the evolution of elevation and climate here we report a high resolution time series record of the stable hydrogen isotopic composition of leaf wax n alkanes d n alk from a continuous neogene stratigraphic sequence 15 1 8 ma from the qaidam basin on the northern tibetan plateau these data are used to reconstruct the isotopic composition of meteoric waters d m and subsequently applied to interpret the history of paleotopography and climate in qaidam our results indicate four stages in the evolution of hydrology in the qaidam basin in stage i 15 ma to 10 4 ma d m gradually decreases from 24 9 to 75 5 synchronous with a period of active tectonism the estimated topographic growth of 2 1 0 3 km is comparable to the height of qaidam basin relative to the foreland hexi corridor we note that c 3 plants were dominant in this region since the miocene we take this as independent evidence that this area was mountainous before the c 4 expansion in late miocene and pliocene d m variability in subsequent stages appears to be related to shifts in dry and moist conditions and independent of topographical changes a conclusion supported by other independent climatic records on the tibetan plateau high d m values in stage ii 10 4 ma to 6 9 ma are related to severe aridity and stage iii 6 9 ma to 4 1 ma is marked by low d m values suggestive of moist conditions related to the strengthening east asia summer monsoon high d m values in stage iv 4 1 ma to 1 8 ma reflect a climate drier than the present

tomographic evidence for localized lithospheric shear along the altyn tagh fault seismic tomography across the altyn tagh fault at the north edge of the tibetan plateau reveals a low p wave velocity anomaly below the fault down to 140 kilometers this anomaly probably reflects strike slip shear in the lithosphere slip partitioning may also induce a wedge of crust from the tarim basin to plunge into the mantle

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

paleomagnetism and anisotropy of magnetic susceptibility of the tertiary janggalsay section southeast tarim basin implications for miocene tectonic evolution of the altyn tagh range abstract despite receiving considerable attention the nature and timing of cenozoic tectonic evolution of the altyn tagh fault aft remain highly debated here we conducted detailed magnetostratigraphy and anisotropy of magnetic susceptibility ams studies on the cenozoic janggalsay section southeast tarim basin magnetostratigraphy indicates that the measured janggalsay section spans a time interval of 22 11 ma the magnetic declination data suggest that the janggalsay site has rotated significantly counterclockwise 17 2 8 5 from 22 to 17 15 ma while the rotation has terminated from 17 15 to 11 ma the results are consistent with a two stage tectonic model for the atf with a phase of large magnitude strike slip motion along the atf from the oligocene to middle miocene and a second phase of lower amounts of strike slip motion and more widespread contraction since the middle miocene the ams fabric data and sedimentology of the janggalsay section likely indicate the rapid rock uplift of the altyn tagh range since 16 ma

the distribution of molecular fossils derived from dinoflagellates in paleogene lacustrine sediments bohai bay basin china steroids with unconventional side chains in ancient sediments and petroleum have been increasingly used as age diagnostic markers triaromatic dinosteroids and dinosteranes occur widely throughout the eocene oligocene shahejie formation in the southeastern bohai bay basin china consistent with its abundant fossil dinoflagellate assemblages in addition 24 norcholestane biomarkers which commonly appear in marine oils have been found in this lacustrine formation although a firm link has not been established between 24 norcholestane and specific modern taxa both diatoms and dinoflagellates are shown to be likely sources of 24 norcholestanes although the shahejie strata lack intact diatom frustules they do exhibit a good relationship between 24 norcholestane other molecular fossils of dinoflagellates and dinocysts dinoflagellates are important precursor taxa of 24 norcholestanes and the various species identified in eocene oligocene lacustrine shales and mudstones of the shahejie formation are all potential sources of the 24 norcholestanes

major environmental change and bonebed genesis prior to the triassic jurassic mass extinction we present new geochemical and sedimentological data from marginal marine strata of penarth bay south wales uk to elucidate the origin of widespread but enigmatic concentrations of vertebrate hard parts bonebeds in marine successions of rhaetian age late triassic sedimentological evidence shows that the phosphatic constituents of the bonebeds were subjected to intense phosphatization in shallow current dominated settings and subsequently reworked and transported basinward by storms interbedded organic rich strata deposited under quiescent and poorly oxygenated conditions record enhanced phosphorus regeneration from sedimentary organic matter into the water column and probably provided the main source of phosphate required for heavy bonebed clast phosphatization the stratigraphically limited interval showing evidence for oxygen depletion and accelerated p cycling coincides with a negative 4 organic carbon isotope excursion which possibly reflects supra regional changes in carbon cycling and clearly predates the initial isotope excursion characterizing many triassic jurassic boundary strata our data indicate that rhaetian bonebeds are the lithological signature of profound climatically driven changes in carbon cycling and redox conditions and support the idea of a multi pulsed environmental crisis at the end of the triassic possibly linked to successive episodes of igneous activity in the central atlantic magmatic province supplementary material sample positions data table and a detailed stratigraphic log from the upper triassic of penarth bay south wales uk are available at http www geolsoc org uk sup18510

a molecular stratigraphic approach to palaeoenvironmental assessment and the recognition of changes in source inputs in marls of the mulhouse basin alsace france principal components analysis pca has been used to investigate changes in concentrations of the components of the hydrocarbon fractions extracted from 71 marl samples selected to cover two total organic carbon toc maxima in the lower part of the salt iv formation a lower oligocene evaporitic sequence from the mulhouse basin france the analysis indicates that the fractions can be ascribed as lying between two end member distributions the changes in these distributions are gradual suggesting that they resulted from fairly gradual changes in the depositional palaeoenvironment these changes are related to increased algal productivity associated with the evolution of a restricted lacustrine environment through to one with a greater marine influence systematic variations in the concentrations of selected components relative to the toc profile point to a repeated sequential evolution in the biological assemblage during deposition of the sequence

structural and sedimentary characteristics of the liangjia wangchang strike slip region yitong basin china abstract the yitong basin a typical strike slip basin is part of the northern segment of the world famous tanlu strike slip fault area in china research is needed to understand how the strike slip tectonic environment affects the development of structures and depositional systems within the basin the aim of this paper is to analyze how the right lateral strike slip movement of the northwestern boundary faults in this region controls extensional faulting and to analyze differences in two main sedimentary sequences termed sysq1 and sysq2 that result from strike slip movement the study is based on geological and geophysical data the following conclusions are drawn 1 the two periods of strike slip movement of the boundary fault generated two episodes of extensional fault inside the basin the extensional faults have a characteristically episodic activity related to the episodic strike slip movement the extensional faults have small fault throw and their activity lags behind the strike slip movement of the northwestern boundary faults 2 the strike slip movement of the boundary faults generated the extensional faults inside the basin and changed the locus of depocenters with complimentary changes in the paleogeomorphology and in the distribution of depositional facies it is this strike slip movement that caused the differences in sedimentary and structural characteristics between sequences sysq1 and sysq2

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

new discovery of early jurassic radiolarians from luoqu xigaze southern tibet and its geological significance abstract numerous moderately preserved radiolarians of tethyan affinity were extracted from a purple red chert sample from the luoqu section on the southern side of the yarlung tsangpo suture zone in the xigaze area southern tibet ninety three species belonging to 35 genera are recognized of which one is described as citriduma pentaptera sp nov most of them are reported from tibet for the first time significantly this radiolarian assemblage of nassellarians subordinate spumellarians and rare entactinarians can be compared with those in oman japan oregon and queen charlotte islands and is further assigned to the eucyrtidiellum nagaiae praeparvicingula tlellensis zone of late pliensbachian in age this indicates that the pelagic deposits of the neo tethys ocean in the xialu area were laid down at least during or since the late pliensbachian much earlier than the aalenian age previously considered

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

geomorphic evidence for active faulting in the altyn tagh and northern tibet and qualitative estimates of its contribution to the convergence of india and eurasia a brief traverse across the altyn tagh and kunlun in northern tibet revealed abundant evidence for recent crustal deformation there from ridges offset roughly 10 m and from fresh mole tracks 40 cm or more high along the altyn tagh strike slip fault we conclude that a large earthquake occurred in the past few hundred years accordingly the rate of slip could be relatively high 30 20 mm yr active reverse or thrust faults mark the bases of several mountain ranges in the altyn tagh and kunlun where the neighboring basins lie at elevations less than 4000 m therefore roughly north south crustal shortening appears to be occurring there probably at a rate of several millimetres per year the crustal shortening accommodated by strike slip and reverse or thrust faulting appears to account for a significant part 10 25 of india s convergence with eurasia the broad zone of crustal shortening in northern tibet indicates that the areal extent of the plateau is increasing northward by crustal thickening on its northern margin

riser diachroneity lateral erosion and uncertainty in rates of strike slip faulting a case study from tuzidun along the altyn tagh fault nw china 1 at late quaternary timescales offset fluvial terrace risers are among the most common landforms used to determine rates of strike slip faulting although diachroneity in the age of riser segments on opposite sides of the fault has been noted previously an unexplored source of uncertainty associated with deriving slip rates from these markers centers on quantifying the size of the displacement uncertainty such diachroneity introduces to evaluate the impact of riser diachroneity we investigated the tuzidun site 37 73 n 86 72 e along the cherchen he reach of the active central altyn tagh fault the east bank of the channel is flanked by a left laterally offset terrace riser while the measured offset is 54 3 m geochronologic measurements and analysis of riser topography indicate that the downstream riser segment formed between 6 0 0 8 ka and 5 7 0 4 ka while the upstream riser segment may have been laterally refreshed as recently as 0 5 0 2 ka a valley wall on the west bank of the channel places a maximum limit of 38 6 m on the amount of possible lateral erosion of the upstream riser this bound in turn limits the total offset since formation of the downstream riser to range from 54 3 to 89 7 m together these observations bracket the millennial altyn tagh fault slip rate to range from 9 0 1 3 to 15 5 1 7 mm a 1 more generally this investigation shows that the observed riser displacement does not necessarily correlate with the age of either riser segment downstream or upstream of the fault in cases where one segment is displaced while the other is subjected to lateral erosion if this diachroneity goes undetected erroneous slip rate measurements are likely to result

climatic influences on the paleogene evolution of alkenones application of the alkenone paleotemperature proxy uk 37 for marine sediments is typically constrained by three factors i an absence of alkatrienones in sediments deposited where ocean temperatures exceed 28 c ii loss of alkenones in thermally altered sediments and iii poor preservation of alkenone signals due to oxidative degradation in addition there appears to be a temporal limit on the occurrence of alkatrienones which are conspicuously absent in all alkenone containing sediments from the early aptian to the immediate aftermath of the early eocene climatic optimum eeco when they first appeared in arctic ocean sediments compilation of reported and previously unpublished alkenone distributions for the paleogene coupled with assessment of co occurring calcareous nannoplankton genera within the noelaerhabdaceae provide evidence that evolutionary developments in alkenone occurrences include biosynthetic responses likely triggered by climate change the timing of emergence of alkatrienones post eeco and their subsequent appearance at all latitudes during the middle eocene accompanies expansion of the calcareous nannoplankton genus reticulofenestra coincident with significant climate driven changes in oceanic conditions including i modification of trophic structure associated with weakened thermal stratification ii higher productivity facilitated by enhanced nutrient influx and iii changes in seasonality initially at high latitudes related to greater latitudinal temperature gradients collectively these changes would serve to favor eurythermal eurytrophic algae like reticulofenestra with a biomechanism to store energy through production of lipid bodies rich in alkenones during episodes of higher nutrient availability this ability likely enhanced the viability of this marine haptophyte when nutrients were limiting ultimately ensuring its evolutionary success

stable isotopic constraints on the tectonic topographic and climatic evolution of the northern margin of the tibetan plateau abstract this study presents oxygen and carbon isotopic records from lacustrine paleosol alluvial and fluvial carbonate sampled in thirteen cenozoic sedimentary sections that span the northern margin of the tibetan plateau isotopic analyses of 1475 carbonate samples yield 18 o values that range from 13 1 to 38 9 smow and 13 c values range from 11 5 to 3 7 pdb based on these analyses we see two isotopic trends regionally we interpret a paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region s drainages as they tapped waters from a growing tibetan plateau to the south of the study area we interpret a neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters which increased basin isolation aridity and temperatures the timing of inferred initiation of uplift in this region is consistent with structural thermochronological and sedimentological evidence for a tectonic transition in the early and middle miocene from accommodation of india eurasia convergence through extrusion along the altyn tagh fault to accommodation of convergence through active shortening and mountain building in this region this study also supports tectonic models for the differential uplift of the tibetan plateau in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central tibetan plateau

early paleozoic to devonian multiple accretionary model for the qilian shan nw china abstract the qilian shan located in the northern tibetan plateau of nw china has an excellent record of early to middle paleozoic subduction accretion that resulted from convergence between the alax and qaidam blocks but there is no consensus about its detailed tectonic history this paper summarizes its tectonic divisions and discusses its tectonic evolution from the cambrian to devonian the belt has the following tectonic divisions in the far north the southern passive margin of the alax block is juxtaposed against an early cambrian to ordovician marianan type intra oceanic arc north qilian the north qilian arc is separated from a japanese type arc central qilian to the south by a high pressure metamorphic belt composed mostly of ophiolitic slices and oceanic crusts the central qilian is bounded to the south by a wide melange zone south qilian consisting of ophiolitic slices and continental margin sequences farther to the south lies the oulongbuluk microcontinent that is separated from the qaidam block and farther south by an ultrahigh pressure metamorphic belt tectonostratigraphic analysis together with geochemical geochronological and geophysical data indicates a complex evolution by subduction accretion processes from the cambrian to the devonian before final amalgamation and docking to the northern alax block this model solves the long lasting discussion on the polarity of subduction in paleozoic time this multiple subduction accretion history sheds light on the continuity of paleozoic sutures along the qilian shan and the nature of the altyn tagh fault and thus contributes to an improved understanding of the tectonic architecture of central asia

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

low temperature thermochronometry along the kunlun and haiyuan faults ne tibetan plateau evidence for kinematic change during late stage orogenesis the tibetan plateau is a prime example of a collisional orogen with widespread strike slip faults whose age and tectonic significance remain controversial we present new low temperature thermochronometry to date periods of exhumation associated with kunlun and haiyuan faulting two major strike slip faults within the northeastern margin of tibet apatite and zircon u th he and apatite fission track ages which record exhumation from 2 to 6 km crustal depths provide minimum bounds on fault timing results from kunlun samples show increased exhumation rates along the western fault segment at circa 12 8 ma with a possible earlier phase of motion from 30 20 ma along the central fault segment at circa 20 15 ma and along the eastern fault segment at circa 8 5 ma combined with previous studies our results suggest that motion along the haiyuan fault may have occurred as early as 15 ma along the western central fault segment before initiating at least by 10 8 ma along the eastern fault tip we relate an 250 km wide zone of transpressional shear to synchronous kunlun and haiyuan fault motion and suggest that the present day configuration of active faults along the northeastern margin of tibet was likely established since middle miocene time we interpret the onset of transpression to relate to the progressive confinement of tibet against rigid crustal blocks to the north and expansion of crustal thickening to the east during the later stages of orogen development

molecular indicators of palaeoenvironmental conditions in an immature permian shale kupferschiefer lower rhine basin north west germany from free and s bound lipids a study of the distributions of free and s bound biomarkers and their 13c values in the extract of a bulk sample of the permian kupferschiefer from the lower rhine basin has been carried out to provide a more detailed characterization of the biological inputs the distributions and isotopic compositions of selected components released from nickel boride desulphurization have been compared with those of components in the free fraction the free biomarkers occur in greater abundance than their s bound counterparts the distribution and carbon isotopic composition of both free and bound components in the extract indicate a major cyanobacterial and algal input likewise the free and bound aromatic hydrocarbons contain components which reveal an origin from the carotenoids of chlorobiaceae green sulphur bacteria providing molecular evidence for the occurrence of photic zone anoxia in the water column most of the components in the complex mixture of mono di tri and tetra aromatics in the free aromatic hydrocarbon fraction result from cyclization and aromatization reactions

slowing extrusion tectonics lowered estimate of post early miocene slip rate for the altyn tagh fault abstract determination of long term slip rate for the altyn tagh fault is essential for testing whether asian tectonics is dominated by lateral extrusion or distributed crustal shortening previous slip history studies focused on either quaternary slip rate measurements or pre early miocene total offset estimates and do not allow a clear distinction between rates based on the two the magmatic and metamorphic history revealed by shrimp zircon dating of clasts from miocene conglomerate in the xorkol basin north of the altyn tagh fault strikingly matches that of basement in the southern qilian shan and northern qaidam regions south of the fault this match requires that the post early miocene long term slip rate along the altyn tagh fault cannot exceed 10 mm year supporting the hypothesis of distributed crustal thickening for post early miocene times this low long term slip rate and recently documented large pre early miocene cumulative offset across the fault support a two stage evolution wherein asian tectonics was dominated by lateral extrusion before the end of early miocene and since then has been dominated by distributed crustal thickening and rapid plateau uplift

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

oligocene miocene tectonics and sedimentation along the altyn tagh fault northern tibetan plateau analysis of the xorkol subei and aksay basins abstract tertiary basins adjacent to the northern edge of the tibetan plateau include both giant intracontinental sedimentary basins such as tarim and qaidam and smaller basins directly related to the evolution of the altyn tagh strike slip fault system and nearby fold thrust belts three examples of these smaller basins that formed during early evolution of the altyn tagh fault system are the xorkol aksay and subei basins the xorkol basin was the site of nonmarine siliciclastic sedimentation in alluvial fan playa and fluvial environments from at least the mid oligocene through the miocene sediment was delivered to the basin from source areas uplifted by basin bounding thrust faults and from the opposite side of the altyn tagh fault the age of the aksay basin is more poorly constrained but it also contains oligocene miocene nonmarine clastic strata that were derived from the southern side of the altyn tagh fault and adjacent thrust fault bounded uplifts the subei basin is characterized by s

molecular isotopic evidence of environmental and ecological changes across the cenomanian turonian boundary in the levant platform of central jordan abstract we evaluated the structure of planktonic communities and paleoenvironmental conditions throughout the cenomanian turonian oceanic anoxic event oae2 by studying bulk geochemical properties and the molecular isotopic composition of source specific hydrocarbons from organic rich sediments deposited in an intrashelf basin at the levant platform central jordan high concentrations of desmethyl and 4 methylsteranes as well as dinosteranes indicate that marine algae including dinoflagellates were the main primary producing organisms the presence of 2 methylhopanes and 13 c enriched hopanes in addition to isotopically enriched aryl isoprenoids evidenced the contribution of cyanobacteria and green sulfur bacteria respectively additionally variable but fairly low 15 n values during oae2 suggest the occurrence of diazotrophy as a likely important process fueling primary production during oae2 in this stratified anoxic continental platform variations in the relative contribution of biomarkers revealed changes in planktonic communities associated with sea level change and water column stratification oae2 was characterized by strong stratification anoxic bottom waters and a deep chemocline as evidenced by high gammacerane and homohopane indices and the absence of photic zone euxinia pze markers respectively however the presence of isorenieratane and its derivatives in post oae black shales points to a shoaling of the chemocline and to pze this interval was also characterized by an exceptionally high abundance of chlorophyll derived pristane and phytane up to 2 mg g 1 toc likely as a result of highly enhanced primary production and organic matter preservation remarkably this high productivity event co occurs with an exceptionally high abundance of calcispheres reported elsewhere to be part of a global bio event

from sea level to high elevation in 15 million years uplift history of the northern tibetan plateau margin in the altun shan approximately 1300 in of oligocene miocene clastic strata are exposed along the miran river in the southeastern tarim basin where the adjacent altun shan form the topographic escarpment of the northern tibetan plateau the sedimentary section is faulted against proterozoic rocks of the altun shan in the footwall of the south dipping oblique reverse northern altyn tagh fault oligocene lower miocene strata consist of fine grained rocks that record low gradient depositional systems mid miocene and younger rocks consist of coarse conglomerate derived from the altun shan and deposited by high gradient depositional systems the change to coarse high gradient depositional systems with detrital source areas coincident with the modern miran river drainage is interpreted to mark the onset of uplift of the altun shan on the northern altyn tagh fault and its erosional exhumation the age of the change from pre orogenic to synorogenic sedimentation is constrained by a foraminifera assemblage at the base of the conglomeratic section that includes early middle miocene planktonic foraminifera this interpretation is also supported by apatite fission track and u th he ages and thermal models that indicate rapid miocene cooling and hence rapid exhumation of the altun shan in addition to defining the age of the synorogenic section the foraminifera assemblage contains planktonic taxa indicating a connection to open marine waters and benthic assemblages typical of brackish to near sea level paleobathymetry thus micropaleontologic evidence demonstrates that the miran river locality now at 1400 in elevation was at sea level approximately 15 million years ago thus in addition to constraining the age of surface uplift and exhumation of the altun shan the principal mountain range of the tibetan plateau in this region as 15 to 16 ma the foraminifera assemblage indicates that the se tarim basin off the northern edge of the plateau had an average surface uplift rate of nearly 100 m m y for the past 15 million years these results suggest that shortening in the altun shan and uplift of the range significantly post dated the initiation of large scale strike slip on the altyn tagh fault and that regional surface uplift mechanisms operated in the tarim basin beyond the margins of the tibetan plateau

evidence of miocene crustal shortening in the north qilian shan from cenozoic stratigraphy of the western hexi corridor gansu province china new sedimentologic stratigraphie and compositional data from the paleogene neogene stratigraphie succession exposed in the northwest hexi corridor and within the north qilian shan provide evidence to suggest that crustal shortening in the north qilian shan fold thrust belt initiated during die miocene the section is composed of four lithostratigraphic units oligocene miocene fine to coarse grained unit 1 miocene conglomeratic unit 2 and pliocene pleistocene conglomeratic units 3 and 4 unit 3 lies in angular unconformity over both units 1 and 2 and unit 4 contains a progressive unconformity the onset of conglomerate deposition at the base of unit 2 suggests an increase in depositional energy which we interpret as me result of proximal orogenesis in the north qilian shan fold and tiirust belt supporting evidence includes the appearance of strongly northeast trending paleocurrents indicat ing paleoflow away from the qilian shan clast lidiologies that match sources in the north qilian shan and sandstone with detrital framework modes that indicate a recycled orogen source in contrast unit 1 contains paleocurrent indicators that are variable but generally trend northward and sandstone and clast compositions which are more diagnostic of a continental block source detrital zircon age determinations from unit 1 are also not consistent with a source in the north qilian shan rather they suggest a provenance in hinterland regions within the south qilian shan and north qaidam terranes in sum these results are all consistent with initiation of proximal uplift of the north qilian shan during deposition of the gradational transition from unit 1 to unit 2 demonstrating shortening in the qilian shan before die late miocene this comprehensive study tightens our understanding of when far field stress related to the india eurasia continent continent collision reached the northeastern edge of the tibetan plateau

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

occurrence and composition of solid bitumens from the bulonggoer devonian paleo oil reservoir north xinjiang china abstract the bulonggoer paleo oil reservoir bpr on the northwest junggar basin is the first devonian paleo oil reservoir discovered in north xinjiang china solid bitumens occur within sandstone pores and as veins filling fractures samples of both types were analyzed using stable carbon isotope and reflectance measurements as well as molecular biomarker parameters the extremely positive 13 c values and biomarker indicators of depositional environment lithology such as pristane phytane pr ph c 29 c 30 hopane diasteranes regular steranes and dibenzothiophene phenanthrene ratios indicate a siliciclastic source for the bpr and their deposition in a highly reducing hypersaline environment the presence of long chain n alkanes and abundant tetracyclic diterpanes c 20 c 21 tricyclic terpanes and perylene are indicators of higher plant organic matter input moreover the bimodal distribution of c 27 c 28 29 regular steranes and abundant methyltriaromatic steroids also support a contribution of microalgae as well as higher plants organic matter the similar molecular composition and thermal maturity parameters indicate that the reservoir and veined solid bitumens were altered from a common paleo petroleum which originated from peak oil window matured source rocks all solid bitumens from the bpr are characterized by relatively low bitumen reflectance values rb

organic facies variations in the westbury formation rhaetic bristol channel sw england abstract despite their dark colour laminated fabric and dysoxic character the thermally immature shales of the rhaetic westbury formation of the bristol channel area typically have total organic carbon toc values of only 1 0 1 5 and hydrogen indices hi 200 variations in toc and hi are correlated with the amorphous organic matter aom fluorescence but not the aom suggesting that redox related variations in aom preservation control the organic facies the diameter of equidimensional black wood phytoclasts decreases in intervals with higher toc and hi suggesting an association with lower energy depositional conditions such intervals also show a relative increase in light brown wood probably a reflection of more humid onshore conditions and lower phytoclast oxidation at source phytoc values suggest the input of terrestrial om was relatively low and stable during westbury deposition indicating a distal setting removed from fluviodeltaic sediment sources

geochemical evidence of organic matter source input and depositional environments in the lower and upper eagle ford formation south texas abstract late cretaceous source rocks in the south texas eagle ford formation were characterized based on geochemical features of the iona 1 core which penetrates the lower and upper eagle ford formation this set of immature samples provides a detailed record of the variation of organic matter om sources across different depositional facies our results show that organic matter rich shales are dominated by marine type ii kerogen lower eagle ford lef contains high sulfur kerogen type ii s with s c 0 04 and a minor contribution of terrestrial om is evident in the upper eagle ford uef combined geochemical data from iona 1 core samples based on bulk geochemical rock properties residual oil chromatography and biomarker analyses reveal that the total organic carbon content and extractable bitumen content in the lef are higher than in the uef redox sensitive biomarkers demonstrate that sulfur rich photic zone anoxia euxinia developed in the lef and that persistent oxygenation occurs during deposition of the uef sulfur rich kerogen in the lef in turn generates medium high sulfur containing oils up to 2 6 as a consequence of the elevated sulfur contents in the lef oil bitumen generation initiated earlier and at lower maturity levels than in the uef high levels of anomalous 22s 22s 22r homohopane ratios and 20s 5 14 17 steranes have been observed in the lef interval which is controversial because of the low maturity level indicated by most bulk geochemical thermal maturity parameters including tmax calculated ro 0 45 and ts ts tm as well as c29ts c29ts c29 hopane and c29 sterane ratios these anomalously high thermal maturity parameters are more likely caused by enhanced isomerisations due to high organic sulfur content under reducing depositional environments in the lef rather than by thermal maturation hypothetical diagenetic pathways for the sulfurisation of homohopanoids and steroids are proposed to explain their abnormal isomerisations in the lef

faulted terrace risers place new constraints on the late quaternary slip rate for the central altyn tagh fault northwest tibet the active left lateral altyn tagh fault defines the northwestern margin of the tibetan plateau in western china to clarify late quaternary temporal and spatial variations in slip rate along the central portion of this fault system 85 90 e we have more than doubled the number of dated offset markers along the central altyn tagh fault in particular we determined offset age relations for seven left laterally faulted terrace risers at three sites kelutelage yukuang and keke qiapu spanning a 140 km long fault reach by integrating surficial geologic mapping topographic surveys total station and tripod light detection and ranging t lidar and geochronology radiocarbon dating of organic samples 230 th u dating of pedogenic carbonate coatings on buried clasts and terrestrial cosmogenic radionuclide exposure age dating applied to quartz rich gravels at kelutelage which is the westernmost site 37 72 n 86 67 e two faulted terrace risers are offset 58 3 m and 48 4 m and formed at 6 2 6 1 ka and 5 9 3 7 ka respectively at the yukuang site 38 00 n 87 87 e four faulted terrace risers are offset 92 12 m 68 6 m 55 13 m and 59 9 m and formed at 24 2 9 5 ka 6 4 5 0 ka 5 1 3 9 ka and 24 2 6 4 ka respectively at the easternmost site keke qiapu 38 08 n 88 12 e a faulted terrace riser is offset 33 6 m and has an age of 17 1 2 2 ka the displacement age relationships derived from these markers can be satisfied by an approximately uniform slip rate of 8 12 mm yr however additional analysis is required to test how much temporal variability in slip rate is permitted by this data set

organic carbon as a palaeoenvironmental indicator in the marine realm recent developments in biogeochemistry have made accessible all information currently known to be present in sedimentary organic compounds i e the carbon skeleton structure the positions of functional groups and stable carbon isotope ratios this combined information has strengthened the applications of sedimentary organic compounds as biomarkers and palaeoenvironmental indicators this review summarizes the most important biomarkers and their applications in reconstructing marine palaeoenvironments and processes the marine environment is characterized by the combined presence of specific compounds such as organic sulphur compounds dinosteroids 24 n propylsteroids even in trace amounts high amounts of c hbi hydrocarbons and the absence of long chain n alkanes with odd over even predominance bicadinanes and specific higher plant triterpenoids e g oleanane furthermore palaeoenvironmental conditions such as photic zone anoxia hypersalinity microbial sulphate reducing activity algal blooming palaeo upwelling and palaeo surface seawater temperature are indicated by molecular and or isotopic characteristics biomarkers from terrestrial sources are included because land derived organic matter is an important contributor to coastal and shallow marine environments a short case study within a holocene terrestrial marine setting florida bay usa is also presented to illustrate the reconstruction of transgressive regressive trends using selected organic compounds

stable isotope records of cenozoic climate and topography tibetan plateau and tarim basin we seek to better understand growth of the tibetan plateau and associated climate change by presenting the first regionally extensive set of oxygen isotope data obtained from ca 40 m y of cenozoic strata from a 700 000 km2 area ranging from the northern edge of the tibetan plateau northward across the entire tarim basin our results reveal a previously unrecognized large positive isotope shift from eocene to oligocene which we suggest results from initial topographic growth of the himalayan tibetan system and attendant reorganization of climate by this growing mountain belt a negative isotopic shift recorded in miocene strata may reflect retreat of the neotethyan sea from the tarim basin as well as enhanced elevation of the himalaya tibetan plateau region and the rise of the tian shan which diverted moisture bearing westerlies and deepened aridity in the tarim basin and the northern tibetan plateau

intracrustal detachment within zones of continental deformation geologic mapping of active to recently active geologic structures in panamint valley western united states and in the haiyuan region and northern tibetan plateau china suggests detachment in the middle and lower crust on a scale of tens of kilometres to at least several hundred kilometres detachment occurs similarly in predominantly extensional panamint valley and in predominantly compressional china environments it involves structures with displacements of more than 10 km and displacement rates of more than 3 mm yr perhaps more than 10 mm yr the steeply dipping strike slip faults present in all three areas hunter mountain fault haiyuan fault and altyn tagh fault zone terminate in zones of extension or compression and geometric relations indicate that all structures including strike slip faults are thin skinned and restricted to the upper crust in panamint valley and in the haiyuan region deformation within these systems can be reconstructed in three dimensions displacement on the strike slip faults is absorbed by extension or compression occurring at the termination of the faults so strike slip displacement is roughly equal to and in the same direction as shortening or extension we propose that left slip on the altyn tagh fault zone in northern tibet is similarly absorbed by shortening southeast of the fault zone within the qaidam basin and the nan shan

dinosteranes 4 23 24 trimethylsteranes and other biological markers in dinoglagellate rich marine sediments of rhaetian age abstract alkane biological marker distributions and concentrations have been determined in 18 samples from a section of rhaetian age from the bristol trough and a quantitative micropalaeontological analysis carried out taking into account previous geological investigations of the sequence three end member depositional settings have been recognised from changes in total organic carbon content the biological markers and the micropalaeontological composition these depositional environments are attributed as follows the first which occurs in the lower part of the section corresponds to deposition in a supratidal sabkha type setting with the major organic input being of allochthonous origin the second also in the lower part of the section indicates the occurrence of periods of marine incursion with enhanced salinity resulting from evaporation in the upper part of the section marginal marine conditions are apparent with higher organic carbon biological marker and amorphous organic matter contents at the top suggesting the establishment of more stable conditions of oxygen depletion some sediments in the sequence are notable for containing an abundance of cysts of rhaetogonyaulax rhaetica one of the oldest marine dinoflagellates comparison of microfossil abundances with hydrocarbon abundances extends the circumstantial evidence for the dinophyceae being the major biological source of dinosteranes 4 23 24 trimethylcholestanes and some other 4 methyl steranes in marine sediments the presence of dinosteranes and their 24 ethyl counterparts extends the stratigraphic range of occurrence of such components back to the rhaetian c 31 methyl steranes in the sediments from the second depositional setting are tentatively assigned a 4 22 23 24 tetramethyl sterane skeleton and a dinoflagellate origin