intracontinental subduction and palaeozoic inheritance of the lithosphere suggested by a teleseismic experiment across the chinese tien shan teleseismic tomography across the chinese tien shan shows that seismic wave speeds in the lithosphere beneath central tien shan are high and therefore the lithosphere is not weaker than that beneath the adjacent undeformed tarim and junggar basins there is evidence for significant velocity contrasts within the lithosphere that are presumably inherited from the palaeozoic collision history the high velocity thick yili block observed underneath the northern tien shan is a clue for shortening by a intracontinental subduction the observed geometry is consistent with a simple model of intracontinental subduction and suggests that during orogeny the lithosphere has remained heterogeneous and has deformed along existing planes of weakness rather than by homogeneous thickening of a particularly weak lithosphere

deformations of the near surface part of the earth s crust by seismologic and geodetic data obtained on baikal geodynamic polygons abstract the tunkin geodynamic polygon is taken where the deformation tensor components approximately 10 4 for the earth s crust upper layers along with the relative displacements of the blocks in the fault zone have been determined based on the application of the theory of small deformations and on an experimental base of repeated geodetic measurements a comparative analysis of the surface deformation calculated by geodetic measurements with respect to the deep seated deformations obtained from seismic foci mechanisms is given

the grace satellite gravity and geoid fields in analysing large scale cratonic or intracratonic basins the recently released gravity potential field development derived from the gravity recovery and climate experiment satellite allows an unprecedented opportunity to use the gravity field to make global comparisons of structures of geological interest the spatial resolution of the gravity field is sufficiently good to map large scale or intracratonic and cratonic basins as the areal extent of these basins is 0 5 x 10 6 km 2 and greater we present the gravity anomaly bouguer geoid and terrain corrected geoid fields for a selection of nine large scale basins and show that the satellite derived field can be used to successfully identify distinctive structures of these basins e g extinct rifts underlying the basins and generally the isostatic state the studied basins are the eastern barents sea west siberian tarim congo michigan amazon solimoes parnaiba and parana basins we complete the mapping of the gravity field with a description of the basins in terms of areal extension and depth sedimentary age and presence and age of volcanism interpretation of the satellite gravity anomalies and considerations regarding the crustal thickness as known from seismic investigations allows us to conclude that for the greater part of the basins there is evidence for high density material in the lower crust and or upper mantle this density anomaly is at least partly compensating for the low density sedimentary infill instead of the crustal thinning mechanism for our selection of basins crustal thickness variations and moho topography cannot be considered as mechanisms of compensation of the sedimentary loading which is a clear difference to well defined rift basins

organic matter rich shales of china abstract organic matter rich shales are the main target rocks for unconventional oil and gas exploration and development across the world in china shale gas geological resources are estimated as approximately 110 1012 m3 with recoverable gas reserves of ca 20 1012 m3 recoverable shale oil reserves are estimated as ca 5 109 t a total 35 important organic matter rich shale units have been recognized from mesoproterozoic to cenozoic strata across the entire china these shales are categorized according to their origin under marine marine nonmarine transitional and lacustrine conditions shales of marine origin with ca 9 1012 m3 recoverable resources dominate china s potential in terms of total volume of organic carbon currently the most favorable marine shales for oil and gas exploration are found in the sichuan basin within the lower cambrian qiongzhusi formation and in the wufeng longmaxi formations of uppermost ordovician through lower silurian a fortuitous combination of of sea level variations of paleo productivity of tectonic activity causing development and migration of partially closed deep basin depocenters and of sediment accumulation rates controlled the extensive deposition and distribution of organic matter rich shales in these wufeng and longmaxi formations organic matter rich shales in marine nonmarine transitional facies associated with coal measures occur in north china within the carboniferous and permian and in south china within the permian these carboniferous permian organic matter rich shales are important source rocks for the gas fields in the ordos and sichuan basins abundant organic rich shales are also widely distributed within coal bearing clastics and coal measure shales of fluvial lacustrine and swamp facies in upper triassic to middle jurassic successions of many basins lacustrine organic rich shales were deposited during the permian through neogene in various freshwater to saline lake settings lacustrine organic matter rich shales are the main oil source rocks in the songliao bohai bay ordos and junggar basins lacustrine algae contributed to the rain of organic matter and the preservation of organic matter and distribution of organic rich shale was controlled by lake currents water depth and oxygen poor conditions with enhanced preservation when buried by turbidity currents algal blooms were partly induced by trace nutrients from volcanic ash falls in all of these lacustrine basins seawater intrusion into the freshwater lake of the songliao basin promoted some episodes of black shales saline lacustrine basins such as middle permian junggar basin contain organic rich dolomite mudstone that mainly formed during hot climate conditions when the lakes had high salinity and stratified water columns that deprived the bottom waters of oxygen thereby preserving massive amounts of organic matter laminated calcite rich mudstone in the saline lacustrine settings formed in more brackish waters under stable warm conditions and weak biological activity the modeling of the factors controlling the distribution of organic matter rich shales within china s basins is important for the exploration and development of unconventional oil and gas resources

carbon isotope chemostratigraphy and implications of palaeoclimatic changes during the cisuralian early permian in the southern urals russia abstract in order to meet the requirements for potential gssps in the cisuralian series early permian isotopic chemostratigraphy from the carboniferous permian boundary to middle artinskian using bulk carbonates was investigated under high resolution biostratigraphical and new geochronologic constrains from three gssp candidate sections at usolka kondurovsky and dal ny tulkas in the southern urals russia a gradually increasing trend in carbonate carbon isotope 13 c has been observed in the interval from the base of asselian to early sakmarian which is generally consistent in timing with the increasing development of glacial iii or p1 from the latest carboniferous to early sakmarian early permian which prevailed in southern gondwana an excursion with double negative shifts in 13 c value is present around the asselian sakmarian boundary in both the usolka and kondurovsky sections which may have great potential to serve as chemostratigraphical marks for intercontinental correlation the following highly positive excursion of 13 c in early sakmarian indicates the maximium expansion of glacial iii or p1 the negative 13 c shift in the middle sakmarian is possibly related to the quick collapse of glacial iii or p1 on the gondwanaland this negative shift is largely correlative with those documented in other areas of russia the north american craton and south china but further precise biostratigraphical and geochronologic constrains are neccessary to confirm this global signal the late sakmarian is characterized by a strong oscillation stage of 13 c which probably indicates a complex climate transition marked by smaller alternating glacial interglacial transitions during glacial p2 superimposed on an overall warming trend the sharp negative 13 c shift around the sakmarian artinskian boundary at the dal ny tulkus section is difficult to interpret this is followed by long term low values 13 c values in the artinskian at the dal ny tulkas section might result regionally from the enhanced input of organic carbon after the melt out of ice sheets and the subsequent degradation and isotopic refractionation of the microbial chemosynthetic processes on the buried organic matter

dissecting calathium microbial frameworks the significance of calathids for the middle ordovician reefs in the tarim basin northwestern china abstract as an obconical macrofossil with porous double wall calathium was commonly present in reefs of early to early middle ordovician age the calathium bearing reefs thrived globally during the early ordovician but this ecosystem collapsed in middle ordovician a rare case of calathium microbial reefs was found from the middle part of the yijianfang formation darriwilian late middle ordovician of the bachu area located in the northwestern margin of the tarim basin northwestern china surrounded by bioclastic grainstones patch reefs here are well developed and vary in size with 1 4 m in thickness and 2 18 m in diameter three facies types are distinguished within the reef limestones 1 calathium microbial framestone 2 echinoderm calathium bafflestone and 3 bryozoan microbial bindstone as a dominant type the calathium microbial framestone shows a three dimensional skeletal framework that is mainly constructed by calathium and stabilized by microbialites although most specimens are toppled calathium displays well developed lateral outgrowths which connected individuals of the same species morphological characters of calathium in thin sections show that calathids are hypercalcified sponges rather than receptaculitid algae unlike the early ordovician lithistid sponge calathium reefs the tarim reefs studied herein contain very few lithistid sponges instead bryozoans are fairly common and act as the most important non microbial encrusters attaching to the walls of calathium noticeably the co occurrence of pelmatozoans and calathium is similar to those reported from late ordovician calathids echinoderm reef communities from tennessee the presence of calathium microbial reefs in tarim indicates that locally calathids were major reef builders at least before the latest middle ordovician

retreat of northern margins of george vi and wilkins ice shelves antarctic peninsula the george vi and wilkins ice shelves are considered at risk of disinteg ration due to a regional atmospheric warming trend on the antarctic peninsula retreat of the northern margin of the george vi ice shelf has been observed previously but the wilkins ice shelf was thought to be stable we investigated the positions of the northern fronts of these shelves from the literature and looked for changes on 1974 landsat and 1992 and 1995 european remote sensing satellite ers synthetic aperture radar images our investigation shows that the northern george vi ice shelf lost a total of 906 km 2 between 1974 and 1992 and an additional 87 km2 by 1995 the northern margin of the wilkins ice shelf lost 796 km2 between 1990 and 1992 and another 564 km2 between 1992 and 1995 armadas of tabular icebergs were visible in front of this shelf in the ers images these two ice shelves mark the southern most documented conspicuous retreat of ice shelf margins

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

graphic correlation in frontier petroleum provinces application to upper paleozoic sections in the tarim basin western china when they were graphically correlated against a composite standard database paleontologic data sets from the carboniferous and lower permian of the western tarim basin revealed a punctuated stratigraphic succession in which most of geologic time is contained within regional hiatuses up to 15 m y duration these hiatuses occur beneath rock packages of late bashkirian middle moscovian late moscovian early kasimovian late gzhelian early asselian and early sakmarian artinskian ages this interpretation differs from other views that hold that permian carboniferous deposition in the tarim basin was continuous or nearly continuous with only minor breaks the results suggest that late paleozoic sedimentation in the tarim basin was controlled primarily by local processes not by third order global sea level cycles 1 3 m y duration the graphic correlation technique is capable of superior biostratigraphic resolution because it uses the ranges of all fossils within a data set not just guide fossils or those associated with zonal definitions moreover a composite standard that is linearly calibrated to geologic time makes possible inferences regarding rates of rock accumulation within stratigraphic sequences and the durations of sequence bounding hiatuses the resulting chronostratigraphic framework enables and constrains sequence stratigraphic and seismic stratigraphic interpretations

cenozoic deformation of the tarim basin and surrounding ranges xinjiang china a regional overview abstract with its central position between the tibetan plateau and the tian shan range the tarim basin is a key element of the cenozoic asian orogenic system however a comprehensive regional study and more particularly the quantification of shortening through this basin and its margins are still needed to understand its role in the cenozoic deformation of asia from a compilation of previous works together with an extensive dataset of satellite field seismic and well data we provide a tectonic map of the cenozoic structures and four balanced geological transects of the tarim basin and its surrounding ranges based on this map and these cross sections we characterize the cenozoic deformation of the original proterozoic tarim block from structural restorations and crustal budgets we also quantify the compressive component of this deformation most of the cenozoic compressive deformation from 94 to 100 is concentrated in the ranges along the block margins to the west up to 78 23 km and 54 24 18 km of crustal shortening are accommodated across the compressive western kunlun and southwestern tian shan ranges while to the east up to 38 6 18 km and 15 20 15 km are accommodated across the transpressive altyn tagh and southeastern tian shan ranges a non negligible amount of compressive deformation up to 6 is also accommodated within the tarim basin by large basement cored uplifts with a vergence synthetic to the deformation of the tibetan plateau edge to the west the bachu uplift absorbs 5 km of the total crustal shortening of the western kunlun thrust system while to the south the tanan uplift accumulates 0 6 km of the altyn tagh strike slip system structural inheritance has a major influence on the cenozoic deformation since 33 3 to 100 of the total shortening is accommodated by reactivated basement structures inherited from the protero paleozoic history of the tarim block finally we argue that the basement cored uplifts in the centre of the basin imply a deformation transfer from the tibetan plateau to the tian shan above a deep crustal decollement decoupling the deforming crust from an underlying rigid mantle

continental growth of northwest china the northwest corner of china is the most interior part of central asia and includes parts of the siberian tarim and kazakhstan plates where the junggar and tarim basins are separated by the east west trending tianshan range a preliminary terrane map divides the area into thirteen separate areas which are classified into four types l continental 2 oceanic crust 3 island arc 4 composite the boundaries for these terranes are faults that have been previously defined either by geologic mapping or holocene activity passive consolidation of the southern margin of paleo asia is marked by accretion and subduction of the paleo tethys oceanic basins and by development of volcanic arcs paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the permian or later the stratigraphic record reveals development of intracontinental basins in the late carboniferous followed by the pan asian thermal event that gave rise to widespread intrusion of a type granites of late paleozoic age the frontal collision of india along the southern border of asia in the paleocene reactivated nearly all of the older major strike slip and thrust faults formed during the late paleozoic consolidation of paleo asia the complex nature of the continental growth of central asia has produced and destroyed many varieties of sutures and reconstruction of the original plate and terrane configurations therefore is enigmatic

palaeozoic collisional tectonics and magmatism of the chinese tien shan central asia abstract the chinese tien shan range is a palaeozoic orogenic belt which contains two collision zones the older southern collision accreted a north facing passive continental margin on the north side of the tarim block to an active continental margin on the south side of an elongate continental tract the central tien shan collision occurred along the qinbulak qawabulak fault southern tien shan suture the time of the collision is poorly constrained but was probably in in the late devonian early carboniferous we propose this age because of a major disconformity at this time along the north side of the tarim block and because the youshugou ophiolite is imbricated with middle devonian sediments a younger probably late carboniferous early permian collision along the north tien shan fault northern tien shan suture accreted the northern side of the central tien shan to an island arc which lay to its north the north tien shan arc this collision is bracketed by the middle carboniferous termination of arc magmatism and the appearance of late carboniferous or early permian elastics in a foreland basin developed over the extinct arc thrust sheets generated by the collision are proposed as the tectonic load responsible for the subsidence of this basin post collisional but palaeozoic dextral shear occurred along the northern suture zone this was accompanied by the intrusion of basic and acidic magmas in the central tien shan late palaeozoic basic igneous rocks from all three lithospheric blocks represented in the tien shan possess chemical characteristics associated with generation in supra subduction zone environments even though many post date one or both collisions rocks from each block also possess distinctive trace element chemistries which supports the three fold structural division of the orogenic belt it is unclear whether the chemical differences represent different source characteristics or are due to different episodes of magmatism being juxtaposed by later dextral strike slip fault motions because the southern collision zone in the tien shan is the older of the two the tarim block sensu stricto collided not with the eurasian landmass but with a continental block which was itself separated from eurasia by at least one ocean the destruction of this ocean in late carboniferous early permian times represented the final elimination of all oceanic basins from this part of central asia

late paleozoic depositional history of the tarim basin northwest china an integration of biostratigraphic and lithostratigraphic constraints this study provides the first detailed lithostratigraphic and biostratigraphic constraints for improving stratigraphic resolution for hydrocarbon prospecting and exploration in the tarim basin a total of 49 stratigraphic units 38 formations and 11 members ranging in age from the latest devonian to permian are reviewed or redefined in terms of nomenclatures lithology age constraints and lateral distributions based on the detailed field works or newly published data of these the piqiang formation new formation is proposed to include the reefal carbonates of asselian sakmarian age from the northern tarim the subsurface upper paleozoic stratigraphic framework of the desert areas of the basin is also established for the first time the high resolution basinwide stratigraphic correlations reveal that the sedimentation of the basin in the late paleozoic was extremely uneven of these the famennian to changhsingian successions are completely recorded in the southwestern margin areas of the basin here five eustatic sedimentary cycles are well recognizable suggesting the sedimentation was more eustatically controlled and little affected by local tectonism the late paleozoic successions of both kalpin and taklimakan regions are commonly interrupted by major hiatuses at various horizons suggesting that the sedimentation was apparently modified by local tectonism of these the northward movement of the tarim block and its subsequent collision with the yili microcontinent part of the kazakhstan plate may be principally accountable for the discrepancy in the sedimentation of the various regions in the basin in the late paleozoic

geochemical characteristics and origin of natural gas in tarim basin china the tarim basin located in northwest china is one of the largest basins in the world that has not been well explored in recent years the large scale of petroleum exploration in the basin has led to the discovery of a series of oil and gas fields with an approximate 1 1 ratio of oil to gas resource this means that the natural gas resource is very important for the hydrocarbon resource in the tarim basin in this basin most of the discovered gases are condensate associated gas and oil associated gas research on chemical components and isotope composition of carbon and hydrogen of natural gases from the tarim basin shows that all discovered gases in this basin are thermogenic with respect to source organic matter there are two types of gases 1 oil type gas generated from sinian to lower paleozoic marine source rocks with the sapropelic organic matter with 44 5 to 33 8o oo of d13c1 42 0 to 28 1o oo of d13c2 35 4 to 28 4o oo of d13c3 and heavier than 200o oo of dd1 and 2 coal type gas generated from mesozoic terrestrial source rocks with the humic organic matter with 40 5 to 33 1o oo of d13c1 29 7 to 21 3o oo of d13c2 26 3 to 20 3o oo of d13c3 and lighter than 200o oo of dd1

final amalgamation of the central asian orogenic belt in ne china paleo asian ocean closure versus paleo pacific plate subduction a review of the evidence abstract the central asian orogenic belt caob evolved through complex closure of the paleo asian ocean from the neoproterozoic to the late phanerozoic this caused the chinese cratons to collide with eurasia and led to the formation of the world s largest phanerozoic orogenic belt ocean closure commenced in the west and was completed in the east near changchun closure of the paleo asian ocean in ne china was along the solonker xar moron changchun yanji suture and this was likely completed in the late permian although associated activity continued into the triassic there was an overlap in the latest permian early triassic between terminal activity associated with paleo asian ocean closure and the onset of tectonism associated with subduction of the paleo pacific plate this switch in geodynamic setting occurred at 260 250 ma and is reflected by a relaxing of north south directed compression and the onset of east west directed processes related to paleo pacific subduction by the early jurassic events associated with the westward advance of the paleo pacific plate dominated leading to extensive development of i type granites as far inland as the great xing an range from 140 ma the paleo pacific plate retreated eastward resulting in an extensional setting in the early cretaceous the effects of which were enhanced by regional thinning of the lithosphere commonly attributed to delamination throughout this period the eastern asian margin was tectonically complex the north south oriented jiamusi khanka bureya block was rifted away from the eastern margin of the caob in the late triassic but was then re united in the jurassic by westward advancing subduction that affected both the western and eastern margins of the block accretionary complexes continued to evolve in the cretaceous along the whole eastern margin of asia with final accretion of the nadanhada terrane part of the sikhote alin accretionary terrane with the caob at 130 ma followed by the emplacement of s type granites

new insights into the formation mechanism of high hydrogen sulfide bearing gas condensates case study of lower ordovician dolomite reservoirs in the tazhong uplift tarim basin huge high gas oil ratio hydrogen sulfide h2s bearing gas condensate accumulations were recently discovered in the ordovician carbonate reservoirs of the tazhong uplift in the tarim basin northwest china distinct differences exist between the eastern and western condensates in terms of chemical and isotopic compositions condensates from the western part of the uplift were characterized by high dibenzothiophenes generally 500 g g a high h2s concentration 7 vol vol and relatively depleted 13c methane 13c1 55 5 to 36 the h2s concentration in the tazhong gas condensates shows a positive correlation to mg2 concentration in the formation water formation water in lower ordovician cambrian strata in the tazhong uplift is rich in mg2 which facilitates the thermochemical sulfate reduction tsr of sulfate contact ion pairs cips to produce h2s and dibenzothiophenes a detailed comparison of the chemical compositions of the formation waters in different strata indicates that a high h2s concentration in the tazhong gas condensates originates from the tsr of sulfate cips in the lower ordovician cambrian strata where a primary oil accumulation may have existed the concentrations of 3 and 4 methyldiamantanes in the western condensates 80 to 150 g g are relatively lower than those from the eastern part of the uplift also the 13c1 in the western h2s bearing gas condensates was more negative and the 13c2 13c1 value was larger than that from typical tsr altered gases these features indicate that the western tazhong samples had just entered the initial stage of tsr according to the pressure volume temperature pvt phase diagram the lower paleozoic section was quickly buried after the tortonian high h2s hydrocarbon inclusions formed during the last 10 m y when paleotemperatures reached 140 c 284 f because the reaction rate of the sulfate cips oxidation was relatively slower than that of h2s autocatalysis during the entire tsr process advanced tsr has not been accomplished yet it is also inferred that the tortonian was the key period for accumulation of secondary h2s bearing gas condensates resulting from abundant gas washing along deep fractures and charging in the early reservoirs an increased aromaticity parameter toluene n heptane and an increased fractionation index from east to west indicate an intensified degree of gas washing different gas washing intensities in the eastern and western gas condensates led to diverse pvt states as well deep strata in the tazhong uplift were characterized by multiple charges and mixing coupled with periodic tsr leading to the occurrence of variable h2s bearing gas condensates

moho undulations beneath tibet from grace integrated gravity data summary knowledge of the variation of crustal thickness is essential in many applications such as forward dynamic modelling numerical heat flow calculations seismologic applications and geohistory reconstructions we present a 3 d model of the moho undulations over the entire tibetan plateau derived from gravity inversion the gravity field has been obtained by using the gravity recovery and climate experiment grace potential field development which has been integrated with terrestrial data and is presently the best available in the studied area for the effective use of the global geopotential model that has no height information of observation stations upward continuation is applied the moho model is characterized by a sequence of troughs and ridges with a semi regular pattern which could reflect the continent continent collision between the indian and eurasian plates the three deep moho belts troughs and shallow moho belts ridges between them are clearly found to have an e w directional trend parallel to the border of the plateau and tectonic lines while variation of the directionality is observed in central to southeast tibet to describe the distinctive shape of the moho troughs beneath tibet we introduce the term moho ranges the most interesting aspects of the moho ranges are 1 that they run in parallel with the border and tectonic sutures of the plateau 2 that the distances between ranges are found at regular distances of about 330 km except in northeast tibet and 3 that the splitting of the ranges into two branches is found as the distance between them is increasing from our study we conclude that the distinctive undulations of the tibetan moho have been formed by buckling in a compressional environment superimposed on the regional increase in crustal thickness according to our analysis the grace satelliteonly data turns out to have good enough resolution for being used to determine the very deep moho beneath tibet our moho model is the first one that covers the entire plateau

a middle ordovician darriwilian calathium reef complex on the carbonate ramp of the northwestern tarim block northwest china a sedimentological approach this study was supported by national natural science foundation of china 41072002 xdb10010503 and 41521061

thermochemical sulphate reduction in cambro ordovician carbonates in central tarim h2s and co2 are found in elevated concentrations in palaeozoic reservoirs in the tarim basin in china we have carried out analyses on gas petroleum mineral cement and bulk rock compositions and isotope ratios together with petrography and fluid inclusion to assess the origin of the h2s a deep crustal e g volcanic origin of the h2s and co2 is unlikely since the inert gases n2 and he have isotope ratios totally uncharacteristic of this source organic sources are also unlikely since the source rock has low a sulphur content and the sulphur isotope ratio of the petroleum correlates positively with the sulphur content the opposite of what would be anticipated from petroleum derived h2s bacterial sulphate reduction is unlikely because temperatures are too high for bacteria to have survived thermochemical sulphate reduction of petroleum fluids by anhydrite in lower ordovician and cambrian carbonate reservoirs is the most likely source of both the h2s and the co2 causing isotopically characteristic pyrite co2 gas and calcite cement h2s and possibly co2 migrated into silurian sandstone reservoirs by cross formational flow the h2s with the same sulphur isotope ratio as ordovician anhydrite was partially lost from the fluid phase by extensive growth of late diagenetic pyrite similarly the co2 was partially lost from the fluid phase by precipitation of late diagenetic calcite the h2s that resulted from tsr underwent reaction with the remaining petroleum resulting in locally elevated organic sulphur concentrations in the petroleum and the progressive adoption of the ordovician anhydrite sulphur isotope ratio

genetic origin of sour gas condensates in the paleozoic dolomite reservoirs of the tazhong uplift tarim basin abstract twenty gas condensates six oils and their associated formation water from the tazhong uplift in the tarim basin nw china were characterized for their molecular and isotopic compositions and water chemistry to elucidate the origins of the sour condensates thermochemical sulfate reduction tsr is the main secondary alteration process relevant to the generation of sour gas condensates those condensates are slightly heavier than regular condensates with a wide range of physical property and chemical composition variations the hydrogen sulfide h 2 s concentrations in gas phase show a strong positive correlation to gas oil ratio organosulfur compound osc concentrations in the liquid phase while methane isotopic values are mainly controlled by thermal maturity wet gas components show unusual 13 c enrichment at a low degree of thermal cracking geochemical anomalies occur mainly in the lower ordovician yingshan fm where more h 2 s has been discovered while the upper ordovician lianglitage fm shows less irregularity and h 2 s concentration is much lower generation of sour gas condensate is most likely caused by tsr alteration which could oxidize liquid hydrocarbons and form a large quantity of oscs isotopic enrichment of 34 s in formation water sulfate and elevated osc concentrations provide supplemental evidence of tsr alteration both burial history reconstructions based on fluid inclusion analysis and pvt simulation indicate that in situ tsr reactions mainly occurred around last 10 ma during the late himalayan orogeny and overall tsr extent is relatively low in the tazhong uplift

paleozoic oil source rock correlations in the tarim basin nw china we studied a suite of 40 oils and extracts of purported source rocks from the tarim basin in nw china the main group of oils comes from tazhong and tabei wells which sample the largest known petroleum accumulations in the basin these oils can be statistically correlated with extracts of ordovician rocks based upon high relative concentrations of 24 isopropylcholestanes and low relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes in contrast extracts from cambrian rocks have low relative concentrations of 24 isopropylcholestanes with high relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes although some tarim basin cambrian rocks yield high total organic carbon contents we see little evidence in the analyzed oil samples to suggest that they came from cambrian source rocks

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

ophiolites of the kunlun mountains china and their tectonic implications abstract three ophiolite belts ranging in age from cambrian to triassic provide valuable data on the tectonic evolution of the kunlun mountains which lie along the northern margin of the tibetan plateau all of the ophiolites contain dismembered but nearly complete assemblages of peridotite mafic and ultramafic cumulates pillow and massive lavas and radiolarian cherts 1 the oldest belt contains ophiolites of cambrian age but the initial spreading of the ocean basin most likely began in the late proterozoic these ophiolites outcrop in the central part of the eastern kunlun extend for at least a few hundred kilometers and are believed to reflect a small ocean basin closure of this ocean led the accretion of south kunlun block to the north kunlun block and tarim craton ophiolitic lavas in this belt have island are affinities 2 a second belt of early carboniferous ophiolites extends nearly 600 km along the northern margin of the western kunlun lavas in this belt are basalt basaltic andesite and andesite all of which have compositions characteristic of volcanic arcs this ocean basin possibly developed on the basis of the early paleozoic oceanic basin closure of this ocean basin by southward subduction in the early permian produced a suite of calc alkaline volcanic rocks in what is now the central part of the western kunlun 3 the third belt extends nearly 1200 km along the southern margin of the eastern kunlun and contains numerous ophiolites of early permian to middle triassic age these ophiolites are highly tectonized containing volcanic rocks with the geochemical characteristics of mid ocean ridges oceanic islands and volcanic arcs this belt is tentatively interpreted as the suture zone between gondwana and eurasia

closing history of the southern tianshan oceanic basin western china an oblique collisional orogeny abstract the tianshan tien shan range is an important paleozoic collisional orogenic belt and the key to understand the central asia tectonic evolution this paper integrates our research results with the existing chinese and international literature on sedimentology geochemistry isotopic geochronology paleontonology and paleomagnetism of the tianshan and tarim regions to propose that the oblique collision may have played an important role in the late paleozoic closing of the southern tianshan oceanic basin as a result of the sinian latest proterozoic younger than 800 ma continental extension and rifting process the tarim and yili blocks separated from their parent continent in the late cambrian ordovician the southern tianshan oceanic crusts between the two blocks subducted northward beneath the southern margin of the yili block in the silurian during the devonian early carboniferous the tarim block rapidly drifted to the north and rotated about 46 clockwise this process induced the collision of the yili micro continent with the eastern segment present geographical position of the tarim continent in the late devonian and the southern tianshan oceanic crust evolved to be a west facing remnant oceanic basin during the late carboniferous early permian the tarim block located within an almost constant latitude range rotated about 26 clockwise with respect to the yili micro continent which ultimately closed the remnant oceanic basin in a scissors like manner from east to west and completed the tarim yili collision subsequent a type subduction of the tarim continental crust and lithosphere scale sinistral shearing generated a magmatic arc on the southern margin of the tarim yili suture zone the late permian early triassic clastics deposited in a peripheral foreland basin developed above the arc

an apparent polar wander path from the tarim block china abstract the apparent polar wander apw path from the tarim block consists of devonian 16 n 165 e a95 4 late carboniferous 41 n 160 e a95 4 permian 61 n 177 e a95 9 early triassic 69 n 183 e a95 11 and jurassic cretaceous 65 n 214 e a95 6 poles on the basis of this apw path we conclude that tarim rode on a plate subducting under the kazakhstan plate between devonian and permian times by the end of the permian subduction had almost finished early triassic poles from tarim siberia north china and south china are discordant indicating post early triassic relative motions among them cretaceous paleomagnetic poles from tarim north china and south china however are consistent suggesting that china has been a coherent tectonic unit since cretaceous time the shape of the apw path from tarim is similar to that of siberia except that tarim s apw path is systematically displaced to the east a 26 clockwise rotation of tarim s apw path about the euler pole 60 n and 14 e reconciles these two apw paths tarim has moved northeastward some 2000 km relative to a fixed siberia since the cretaceous this northeastward motion of tarim with respect to siberia agrees well with the overall cenozoic tectonic style of asia most of southern china has been pushed eastward to give way to the penetrating indian continent east west and northeast trending left lateral strike slip faults north of the tarim block have been documented however the exact amounts of displacement along these faults are not well known using paleomagnetic data from tarim we will also discuss the tectonic evolution of terranes in central asia and the amount of continental shortening in the tibetan plateau

planation surfaces of the tian shan range central asia insight on several 100 million years of topographic evolution abstract in central asia numerous fragments of planation surfaces are visible within the present day topography however their precise timing of formations is still poorly constrained and it is not clear if they are remnants of a single extensive planation surface or if they represent different planation episodes by reconstructing the landscape evolution of the tian shan region and by analyzing the relations between the planation surfaces preserved within the eastern tarim basin and the sedimentary record we demonstrate that the numerous erosional surfaces preserved within the tian shan range represent different episodes of surfaces genesis these erosion events span from the late paleozoic to the early cenozoic the widespread preservation of large fragments of these surfaces within the tian shan range implies that this region did not undergo strong relief building during most of its mesozoic evolution but was dominated by plains associated to small hills along episodically active discrete tectonic structures finally the preservation of these surfaces within the active tian shan range implies a long term strong non equilibrium state of the topography during its cenozoic evolution this was probably promoted by the arid to semi arid climate prevailing since the late paleogene onset of relief building

structural features of northern tarim basin implications for regional tectonics and petroleum traps the rhombus shaped tarim basin in northwestern china is controlled mainly by two left lateral strike slip systems the northeast trending altun fault zone along its southeastern side and the northeast trending aheqi fault zone along its northwestern side in this paper we discuss the northern tarim basin s structural features which include three main tectonic units the kalpin uplift the kuqa depression and the north tarim uplift along the northern margin of the tarim basin structural mapping in the kalpin uplift shows that a series of imbricated thrust sheets have been overprinted by strike slip faulting the amount of strike slip displacement is estimated to be 148 km by restoration of strike slip structures in the uplift the kuqa depression is a mesozoic cenozoic foredeep depression with well developed flat ramp structures and fault related folds the baicheng basin a quaternary pull apart basin developed at the center of the kuqa depression subsurface structures in the north tarim uplift can be divided into the mesozoic cenozoic and the paleozoic lithotectonic sequences in seismic profiles the paleozoic litho tectonic sequence exhibits the interference of earlier left lateral and later right lateral strike slip structures many normal faults in the mesozoic cenozoic litho tectonic sequence form the negative flower structures in the north tarim uplift these structures commonly directly overlie the positive flower structures in the paleozoic litho tectonic sequence the interference regions of the northwest trending and northeast trending folds in the paleozoic tectonic sequence have been identified to have the best trap structures our structural analysis indicates that the tarim basin is a transpressional foreland basin rejuvenated during the cenozoic

tarim underthrust beneath western kunlun evidence from wide angle seismic sounding abstract this paper describes the results of a wide angle seismic profile over 700 km long across the southern margin of the tarim basin a crustal structure that best fits the observed data that tests and verifies the earlier discovery that the crystalline basement dips southward from the area of the petroleum industry seismic reflection profiling and geological investigation is presented the profile also reveals that the moho dips southward beneath the southern tarim at an angle in concordance to that of the crystalline basement this result is thought to be the first evidence for the underthrusting of the tarim crust beneath the western kunlun additional evidence of underthrusting is that the relatively weak western kunlun crust has contracted and expressed by a lower crust which is more than 20 km thick with an uplift of the kunlun basement accompanied by northward directed thrusts

basal melting and freezing under the amery ice shelf east antarctica the basal melting and freezing rates under the amery ice shelf east antarctica are evaluated and their spatial distributions mapped ice velocity surface elevation and accumulation rate datasets are employed in the analysis along with a column averaged ice density model our analysis shows that the total area of basal melting is 34 700 km 2 with a total annual melt of 62 5 9 3 gt and an average melting rate of 1 8 0 3 m a 1 basal freezing mainly occurs in the northwestern part of the ice shelf over a total area of 26 100 km 2 and with a maximum freezing rate of 2 4 0 4 m a 1 the total marine ice that accretes to the ice shelf base is estimated to be 16 2 2 4 gt a 1 using a redefined grounding line and geometry of the amery ice shelf we estimate the net melt over the ice shelf base is about 46 4 6 9 gt a 1 which is higher than previous modeling and oceanographic estimates net basal melting accounts for about half of the total ice shelf mass loss with the rest being from iceberg discharge our basal melting and freezing distribution map provides a scientific basis for quantitative analysis of ice ocean interaction at the ice shelf ocean interface

paleozoic tectonic evolution of the tianshan orogen northwestern china abstract the chinese tianshan orogenic belt which extends west east for about 1500 km is one of the most important paleozoic orogenic belts in central asia it includes parts of the tarim yili central tianshan and junggar plates which are microcontinental blocks with precambrian basements and meso cenozoic depositional covers the tarim plate is separated from the yili central tianshan plate by the southern central tianshan suture early carboniferous ophiolitic melanges and blueschists are widespread in this suture and are believed to be produced by the collision between a passive continental margin on the north side of the tarim plate and an active continental margin on the south side of the yili central tianshan plate the collision occurred at the end of early carboniferous the yili central tianshan and the junggar plates are separated by the northern central tianshan suture also considered as an early carboniferous collisional zone along which the middle ordovician ophiolitic melanges blueschists and late devonian early carboniferous ophiolites are exposed in early paleozoic times the subduction of the paleo junggar ocean took place in an active margin on the north side of the yili central tianshan plate along the northern central tianshan suture at the end of early carboniferous the north side of the yili central tianshan plate collided with the north tianshan arc along this suture the paleo oceanic crust in the tianshan and adjacent region was entirely consumed at the end of early carboniferous meanwhile the tarim yili central tianshan and junggar plates were accreted to eurasia epicontinental sediments were then deposited throughout the tianshan region during the middle late carboniferous times in the early permian tianshan began to uplift with accompanying volcanic eruption and granitic intrusion the uplift was accelerated in the late permian and continental molasse was extensively deposited

oceanic controls on the mass balance of wilkins ice shelf antarctica 0 8 m a 1 driven by a mean basal melt rate of wb 1 3 0 4 m a 1 interannual variability was large associated with changes in both surface mass accumulation and wb basal melt rate declined significantly around 2000 from 1 8 0 4 m a 1 for 1992 2000 to 0 75 0 55 m a 1 for 2001 2008 the latter value corresponding to approximately steady state ice shelf mass observations of ocean temperature t obtained during 2007 2009 by instrumented seals reveal a cold deep halo of winter water ww t 1 6 c surrounding wis the base of the ww in the halo is 170 m approximately the mean ice draft for wis we hypothesize that the transition in wb in 2000 was caused by a small perturbation 10 20 m in the relative depths of the ice base and the bottom of the ww layer in the halo we conclude that basal melting of thin ice shelves like wis is very sensitive to upper ocean and coastal processes that act on shorter time and space scales than those affecting basal melting of thicker west antarctic ice shelves such as george vi and pine island glacier

a synthesis of remote sensing data on wilkins ice shelf antarctica wilkins ice shelf has an area of 16000 km2 and lies off the west coast of the antarctic peninsula bounded by alexander latady charcot and rothschild islands several ice shelves including wilkins exist close to a climatic limit of viability the recent disintegration of the neighbouring wordie ice shelf has been linked to atmopsheric warming observed on the antarctic peninsula the limit of ice shelf viability thus appears to have migrated south should this continue the question arises how long will wilkins ice shelf survive compared with the other ice shelves on the antarctic peninsula few surface glaciological data have been collected on wilkins ice shelf we compare contrast and combine a variety of remotely sensed data the recently declassified geosat geodetic mission altimetry landsat mss and tm imagery and radio echo sounding data res to study its structure and mass balance regime we find that this shelf has an unusual mass balance regime and relies heavily for sustenance on in situ accumulation its response to a continued atmospheric warming may be significantly different from that of wordie ice shelf wordie ice shelf was fed by several dynamic outlet glaciers which accelerated the disintegration process when the ice shelf fractured wilkins ice shelf by contrast is almost stagnant and is expected to respond by normal calving at the ice front changes in the accumulation rate or basal melt rate may however dominate any dynamic effect over the last two decades the ice front positions have remained stable

carboniferous triassic subduction and accretion in the western kunlun china implications for the collisional and accretionary tectonics of the northern tibetan plateau a newly defined 250 km by 500 km carboniferous triassic subduction accretion complex the mazar accretionary prism in the western kunlun comprises two subduction complexes and a forearc basin succession 1 the bazar dara subduction complex contains imbricated blocks of sandstone arenite limestone and metavolcanic rocks in a matrix of weakly metamorphosed triassic deep sea turbidites the metavolcanic rocks include basalt diabase spilite and andesitic porphyry trace element geochemistry shows that pillow and amygdaloidal basalts are oceanic island tholeiites this zone has ordovician to permian fossils and is situated on the older more highly deformed and metamorphosed side of the prism adjacent to the sailiyak magmatic arc 2 the heweitan subduction complex is composed of blocks of limestone turbidite and radiolarite in a slate phyllite matrix intercalated with calc alkalic volcanic rocks this complex has permian to triassic fossils and is situated on the younger less deformed and metamorphosed side of the prism adjacent to the suture zone 3 the qitai forearc basins are infilled with turbidites late triassic intercalated with carbonates these rocks overlie the accretionary prism the accretion related structure is dominated by large scale northeast dipping thrusts and subvertical cleavage stitched by 215 190 ma granites there is an overall decrease in metamorphic grade and deformation intensity from the arc to the suture zone across the bazar dara and heweitan subduction complexes the mazar accretionary prism formed by subduction accretion processes during closure of the paleotethyan ocean and the final docking of the gondwanan karakoram qiangtang block to the cathaysian eurasian kunlun block

ediacaran early ordovician and early silurian arcs in the south tianshan orogen of kyrgyzstan abstract the oldest magmatic rocks from the south tianshan orogen of kyrgyzstan sts are important for better understanding of the neoproterozoic and early palaeozoic evolution of the southwestern central asian orogenic belt bulk rock major and trace element and sm nd isotopic composition and zircon u pb ages of granitoids from melange blocks reveal two previously unknown episodes of arc magmatism in the sts orogen of kyrgyzstan namely the ediacaran ca 624 ma and early ordovician ca 472 ma episodes moderately positive nd t value of 5 8 of the ediacaran granodiorite indicates a mainly juvenile source for this rock negative nd t value of 9 1 for the early ordovician granodiorite indicates melting of the predominantly precambrian crustal material the latter is also supported by the inherited zircon cores with an age range of 1 04 2 7 ga the geochemical signature of the silurian late llandovery and wenlock basalts suggests formation in arc settings arc related origin of the ediacaran granodiorite suggests that mature oceanic basin with subduction system existed in the western sts since the late neoproterozoic the arc also evolved in the ordovician and silurian and was inactive in the middle cambrian to the earliest ordovician ediacaran granodiorite old zircon cores and negative nd t values of the ordovician granodiorite suggest the existence of precambrian microcontinents in the kyrgyz sts these crustal fragments were likely rifted off the tarim and or karakum tajik microcontinents where the rocks with similar ages occur in the palaeozoic they traveled north and were incorporated in the sts orogen in the late carboniferous

carbonaceous microstructures from sedimentary laminated chert within the 3 46 ga apex basalt chinaman creek locality pilbara western australia abstract hydrothermal black chert veins intruding the 3 46 ga apex basalt contain some of earth s oldest microfossil like objects whose biogenicity has been questioned whilst these black chert veins have been studied in great detail relatively little is known about the stratiform seafloor sedimentary cherts that are conformably interbedded with volcanic rocks of the apex basalt herein we document and assess the biogenicity of carbonaceous microstructures present in the lowermost of the stratiform chert units informally known as the apex chert at the chinaman creek locality in the marble bar greenstone belt pilbara craton western australia carbonaceous material mostly occurs within clotted grey black cherts and microgranular grainstone like cherts within the stratiform unit the latter being the major focus of this study in the clotted cherts carbon occurs as lobate fluffy grains rare compressed flakes and as a grain boundary phase around spherulitic silica there is no morphological evidence to support the biogenicity of these microstructures in contrast the microgranular chert contains fluffy and flaky carbonaceous grains plus laminated grains comprising multiple non isopachous wrinkled carbonaceous laminae with noted thickening towards some ridge crests as determined by confocal laser scanning microscopy roll up structures provide evidence of an initial plasticity interpreted to have formed via the tearing up and current induced plastic deformation of microbial mat fragments geochemical mapping using laser raman micro spectroscopy and nanosims respectively demonstrates the antiquity of the carbon and reveals a close correlation between carbon nitrogen and sometimes sulphur concentrated within dark brown to black laminae adjacent to microgranular zones are zones of more persistent carbonaceous undulose filament like laminae that entrain relict sediment grains these microstructures are directly comparable to a sub type of microbially induced sedimentary structure miss widely reported from younger siliciclastic sediments colonised by microbial biofilms the morphology and chemical composition of both the non isopachous laminated grains and the filament like laminae are consistent with a biological interpretation suggesting microscopic miss were present in the microgranular stratiform apex chert however the fact that neither macroscopic miss nor bona fide microfossils have yet been reported from this unit coupled with the proximity of these structures to active hydrothermal vents potentially discharging hot carbon rich fluids urges caution in such an interpretation the chinaman creek apex chert investigated here is one of at least five sedimentary laminated cherts within the apex basalt these horizons are promising targets in the search for biological activity within a dominantly volcanic archaean environment

seismic image of the tarim basin and its collision with tibet a broadband seismic deployment in 1998 1999 in southwestern tarim provided data for imaging the crust and upper mantle across the contact between the tarim block and the tibetan plateau a profile composed of migrated teleseismic receiver functions clearly shows lateral structural changes the crust under the tarim basin is relatively simple the moho discontinuity is mapped at a depth of 42 km near the northern end of the array and dips gently toward the south to 50 km under the kunlun foreland the tarim basin appears to be rigid with little shortening farther to the south the imaging reveals a complex of reflectors in the lower crust and the upper mantle there are both north and south dipping upper mantle structures under the kunlun foreland and kunlun shan region we found the observations to be more consistent with a model of lithospheric collision in which the crust and the upper mantle on both sides interpenetrate and deform

windward and leeward margins of an upper ordovician carbonate platform in the central tarim uplift xinjiang northwestern china abstract in the central uplift of the tarim basin northwestern china the katian upper ordovician limestones of the lianglitag formation extend from outcrops in the bachu area to the subsurface in the tazhong oil field tzof area reefs and inner platform deposits are the dominant facies throughout the formation the reef composition illustrates a palaeoecologic gradient from microbial dominated buildups on the northwestern margin to metazoan dominated reefs on the eastern and southern margins of the platform between these areas no outcrops are present in the present study data including litho and biofacies logs and correlations from eight wells are presented six of them of the region between bachu and tazhong and two wells along the former platform margin from the tzof calcimicrobial carbonates are common in core from the inner platform part benthic biota documented here resembles that of the microbial mounds and bioclastic limestones in the bachu outcrop area and thus is considered as the eastward extension of this realm however metazoan dominated boundstones formed by corals stromatoporoids sponges together with calcareous algae are abundant along the southern platform margin and are similar in composition to the reefs of tzof in the easternmost part of the platform the palaeoecologic differentiation between microbial and metazoan dominated reefs suggests a strong environmental gradient from a well oxygenated windward eastern and southern side of the platform which favoured the open ocean and which was dominated by metazoan reefs and the inner platform as well as the northwestern leeward margin of the platform with warmer less oxygenated water which favoured the growth of microbial carbonates assuming the trade winds as cause for the contrasting facies on both sides of the platform a palaeo position of tarim south of the itcz seems probable because a position north of it would require a post ordovician clockwise rotation of tarim of about 90 which is possible but less probable

melting and freezing beneath filchner ronne ice shelf antarctica 1 we use remote sensing data sets to evaluate the spatial distribution of melt beneath the filchner ronne ice shelf fris the net melt rate of 83 4 24 8 gtons yr is 2 5 5 times lower than previous glaciological estimates but is similar to existing oceanographic estimates the spatial distribution however differs significantly from standard conceptual and numerical models in which most melt occurs along the grounding lines our results suggest most grounding line melt is refrozen while the dominant ice shelf water isw source is melting near the ice shelf front probably associated with tidal action this suggests that changes in ice shelf extent can impact isw production rates in the weddell sea

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

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

the tazhong hybrid petroleum system tarim basin china abstract the tazhong petroleum system is geographically located in the central tarim basin including the tazhong uplift the north slope and the southern area of the manjiaer depression the total thickness of early palaeozoic to cenozoic sediments reaches 6500 9500 m the manjiaer depression and the north slope are the two major petroleum source areas with three sets of source rocks cambrian black shales and ordovician dark carbonates of the manjiaer depression and ordovician argillaceous limestones of the north slope there are three sets of reservoir cap rock combinations in this petroleum system the main periods for oil generation from these source rocks occurred during the middle silurian to early devonian late carboniferous to early triassic and tertiary there were three corresponding phases of petroleum migration well developed thrust faults and unconformity surfaces in this area provided the main pathways for petroleum migration as some of the faults cut through all the lower palaeozoic strata the oil in any given reservoir rock may be actually a mixture of oils from different sources complicating the origin and properties of the hydrocarbons in the reservoir and forming a hybrid petroleum system the formation of a typical oil and gas pool in this petroleum system may be attributed to one or all of three petroleum events which were closely associated with the regional tectonics the first event occurred in the early palaeozoic tectonic cycle and the generated oil accumulated in lower silurian sandstone the second event occurred in the late palaeozoic tectonic cycle and formed light oil pools mainly in lower silurian and ordovician reservoirs the third event took place during the cenozoic tectonic cycle and formed normal crude oils the oil and gas generated from different sources in different phases may co exist with one another in a reservoir rock however the commercial oil and gas pools are related to the cenozoic and late palaeozoic events

the stratigraphic sedimentological and structural evolution of the southern margin of the kazakhstan continent in the tien shan range during the devonian to permian