contrasting nature of petroliferous mesozoic cenozoic basins in eastern and western china onshore petroliferous basins of mesozoic cenozoic age in china include two distinct geographic geotectonic groups eastern extensional rifted basins and western compressional orogenic basins eastern basins are faulted depressions and crustal sags that formed where incipient intracontinental rifting thinned the crust and developed tilted fault blocks and half grabens bounded by normal faults western basins are flexural downbows that were depressed under the tectonic load of adjacent thrust sheets associated with the folded mountain ranges of central asia source beds in both groups of basins are dominantly dark lacustrine mudstones of terrestrial facies associations and reservoirs are mainly fluviodeltaic sandstones hydrocarbon traps in the eastern basins include e tensional rollover anticlines compactional drape anticlines diapiric salt domes buried hill highs in the substratum and stratal pinch outs on the flanks of buried highs simple or faulted anticlinal traps are dominant in the western basins multiple reservoir horizons are characteristic of oil fields in both groups of basins orogenic compression which developed the western basins is attributed to the successive collision of microcontinents with the southern edge of the composite eurasian continental mass crustal extension which developed the eastern basins is attributed to incipient rifting within and behind magmatic arcs along the margin of the pacific ocean basin

an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

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

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

the turbulent structure and diurnal growth of the saharan atmospheric boundary layer the turbulent structure and growth of the remote saharan atmospheric boundary layer abl is described with in situ radiosonde and aircraft measurements and a large eddy simulation model a month of radiosonde data from june 2011 provides a mean profile of the midday saharan abl which is characterized by a well mixed convective boundary layer capped by a small temperature inversion 1k and a deep near neutral residual layer the boundary layer depth varies by up to 100 over horizontal distances of a few kilometers due to turbulent processes alone the distinctive vertical structure also leads to unique boundary layer processes such as detrainment of the warmest plumes across the weak temperature inversion which slows down the warming and growth of the convective boundary layer as the boundary layer grows overshooting plumes can also entrain freetropospheric air into the residual layer forming a second entrainment zone that acts to maintain the inversion above the convective boundary layer thus slowing down boundary layer growth further a single column model is unable to accurately reproduce the evolution of the saharan boundary layer highlighting the difficulty of representing such processes in large scale models these boundary layer processes are special to the sahara and possiblyhot dry desertenvironmentsingeneral andhaveimplicationsforthelarge scalestructureofthesaharan heat low the growth of the boundary layer influences the vertical redistribution of moisture and dust and the spatial coverage and duration of clouds with large scale dynamical and radiative implications

speculations on the mesozoic plate tectonic evolution of eastern china several orogenic belts transecting eastern china are the sites of former convergent plate margins although there have been varying views on the collisional framework of individual continental blocks styles of convergence at these zones and the timing of respective collisions a tectonic study of eastern china mongolia and the southern soviet far east indicates the collision of the south china block with a combined north china northeast china fold zone block in the late triassic early jurassic their collective suturing to eurasia in the late jurassic early cretaceous followed by the sikhote alin japan block in the mid to late cretaceous the evidence is as follows 1 a linear belt of late triassic early cretaceous granites and granodiorites trends east from the qinlingshan through the dabieshan to the huaiyang massif ophiolites flysch subduction zone melange a paired metamorphic belt indicating north dipping subduction and marine strata of carboniferous to late triassic age from the qinlingshan define the suture between the north and south china blocks 2 a sinuous belt of ultramafics blueschists silicic to intermediate magmatism and west and north vergent folds and thrusts trend from the west margin of the ordos basin through central inner mongolia and along the east great khingan range to the amur river coupled with a mid jurassic early creataceous unconformity a suturing of eastern chinese blocks to eurasia along this zone is suggested 3 a fold and thrust belt with ultramafics flysch blueschists and subduction zone melange along the ussuri river in northeast china indicates the suturing of the sikhote alin japan block to eurasia along a west dipping subduction zone in the mid to late cretaceous similarly a tectonic study of southern china and southeast asia has revealed a complex regional mosaic of suture bounded terrains which nucleated about the eastern western and southern margins of the yangtze craton during the late triassic and early jurassic the evidence is as follows 4 a north south trending belt of ophiolites blueschists calc alkaline volcanics and subduction zone melange including granites granodiorites and strongly deformed marine strata all of late triassic age exposed in the longmenshan of sichuan merge with the kekexilishan ophiolite zone into the ailaoshan tengtiaohe ophiolite and blueschist belt in central yunnan along which the songban ganzi complex and the shan thai malaya block join the craton and 5 a southeastern prolongation of the ailaoshan tengtiaohe belt bifurcates into the southeast trending konvoi zone of northern vietnam and the north south trending pak lay luang prabang zone of laos and eastern thailand zones of ophiolite calc alkaline volcanics and strong late triassic deformation they separate the indosinia and shan thai malaya blocks from the craton respectively these findings differ significantly from previous interpretations of a late paleozoic consolidation of south eastern asia as well as disputing the existence of a true pangea

some comments on two layer extensional models for the evolution of sedimentary basins simple extensional models that involve listric faulting in the brittle upper crust and plastic flow in the lower lithosphere have been shown to account for the subsidence history of various continental sedimentary basins and continental shelves in this paper we present structural evidence that extension in the continental lithosphere during rifting is not uniform we review evidence that the rifting process in major intracratonic rift basins is spasmodic rather than continuous that extension and subsidence within the rift during a tectonic phase is generally accompanied by uplift and erosion of the rift flanks that subcrustal heat input during rifting occurs over an area much broader than the rift proper and that there may be broad regional uplift before and or during rifting to explain the uplift of the flanks during rifting and their postrift subsidence we invoke two mechanisms subcrustal thinning by extension below the flanks and tilted major normal faults in the crust between graben and flanks the uplift and erosion of the flanks due to tilted faults probably do not significantly affect estimates of extension from subsidence analysis but uplift due to both sources can in certain cases be incorrectly attributed to regional uplift or doming we present a simplified analysis of the two layer extensional model for the elementary case in which extension is instantaneous and the crust is thinned by a different amount from the subcrustal lithosphere we provide a simple graphical method of data analysis to obtain the parameters that describe thinning of the crust and lithosphere during extension from the subsidence history application of this method to the central part of the pattani trough in the intracratonic gulf of thailand shows that extension and thinning of the lithosphere of a factor of 2 since late eocene can account for much of the subsidence history and the present day heat flow our analysis suggests that thinning of the crust in this area is 20 greater than thinning of the whole lithosphere assuming that none of the lithosphere is removed from the region of extension during rifting we show by simple geometric examples that a process of nonuniform extension implies that much greater thicknesses of sediment can be deposited in the center of a young basin than in the case of uniform extension of both crust and subcrustal lithosphere such an extensional process produces significant uplift of the flanks of the rift and as a result of erosion of the uplifted areas the effective cross sectional area of the basin can be increased by as much as 10 20 depending on the rate of erosion compared to the area that would have been created by a process of uniform extension finally we show that it may ultimately be possible to compute erosion rates from seismic cross sections of basins

lithospheric flexure and the evolution of sedimentary basins the sediments that have accumulated in sedimentary basins during geological time represent a load on the lithosphere that should respond by flexure simple elastic and viscoelastic maxwell plate models have been used to examine quantitatively the contribution of flexure to basin formation the models have been used to predict the stratigraphy and gravity anomalies associated with basins for different thermal and loading histories the predictions of the models have been compared with observed stratigraphy and free air gravity anomalies from interior and cratonic basins the best overall fit to the observations is for an elastic plate model in which the flexural strength of the lithosphere increases with age a similar model has recently been used successfully to explain observations from continental margin basins oceanic islands and seamounts and deep sea trench outer rise systems this model explains the increase in the overall width of basins during their evolution as well as the stratigraphy of the basin edges the apparent decrease in the widths of some basins through time can be explained by the model if sediment deposition is followed by erosion of the basin and its edges the models results suggest that the flexural properties of continental and oceanic lithosphere are generally similar and that flexure is an important factor to consider in backstripping studies in which the tectonic subsidence of a basin is isolated and stratigraphic studies in which relative changes of sea level are estimated

timing tectonic implications and genesis of gold mineralization in the xincheng gold deposit china c h o isotopes pyrite rb sr and zircon fission track thermochronometry abstract the xincheng gold deposit located at the northwestern edge of the jiaodong peninsula in the north china craton has a reserve of 96 t au and is among the largest in the jiaodong gold province here disseminated and stockwork style ores are hosted in mesozoic granitoids the mineralization and alteration are largely controlled by the regional jiaojia fault the c h o isotope values in the ores indicate that the ore forming fluids were derived mainly from magmatic sources new rb sr geochronological data on hydrothermal pyrite from the xincheng deposit presented in this study indicate that the main gold mineralization occurred between 126 ma and 122 ma the zircon fission track of convergent ages and decomposed divergent ages from the ores and altered rocks show four groups of ages 135 ma 124 ma 96 75 ma and 66 52 ma the 135 ma is related to the exhumation and cooling of the linglong granitoids the 124 ma is considered to represent the principal stage of gold mineralization and is consistent with the pyrite rb sr ages the younger ages of 96 75 ma and 66 52 ma resulted from subsequent annealing caused by later tectonic activity the timing of gold mineralization in the xincheng gold deposit broadly coincides with the switch in stress field in eastern china from extension to transpression resulting from the change in subduction direction of the pacific plate from ne sw to nw se and marked by extension related voluminous magmatism associated with the cretaceous giant igneous event in eastern china

plume related sedimentary basins in east asia during the cretaceous abstract many cretaceous sedimentary basins of various sizes occur in east asia which are classified into four geotectonic settings forearc intra arc back arc and intra continental basins among these intra arc and back arc basins are characterized by rifting and pull apart origins and intra continental basins by rifting related to large scale magmatism or plume the pull apart basins in southwest japan are closely related to plate subduction magmatism the continental region rift basins in the early cretaceous however seem to have no direct relation to subduction controlled magmatisms because almost no accretionary prism was developed along the continental margin at that time this means that plume related magmatism played an important role in the eastern part of the asian continent due to return flow effects from the 670 km thermal boundary layer such a plume magmatism explains systematically the origin and development of varieties of rift basins in east asia in cretaceous time

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

a mid mesozoic extension across central asia although relatively little is known about basin formation north of the himalayas recent stratigraphic studies of several sedimentary basins tarim dzhungaria tsaidam have demonstrated a common pattern of subsidence in post triassic times1 all these basins show rapid subsidence concurrent with the onset of himalayan orogenesis presumably reflecting both tectonic loading and increased sediment supply before that time however subsidence curves have the characteristic concave up shape of rifted margin sedimentary environments2 although data from these basins are not sufficiently detailed to justify a more thorough investigation the tadjik depression a sedimentary basin comprising the southwestern portion of the soviet republic of tadjikistan fig 1 contains a continuous and relatively well documented record of post jurassic sedimentation analysis of which suggests deposition in a rifted margin environment on crust thinned by 50

the north china basin an example of a cenozoic rifted intraplate basin the north china basin was a stable continental region that has undergone several distinct phases of rifting and subsidence during the mesozoic and cenozoic eras the last major phase featuring block faulting rapid subsidence and widespread calc alkaline basaltic volcanism began during early tertiary time this intraplate rifting appears to be the result of an approximately 30 extension and thinning of the lithosphere beneath the northeastern china by the late tertiary period active rifting had slowed and postrift thermal subsidence had begun this regional extension and subsidence resulted in the present day north china basin a large saucer shaped oil producing basin with thinner crust and lower upper mantle p and s wave velocities than the surrounding regions during the quaternary period however the subsidence rate increased in the north china basin the frequent occurrence of destructive earthquakes and observations of relatively high heat flow suggest that the quaternary tectonic activity differs from the late tertiary simple thermal subsidence pattern and may indicate a new phase of rifting

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

geologic evolution of petroliferous basins on continental shelf of china the coastline of southeastern china is about 18 000 km 11 200 mi in length and its aggregate continental shelf area within 200 m 660 ft water depth is well over 1 million km2 390 000 mi2 recent geophysical exploration and petroleum drilling records aid in understanding the geologic evolution of these petroliferous basins two types of tectonic basins are present on the continental shelf areas 1 bohai gulf south yellow sea and beibu gulf are intraplate polyphase rift depression basins and 2 east china sea mouth of the pearl river and the yingge sea are epicontinental rift depressions basins both types are believed to be of extensional origin the severe convergence of the indian plate with the eurasia plate produced east northeast s reading of the south china sea basin which resulted in two triple junctions on its northern margins the pacific plate was subducted by downthrust beneath the eurasia continental crust the extension mechanism could be the rising of an upper mantle plume to produce two weak north northeast trending fracture zones a series of intraplate and epicontinental rift depression basins was formed the depositional models and sea level variations of these basins have been interpreted from drilling records and seismic profiles they can be explained by the tectonoeustatic changes in sea level and cenozoic climatic changes in china

eastern asia and the western pacific timing and spatial distribution of rifting in china abstract a compilation of recognized rifts in china indicates that five distinct episodes of rifting have occurred these episodes occurred at approximately 2 3 ga 1 85 1 7 ga 1 0 0 7 ga 550 190 ma and 175 ma to present the timing and location of rifting has largely been a function of tectonic activity along the margins of the various chinese paleocontinents some of the oldest rocks in china are found in the sino korean and tarim cratons and most of the identified precambrian rifts are found within or on the margins of these cratons these cratons are viewed as the continental nucleus of china and fold belts and microcontinents have been accreted to this nucleus through time much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin especially in the paleozoic beginning in the middle mesozoic rifting commenced along the entire eastern margin of china extension occurred concomitantly with subduction in a backarc setting this is the dominant cenozoic extensional regime in china and is still active today to date few cenozoic rifts have been found in western china where most tectonism is probably a consequence of the collision between india and china but it seems likely that more rifts will be discovered in this area as it becomes better studied

types of cenozoic sedimentary basins of the east asia and pacific ocean junction area abstract a rather wide class of structures has been distinguished in marginal basins the marginal basins in the modern pacific can be classified based on the type of crust and their position relative to the structures of active continental margin sedimentary basins of the philippine sea east china sea yellow sea and bohai sea comprise oceanic and transitional crust and form trenches and back arc inter arc forearc and intra arc basins basins with continental crust consists of marginal continental shelf and intracontinental basins in the first type basins the crust thickness ranges from 4 2 to 24 km they are sea basins rather deep only partially filled with marine sediments with substantial volcaniclastics and lavas their basement is generally made up of volcanics in inter and intra arc basins of the group polymetallic sulphide ores have been found treches have favourable conditions for gas accumulation the second type of basin was fonmed at the expense of rifting of continental crust with a thickness of 28 44 km they are completely filled with alluvial deltaic and lacustrine sediments up to 11 km thick basins of this type are rich in oil and gas

junggar turfan and alakol basins as late permian to early triassic extensional structures in a sinistral shear zone in the altaid orogenic collage central asia the junggar turfan and alakol basins in northwestern china and kazakhstan formed as late permian to early triassic extensional structures in a broad sinistral shear zone between large strike slip faults that separate two main domains of the altaid orogenic collage this extension was in response to an inferred large l000 km sinistral motion of the east european craton with respect to the angaran craton during this time deformation associated with the formation of the basins was taken up in part by counter clockwise rotations of crustal blocks with respect to the altaid orogenic collage and to the angaran craton this event is the only important phase of extension in a region otherwise dominated by compressional tectonics throughout the phanerozoic the basement rocks of these basins formed by altaid subduction accretion through the latter half of the palaeozoic and the region was subsequently thrown into compression again during the mesozoic cimmeride and cenozoic alpide evolution

cretaceous paleogeography and paleoclimate and the setting of ski borehole sites in songliao basin northeast china article i nfo as a paradigm of greenhouse climate in earth s history the cretaceous provides significant rock records of global climate changes under conditions of greenhouse climate the songliao basin among the longest dura tion 85 90 m y of continental sedimentary basins provides an excellent opportunity to recover a nearly complete cretaceous terrestrial sedimentary record extensive lake deposits ten kilometers deep and cover ing an area of 260 000 km 2 of the songliao basin provide unique detailed records that can be tied to the glob al stratigraphic time scale thereby improving our understanding of the continental paleoclimate and ecological system the two coreholes at skis and skin sites were drilled into this basin and completed with a total length of 2485 89 m of recovered core that spanned the complete middle to upper cretaceous strata in the basin the unique geological setting of long term continuous subsidence within the largest cretaceous landmass in the world makes the cretaceous songliao basin of northeastern china an ideal place to study cretaceous climate change on the continent this paper reviews the literature on the paleogeography and paleoclimate of the northern east asia and the songliao basin during the cretaceous based on the climatolog ically sensitive deposits oxygen isotope studies and paleontology the climate during the cretaceous in the songliao basin was temperate and humid with relatively abundant rainfall during the period significant changes four cooling three warming and three semiarid events are generally consistent with the oxygen isotope data from east asia and the four cooling events in berriasian valanginian aptian albian early santonian and campanian maastrichtian may be related to potential glaciations in cretaceous

a comparison of foreland and rift margin sedimentary basins foreland and rift margin basins are compared on the basis of 1 their tectonic setting 2 reasons for subsidence and 3 their large scale geophysical and geological characteristics the thermal and mechanical properties of the underlying lithosphere are shown to be fundamental to the form of tectonic subsidence the lithosphere beneath foreland basins is flexurally downwarped by the loading of the adjacent fold thrust belt whereas tectonic subsidence at rifted margins is caused by mass replacement at depth during lithospheric extension on rifting and subsequent thermal contraction as the lithosphere cools the effects of rheology thermal maturity and lateral changes in properties of the lithosphere are outlined for foreland basins as is the topographic effect of possible phase changes beneath the fold thrust belt the thermal and rheological consequences of lithospheric extension at rift margins makes flexural subsidence relatively less important than in foreland basins flexure may however be partly responsible for uplift landward of the hinge line that is associated with rifting other mechanisms that could cause such uplift include depth dependent extension and thermal expansion due to the lateral diffusion of heat the models describing the evolution of these basins are shown to predict characteristics that are in accord with observations the superposition of foreland and rift margin basins as a result of ocean closure can lead to an overall basin stratigraphy that is complex such phases of basin subsidence must be separated according to the tectonic environment in which they formed in any analysis of the cause and consequences of basin evolution

the triassic and jurassic paleogeography and evolution of the qinghai xizang tibet plateau the kunlun qilian and qinling mountains already existed in embryonic form as coastal ranges in triassic times marine conditions predominated to the south the southern coastline is demarcated by the northern margin of the tertiary siwalik sediments the paleo landmass of longmenshan sichuan yunnan separated this sea from that of southwest china by jurassic times the coastline of the eurasian continent within what is now china had already moved southwards to a line along the kunlun and hengduan mountains mainly on the basis of differences between continental and oceanic crust several different seas can be distinguished the himalayan lhasa qiangtang hengduan and triangle seas together with the qaidam peninsula and xining bay triassic and jurassic transgressions and regressions of these seas are discussed in detail during carboniferous and permian times the lhasa and himalayan seas were joined together with the main gondwana plate to the south in triassic times when the india pakistan subconti

the sichuan basin southwest china a late proterozoic sinian petroleum province abstract the sichuan basin in southwest china is a large intracratonic sedimentary basin which first subsided in the late proterozoic sinian the basin has had a long complex subsidence history that has continued through to the present day tectonic subsidence curves indicate that in its early history the basin developed as a complicated extensional basin whose subsidence and tectonic history was polyphase much of the subsidence was driven by pulses of extension followed by thermal relaxation of the lithosphere the sichuan basin is an important petroleum base for the people s republic of china because of the discovery and development of over 60 gas fields and 10 oil fields one of the fields is the large weiyuan gas field which is considered to be both sourced and reservoired in late proterozoic sedimentary rocks these rocks are the late sinian carbonates of the dengying formation which form part of a thick platform yangtze platform succession that was deposited from the sinian to the silurian the weiyuan gas field occurs in a large anticlinal structure 53 26 km 850 km2 of which 200 km2 is prospective for gas up until 1988 91 wells had been drilled in the field and 40 were in production production is approximately 800 000 m3 day 28 3 million cubic feet day with total production to 1987 being 13 6 billion m3 480 billion cubic feet total reserves in the weiyuan gas field are estimated at 30 40 billon m3 1060 1410 billion cubic feet the sinian and earliest cambrian succession in the sichuan basin is highly prospective for the discovery of additional reserves of natural gas

cretaceous cenozoic tectonic history of the jiaojia fault and gold mineralization in the jiaodong peninsula china constraints from zircon u pb illite k ar and apatite fission track thermochronometry the jiaojia fault jjf in the jiaodong area of eastern china is an important nne trending structure that is subsidiary to the regional tancheng lujiang tan lu fault zone and hosts 1200 t of gold reserves contained in disseminated and stockwork ore dominantly in the footwall of the fault we present new zircon u pb apatite fission track and illite k ar data along the jjf and have delineated its tectonic history focusing on its formation and reactivation zircon u pb dating shows that the shangzhuang granite is a composite body with ages between 132 1 and 127 1 ma illite k ar ages for the fault s gouge range from 83 2 to 68 2 ma and the measured apatite fission track ages for ores are between 55 and 21 ma previous zircon u pb geochronology and structural studies suggest that the jjf was originally activated in the jurassic during 160 150 ma as a sinistral fault the jjf was a normal fault in the early cretaceous due to nw se orientated tension and ne sw compression which lasted from 135 to 120 ma this was followed by sinistral strike slip faulting due to nw se compression and ne sw tension during 120 110 ma and it changed to normal displacement at ca 110 ma our apatite fission track data analysis and thermal modeling of representative samples suggest that there was a subsequent dextral reactivation of the fault at ca 55 ma previous age data of ca 130 110 ma for gold mineralization along the jjf coincides with the early cretaceous magmatism and is coeval with the transition from normal faulting to sinistral strike slip faulting of the jjf in early cretaceous which is interpreted to be due to changing direction of the subducting pacific plate

tectonic features of oil and gas basins in eastern part of china during the mesozoic cenozoic eastern china underwent two stages of structural development sedimentary basins in eastern china have certain characteristics basement faults are well developed in these basins there was rapid sedimentation during the mesozoic cenozoic the basins are located on either side of the songliao depression the amount of subsidence in these basins is limited with a maximum depth of sedimentation of 4 000 to 6 000 m 13 000 to 20 000 ft during the mesozoic the most intense tectonic movements occurred in the songliao basin where there was much faulting accompanied by volcanic activity the bohai bay basin was the center of major tertiary tectonic activity there are more than 50 major basement faults in this basin basin formation was controlled primarily by movement of the pacific plate and related volcanic activity these basins are epicontinental basins along the margin of continental crust hydrocarbons were generated during the time of basin formation and much of the oil and gas discovered has been in rocks where it was generated or where migration was over short distances

meso cenozoic volcanic rocks in east china and adjacent areas with relation to plate tectonics abstract meso cenozoic calc alkaline volcanic rocks and granites in the east china region are composed of four ne belts from west to east the trassic belt in the middle and east mongolia the jurassic creta ceous belt in east china the paleogene belt in the east china sea and the neogene quaternary belt in southwestern japan okinawa and northeastern japan izu bonin mariana volcanic arcs they are nearly parallel to the benioff zones of the ancient pacific plate on one hand and become older as the distance from the pacific ocean increases on the other hand this sequence is in reverse order to that in south and north america there are two age peaks among them one is in the early cretaceous and the other in the miocene in good agreement with the time when the sea floor spreading of the ancient pacific plate became fast during 115 85 ma and after 25 ma hilde et al 1977 the second belt in east china consists of three paralleled ne sub belts and two e w sub belts on which the volcanoes erupted throughout the jurassic cretaceous period but the strong eruption centres were moving eastward with time the continental rift type basalts occurred in the middle of east china in paleogene time the neogene quaternary basalts in east china belong to crack type zheng and zao 1984 these ages and types of rocks suggest that subduction of the ancient pacific plate began at triassic time and became stronger later the meso cenozoic volcanic belts from north to south can be divided into three different regions by the tianshan xinganling and the qinling tectonic lines in the middle of east asia and two regions in the middle of the western pacific this difference has been getting clear since the triassic time on the whole the meso cenozoic volcanism in the middle of the western pacific records reaction between the asian plate and the ancient pacific plate or the indian plate

biological and sedimentary facies of australian salt lakes abstract four main types of salt lakes are recognized in australian 1 large playa lakes 2 small closed lakes or pans 3 crater lakes and 4 coastal lakes not connected to the sea basically all have an nacl chemistry biological and sedimentary facies characteristic of these salt lakes can be arranged into three basic groups which relate to particular phases in lake regimes these phases are 1 wet phases of ephemeral shallow lakes 2 dry lakes and 3 deep water lakes all elements of the salt lake biota with fossilizable remains are discussed with a detailed account of the palaeo ecological information they offer elements of the nonaquatic biota associated with salt lake sediments are also analysed sedimentary features of australian salt lakes pertinent to palaeoecology are discussed in the context of their association with the biota using numerous illustrations the distribution of the biota on lake floors for example its concentration in particular areas of the lake or its destruction during particular episodes such as lake filling and drying is mentioned in the context of recognizing different facies three major lake regime phases are presented with emphasis on the biological and sedimentary facies which characterize them the paper concludes with a brief discussion of the relevance of recognizing particular salt lake facies and changes in lake histories for the study of palaeoclimates and for mineral and oil exploration

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

post rift geodynamics of the songliao basin ne china origin and significance of t11 coniacian unconformity abstract the t11 unconformity lies between the qingshankou and yaojia formations in the post rifting sequence of the cretaceous songliao basin ne china it is intimately associated with petroleum reservoirs and considered to be a disconformity forming in the tectonic quiet stage we present the interpretations from new seismic surveys and cored sections of the cretaceous continental scientific drilling borehole ccsd sk 1 in order to resolve the nature and origin of t11 unconformity the t11 is often a low angle unconformity with underlying qingshankou formation having been deformed and eroded prior to deposition of the yaojia formation in the post rift evolution of the basin it marks an abrupt change from a deep lake to shallow lake or subaerial environment documented by reddening of the lacustrine mudstone extinction of the ostracod assemblages and a great increase of coarse detrital inputs the sharp change of depositional environment the truncation of gentle folds and the cluster of volcanic and paleoearthquake activities all happened simultaneously immediately before the development of t11 unconformity indicating a significant regional compressional uplift event in the basin the timing of the t11 unconformity formation is within the interval 88 86 2 ma correlations with coeval unconformities in other cretaceous sedimentary basins in eastern asia indicate that this compressional uplift coincided with an episode of global plate reorganization between the eurasian and paleo pacific plates that culminated at 88 87 ma during this short interval the northeast asian margin in eastern china south korea japan and russian far east experienced widespread violent volcanic and granite emplacement activity triggered by compression resulting from rapid and orthogonal slab subduction the post rift basin tectonic inversion occurred during t11 coniacian time thereafter the basin again evolved in an extension regime two subsidence phases in post rift history took place as the direct consequence of coniacian compression peak which defined the distribution of oil sources and reservoirs

geochemical and zircon u pb and hf isotopic study of the baijuhuajian metaluminous a type granite extension at 125 100 ma and its tectonic significance for south china abstract the early cretaceous baijuhuajian pluton is an a type granitic intrusion emplaced along the jiangshan shaoxing jssx fault zone in western zhejiang province se south china it intruded into a late jurassic volcanic basin bounded by proterozoic sandstone and siltstone the granite has a coarse grained porphyritic texture and is composed of alkali feldspar phenocrysts in a matrix of k feldspar quartz plagioclase and biotite the pluton has a clear a type geochemical signature e g it is metaluminous a cnk 1 0 and has high sio2 75 to 78 wt total alkalis na2o k2o 4 8 to 8 5 wt rare earth elements total ree 228 to 438 ppm hfse and fe feot feot mgo 0 87 to 0 97 on the other hand it is characterized by low cao 0 51 to 1 01 wt tio2 0 06 to 0 13 wt p2o5 below detection and sr 7 0 to 9 5 ppm the hypersolvus texture and fine grained groundmass indicate emplacement at a shallow depth shrimp u pb zircon dating yielded a weighted mean 206pb 238u age of 126 3 ma and zircons from this pluton give ehf t values between 0 52 and 4 24 suggesting the importance of juvenile material in the magma source most of the plutonic rocks in southeast china are calc alkaline subduction related intrusions of jurassic and cretaceous age previous studies suggested that the sparse a type granites in south china were emplaced in two episodes 190 155 ma in the inland area and 100 ma along the coastal area in se south china our study of the baijuhuajian granite together with the coeval suzhou a type granite 123 ma in jiangsu province defines an important extensional event between 125 and 100 ma considering the available data for the mesozoic igneous rocks in south china we suggest that subduction of the pacific plate in the mesozoic produced voluminous calc alkaline granitoids and volcanic rocks with a younging trend from west to east the a type granites were generated during periods of local extension at 190 155 ma and 125 100 ma perhaps corresponding to localized rollback of the pacific plate

a preliminary description of the gan hang failed rift southeastern china abstract the gan hang failed rift as defined by present day topography extends at least 450 km in length and 50 km in width it is a northeast southwest trending series of features spanning from hangzhou bay in zhejiang province into jiangxi province through fuzhou city southwest of fuzhou the rift splits into two portions one continuing along the southwestern trend and the other diverging westward the total extent of the rift cannot be defined at this time the rift is superimposed upon a major suture zone of caledonian or early mesozoic age the suture represents the fusing of the south china huanan and yangtze cratons perhaps in late triassic but for sure by late middle jurassic time the rifting was initiated and followed this older suture in part this time corresponds roughly to the middle stage of the yanshanian orogeny and to the subduction of the postulated pacific kula ridge southeast of the continental margin the total thickness of the sediments and volcanics filling the rift valley reaches more than 10 000 m peak intensity of extension was between late middle jurassic and middle to late cretaceous sedimentation within the rift was not continuous and is marked with periodic unconformities sediments within the rift include red beds sandstones siltstones mudstones conglomerates breccias tuffs and ignimbrites vertebrate fossils and dinosaur eggs are also found contemporaneous volcanics within and flanking the rift include basalts rhyolites granites gabbros dacites and andesites silicic volcanics are mostly attributed to caldera systems early basalts are tholeiitic and later change to alkaline olivine basalt bimodal volcanism is recognized peak intensity of volcanism ranges between 135 and 75 ma in early cenozoic time the area was a topographic low paleocene eocene sediments and evaporites are the last rocks to be deposited in the rift today the rift is delineated by major high angle faults the pingxiang guangfeng deep fault belt red beds and volcanically derived u deposits scismic study of p wave velocities has produced an earth model which shows substantial crustal thinning under the gan hang rift the region has been included in the southeastern china mesozoic fault depression system and has not generally been recognized as a distinct failed rift

phanerozoic plate boundaries in mainland se asia the himalayas and tibet recently available geological data on tibet yunnan and burma facilitate recognition of phanerozoic subduction systems and two continental fragments of gondwanaland which extend through mainland se asia a cambrian subduction system and 5 mesozoic early caenozoic collision belts are identified in the region indochina eastern thailand and central tibet accreted to china in the early triassic western se asia and s tibet separated from gondwanaland in the permian or early triassic and collided with asia in the late triassic and the western burma island arc system collided with asia in the jurassic upper triassic flysch and schist in the eastern indoburman ranges were accreted to western burma in the jurassic early cretaceous during eastward subduction and formation of a back arc thrust belt following collision of greater india with arc complexes to the n in the cretaceous and with tibet in the early eocene western burma moved northwards about 450 km along the sagaing namyin ridge thrust transform fault formation of the 3 major belts of tin granites and the porphyry copper deposits in the region took place in specific tectonic settings within the subduction systems and collision belts

thickening of young pacific lithosphere from high resolution rayleigh wave tomography a test of the conductive cooling model direct seismic measurements of the thickening of oceanic lithosphere away from the spreading axis are rare due to the remoteness of mid ocean ridges on the east pacific rise at 17 s there were two long term broadband ocean bottom seismometer deployments the melt and glimpse experiments these arrays spanned young pacific plate seafloor ranging in age from 0 to 8 ma combining these two data sets we describe the increase in rayleigh wave phase velocities for 16 100 s period as function of distance from the ridge with two parameterizations an arbitrary function of seafloor age and a simple polynomial function of age on the pacific and nazca plates although resolution analysis shows that 10 to 15 independent pieces of information about the age variation of phase velocity on the pacific plate can be resolved at periods of 50 s the three parameter polynomial model fits the data almost as well indicating a simple pattern of the evolution of structure with age to compare our observations to the predictions for the conductive cooling of the lithosphere we convert a thermal half space cooling model to shear velocity using anharmonic and anelastic contributions the patterns in the velocities are not consistent with simple conductive cooling the conductive cooling model under predicts the changes in phase velocity with age observed in the 20 to 78 s period range we observe significant changes in shear velocity in the asthenosphere at depths greater than conductive cooling should extend the asthenospheric low velocity zone is asymmetric dipping to the west with the lowest velocities beneath the pacific plate west of the spreading center the conductive cooling model also over predicts the shear velocities in the lithosphere by 0 2 km s these anomalies indicate that more complicated mantle flow and significant mantle heterogeneities such as melt are required

cretaceous cenozoic history of the southern tan lu fault zone apatite fission track and structural constraints from the dabie shan eastern china apatite fission track aft and structural data outline the late cretaceouscenozoic history of the southern tan lu fault zone tlfz one of asia s major faults the triassic jurassic dabie orogen earth s largest track of ultrahigh pressure rock exposure and its foreland the yangtze foreland fold thrust belt the fission track analyses utilized the independent z and n methods for age determination which yielded within error identical ages ages from triassic jurassic syn orogenic foreland sediments are younger than their depositional age and thus were reset a group of ages records rapid cooling following shallow emplacement of granitoids of the widespread latest jurassicearly cretaceous yanshanian magmatism most ages are 90 to 55 ma and document cooling following reheating at 110 90 ma the time when the basement units of the dabie shan were last at 200 jc this cooling coincides with rifting marked by the late cretaceouseocene red bed deposition in eastern china during this period the dabie basements units exhumed in the footwall of the tan lu fault with the qianshan basin in the hanging wall the associated stress field is transtensional nw trending principal extension direction the youngest fission track ages and temperature time path modeling point to enhanced cooling in the footwall of the tan lu and associated faults at 45f10 ma the related stress field is transtensional with the principal extension direction changing trend from nw to w it may be the far field expression of the india asia collision superposed on the back arc extension setting in eastern china a regional unconformity at f25 ma marks an upper bound for the inversion of the late cretaceouseocene rift structures during the neogene further subsidence in the eastern china basins was accommodated by sub horizontal ne sw extension and followed by the presently active nw se extension the tan lu fault along the eastern edge of the dabie shan had normal

seismic anisotropy in the upper mantle 2 predictions for current plate boundary flow models 1 the anisotropic seismic structure due to flow induced mineral alignment is investigated for a series of models designed to simulate deformation in the upper mantle within a few hundred kilometers of a plate boundary the orientation distributions of olivine enstatite aggregates evolve along streamlines of each flow model based on each grains plastic response to the local stress strain field the effective elastic tensor for these textured aggregates provides predictions of p wave anisotropy and shear wave splitting throughout the model space p and s travel time delay patterns and fast shear wave polarization angles are found to vary significantly with incidence angle for a given model comparison of predicted fast p direction for our method versus a finite strain based estimate shows that agreement is acceptable for much of the model space but notable differences occur in regions up to several tens of kilometers in size two dimensional models of spreading center flow are presented for slow and fast rates and for several cases in which the ridge migrates over the deeper mantle the effect of flow in the third dimension is addressed in a few calculations for one comparison of flow in the mantle wedge at a subduction zone the introduction of trench parallel flow causes significant changes in the predicted patterns of p wave anisotropy magnitude more than orientation and sks splitting

interactions of tethyan blocks and evolution of asian fold belts abstract two segments of the tethys ocean the northern palaeo tethys and the southern neo tethys were distinct in that the opening of the latter in late palaeozoic early mesozoic times coincided with or caused the closing of the former continental blocks formed by rifting of the major plates of china and india interacted with each other and with major cratonic blocks and produced the asian and the southeast asian fold belts central iran tibet and shan west malay were parts of the greater gondwanic indo arabian plate and these rifted away to create the neo tethys these together with other blocks of the palaeo tethys reduce the width of the tethys ocean as originally conceived the episodic asiatic orogenies relate to progressive southward and southwestward migration of the subduction and the collision zones the resultant fold belts except for the unique himalayan belt which is a reworked microcontinent can generally be compared in geological and tectonic development from southeast asia to west central asia

geodynamics of the baikal rift zone and plate tectonics of asia the baikal rift zone stretches from the southern termination of lake baikal as far as 118 e and includes the baikal basin and the barguzin upper angara and muysk grabens that form its easterly continuation coincident with the rift zone is a narrow seismic belt which extends further east along the stanovoy range to the okhotsk sea this belt can be considered as the boundary between the eurasian and amurian lithospheric plates earthquake focal mechanism solutions that show a consistent orientation of extensional axes across the strike of the rift zone indicate the behaviour of the eurasian and amurian plates as rigid bodies from 83 focal mechanism solutions the pole of rotation of the eurasian and amurian plates was computed to lie at the point 56 95n 117 45e the angular rate estimated from the amount of baikal opening is about 1 10 7 deg year the position of the pole at the eastern termination of the rift zone accounts for the dying out of the rift zone and for the appearance east of the pole of compressive structures in the stanovoy range to the southwest the baikal rift zone is replaced by the mosaic of microplates in central asia that occupy the space between the eurasian and indian lithospheric plates prominent are the mongolian dzungarian alashan tarim tibetan and pamir microplates earthquakes in central asia are dispersed although higher concentrations of earthquakes associated with microplate boundaries are prominent the tectonics of central asia are considered to be due to the interaction of rigid microplates assuming that plastic deformations occur within the relatively wide zones along the microplate boundaries by considering the strike slip faults to define the trajectories of microplate motions the parameters of relative movements of the microplates have been computed the microplate mosaic of central asia is moving northeasterly as a result of the collision and continued convergence of india and eurasia the mosaic acts as a wedge splitting off the amurian plate from eurasia causing it to rotate counterclockwise so opening the baikal rift

sedimentary record and tectonic implications of mesozoic rifting in southeast mongolia the east gobi basin of mongolia is a poorly described late jurassic early cretaceous extensional province that holds great importance for reconstructions of mesozoic tectonics and paleogeography of eastern asia extension is especially well recorded in the structure and stratigraphy of the unegt and zuunbayan subbasins southwest of saynshand mongolia where outcrop and subsurface relationships permit recognition of prerift synrift and postrift mesozoic stratigraphic megasequences within the synrift megasequence three sequences developed in response to climatic and rift related structural controls on sedimentation where best exposed along the northern margin of the unegt subbasin each of the synrift sequences is bounded by unconformities and generally fines upward from basal alluvial and fluvial conglomerate to fluvial and lacustrine sandstone and mudstone resedimented ashes and basalt flows punctuate the synrift megasequence rifting began in the unegt subbasin prior to 155 ma with coarse alluvial filling of local fault depressions subsidence generally outstripped sediment supply and fresh to saline lacustrine environments expanding southward with time dominated the unegt zuunbayan landscape for much of latest jurassic early cretaceous time episodic faulting and volcanism characterized the basin system for the balance of the early cretaceous a brief period of compressional and or transpressional basin inversion occurred at the end of the early cretaceous prior to deposition of a widespread upper cretaceous overlap sequence the driver s of late jurassic early cretaceous extension remain uncertain because southeast mongolia occupied an intraplate position by the beginning of the cretaceous extension in the east gobi basin was coeval with collapse and extension of early mesozoic contractional orogenic belts along the northern and southern borders of mongolia and probably was a linked phenomenon strike slip faulting associated with collisions on the southern asian and mongol okhotsk margins likely also played a role in late mesozoic deformation of the east gobi region perhaps partitioning the gobi from apparently coeval large magnitude contractional deformation in the yinshan yanshan orogenic belt south of the study area in inner mongolia

the pearl river mouth basin a rift basin and its geodynamic relationship with the southeastern eurasian margin abstract based on multichannel seismic reflection profiles exploration well data and gravity studies the tectonic development of the pearl river mouth basin is discussed in terms of the geodynamic evolution of the southeastern eurasian margin the area around the pearl river mouth basin has been dominated by two episodes of rifting of the attenuated continental crust along the south china margin from the late cretaceous to the early oligocene the rifting brought about ruptures of various magnitudes in various segments of the basin regional normal faults have been produced and resulted in the formation of three major subbasins zhu 1 zhu 2 and zhu 3 which are separated by local uplifts and are characterized by horst and graben structures regional subsidence prevailed throughout the late oligocene recent period and resulted in a tilted continental shelf upon which rests a unified rift basin the pearl river mouth basin a three stage model involving doming rifting and drifting is proposed for the tectonic evolution of the pearl river mouth basin the uplifting and rifting of the continental crust along the south china margin are related to the late episodes of the yanshan orogeny during the late cretaceous early oligocene period when the intensity of rifting decreased the thermal subsidence of the continental margin of south china prevailed during the late oligocene recent period of the himalaya orogeny

fragmentation of asia in the permian asia is a composite continent formed by the accretion of crustal blocks1 3 a likely sequence of events is that siberia collided with a kazakhstan block which together then collided with europe along the urals in permo triassic times2 this was followed by the sucessive accretion of various blocks of south and east asia to siberia culminating in the collision of india with asia during the cenozoic palaeomagnetic data have already demonstrated that the kolyma and sikhote alin blocks of eastern asia collided with the main continent along the late mesozoic fold belts of verkhoyansk and sikhote alin4 furthermore results from the malay peninsula5 and japan6 suggest that south east asia and japan were situated near the equator in permian times and were therefore separated from the asian continent we report here some palaeomagnetic results from the permian of the sino korean and yangtze blocks of china that show they were also situated near the equator were not in their present relationship to one another and were widely separated from siberia

jizhong depression china its geologic framework evolutionary history and distribution of hydrocarbons jizhong depression is located in the northwestern part of the north china basin extensive seismic work and exploratory drilling have led to the discovery of several oil fields including renqiu field after detailed analysis of this area the writer came to the following conclusions 1 eleven major pre tertiary blocks present in this depression are the products of the himalayan orogeny but were controlled by the structural pattern of the yenshan movement 2 the center of block faulting gradually shifted activity had a pulsating pattern sometimes stronger and sometimes weaker these blocks have been subjected to multiple processes of disruption and combination not only by tensile but also by torsional stresses 3 the development of block activities led to uniqu sedimentary buildups in each period 4 at least 10 types of traps have been identified each of them has a definite spatial distribution in this area there are mainly three series of oil and gas pools buried hill tertiary and paleozoic sinian because most of the exploration efforts in this area have been expended on the buried hill there still is excellent potential for future petroleum exploration in the jizhong depression

structure stratigraphy and basin subsidence of tertiary basins along the chinese southeastern continental margin abstract in southeastern china offshore tertiary basins extend along the broad continental shelf from taiwan to hainan island these basins share similar characteristics of structure stratigraphy and tectonics based on their age and tectonic framework these tertiary basins can be divided into paleogene basins and neogene basins however observations of extensional structures indicate that the paleogene basins are rift basins with predominant structural features of ne sw trending half grabens and fault blocks on a regional scale these half grabens and adjacent uplifts represent a horst and graben structural style neogene basins are downwarp basins lying on the tilting continental shelf upper tertiary sequences are relatively undeformed but locally exhibit minor pliocene pleistocene folding and faulting seismic stratigraphy and well data indicate that the early tertiary strata are commonly tilted and were structurally disturbed as nonmarine to marginal marine facies that were deposited in the wedge shaped half grabens late tertiary strata are generally undisturbed marine facies which accumulated in the enlarged downwarp basins overlying the infilled half grabens the tectonic history of these basins shows two stages of basin subsidence first early basement rifting and basin subsidence accompanying displacement along the border faults formed the half grabens which received sediments in the late cretaceous to middle eocene second late thermal subsidence owing to cooling of the continental crust predominated and resulted in a tilting and subsiding continental shelf upon which relatively flat marine facies were deposited in the late tertiary

climatic and environmental indications of carbon and oxygen isotopes from the lower cretaceous calcrete and lacustrine carbonates in southeast and northwest china abstract carbon and oxygen isotopic ratios were determined from 100 lower cretaceous samples from four carbonate bearing facies in southeast se and northwest nw china for palaeoclimatic and palaeoenvironmental analyses the samples were interpreted as sediments within sublithofacies of distal alluvial ponds sf1 open shallow lakes sf2 littoral lakes sf3 and marshes sf4 results of analyses show in se china 13c values range between 5 0 and 3 0 with a negative trend through time and 18o values are all negative 19 3 7 4 in nw china 13c values range from 4 0 to 4 0 with periodic change and 18o values range between 18 0 and 1 5 both relatively heavy values and pronounced covariances of most 13c and 18o indicate semiarid climate and domination of closed brackish lakes marshes and ponds in nw and se china during the early cretaceous of them positive 13c 0 0 to 4 0 and relatively heavy 18o 5 0 to 1 5 values suggest interruptions of arid evaporation in intermittences of the early hauterivian in sw fujian of the middle aptian in west jiuquan basin of the late aptian in sw ordos basin and of the late aptian early albian in liupanshan basin in a short interval of the early aptian the hot and humid climate occurred in local sw zhejiang by high kaolinite content and in west jiuquan basin by warm flora could be an exception particularly extremely negative 18o values mainly 19 0 9 0 indicate relatively low temperature in se fujian in the berriasian barremian in liupanshan basin in the late aptian in sw ordos basin in the late albian and in west jiuquan basin in the mid late aptian which is supposed to attribute to the presence of 2500 m 4500 m in elevation more positive values and more covariance ratios of 13c and 18o in nw china than in se china and in mainland china than in america indicate a arider climate in former than in later probably attributing to the palaeogeography in distance to sea a tentative correlation of the early cretaceous 13c value excursion of calcretes shows a good compatibility between marine oaes and terrestrial carbonate sediments and between nw china and america continents implying a global response to carbon cycle in both marine and terrestrial environments the feature suggests the potential of global correlation and application of terrestrial calcrete 13c excursions in pre cenozoic