mesozoic structural evolution of the hangjinqi area in the northern ordos basin north china abstract this study analyzes the structural evolution of the hangjinqi area in the northern ordos basin based on seismic sections and exploration well data this area shows excellent examples of the relationship between tectonics and sedimentation three tectonic sequences separated by four erosional surfaces have been recognized overlying a paleoslope surface t9 in this area 1 the late carboniferous permian and triassic tectonic sequence ts 1 sedimentation of the lowest part of this succession is strongly controlled by the hangjinqi fault zone hfz whereas the rest of the sequence indicates much less fault control 2 the middle jurassic tectonic sequence ts 2 3 the late early cretaceous tectonic sequence ts 3 and the ts 2 and ts 3 sequences are more extensive than the ts 1 sequence throughout the hangjinqi area the structural framework displayed by the ts 2 sequence is very different from that displayed by the ts 3 sequence more specifically the general structure beneath the unconformity t3 between the late jurassic strata and the early cretaceous strata consists of an e w trending transtensional fault system this resulted from a multi stage dextral phase which was caused by oblique subduction of the paleo pacific plate under the eurasian plate and dextral movement of the hfz and a subsequent inversion event which caused significant reverse movement along previous transtensional structures the study area which underlies the unconformity t2 between the late jurassic strata and the early cretaceous strata has been deformed since the late cretaceous when tectonic inversion occurred possibly due to changes in the strike slip motion from dextral to sinistral of the hfz late cretaceous erosion was responsible for an important and unequal denudation the timing of the transition from extension to uplift cannot be determined due to continuous erosion but this uplift finally marked the end of the structural evolution of the hanjinqi area and even the ordos 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

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

occurrence of pyrites in sandstone type uranium deposits relationships with uranium mineralization in the north ordos basin china abstract large quantities of pyrite have been discovered near the ore bearing segments of the sandstone type uranium deposits in the north ordos basin in this study the electron probe microanalysis scanning electron microscopy and isotope geochemical analysis were used to systematically investigate the morphology composition and s isotopes of the pyrites in these deposits and their genetic order relative to the other main altered minerals based on the regional tectonic evolutionary sequence of the basin the relationships between the pyrites and uranium mineralization are discussed macroscopically the pyrites were found to occur in lumpy banded disseminated star like or sheet like form microscopically they exist either as detrital grains or inside detrital grains as idiomorphic grains in colloidal or framboidal form inside mica minerals in banded or petaloid form and in other forms related to biological cells or microorganisms the 34s values in the pyrites are highly variable 7 3 to 37 2 but principally in the proximity of 30 and display obvious biogenic origin taking into consideration the extremely low u contents in the pyrites and achavalites iron selenide the genetic order of the main altered minerals is determined as follows detrital pyrites clay mineral overgrowths micritic calcites during the diagenetic stage and achavalites pyrites coffinite pitchblende vanadium oxides sparry calcites during the metallogenic stage the broad presence of pyrites in the jurassic yan an formation during the basin s evolution provided detrital pyrites and organic detritus for the overlying formations the zhiluo formation host of the uranium mineralization is also home to some primary spherical colloidal or framboidal pyrites the cretaceous was the main epigenetic uranium metallogenetic period as well as the main pyrite development period of the area the pyrites which are typically colloidal have cemented the earlier framboidal pyrites and other minerals and are closely associated with the redox reaction related to uranium mineralization in the paleogene uranium mineralization mainly occurred by the redox migration of early shallow deposits to and fresh pyrites forming in deeper levels

circulation on the central bering sea shelf july 2008 to july 2010 1 we examine the july 2008 to july 2010 circulation over the central bering sea shelf using measurements at eight instrumented moorings hindcast winds and numerical model results at sub tidal time scales the vertically integrated equations of motion show that the cross shelf balance is primarily geostrophic the along shelf balance is also mainly geostrophic but local accelerations wind stress and bottom friction account for 10 40 of the momentum balance depending on season and water depth the shelf exhibits highly variable flow with small water column average vector mean speeds 5 cm s 1 mean peak speeds in summer 3 6 cm s 1 10 30 cm s 1 are smaller than in winter and fall 6 12 cm s 1 30 70 cm s 1 low frequency flows 1 4 cpd are horizontally coherent over distances exceeding 200 km vertical coherence varies seasonally degrading with the onset of summer stratification because effects of heating and freezing are enhanced in shallow waters warm summers increase the cross shelf density gradient and thus enhance northward transport cold winters with increased ice production and brine rejection increase the now reversed cross shelf density gradient and enhance southward transport although the baroclinic velocity is large enough to influence seasonal transports wind forced ekman dynamics are primarily responsible for flow variations the system changes from strong northward flow with coastal convergence to strong southward flow with coastal divergence for northerly and easterly winds respectively under northerly and northwesterly winds nutrient rich waters flow toward the central shelf from the north and northwest replacing dilute coastal waters that are carried south and west

motion of the pacific plate relative to eurasia and its potential relation to cenozoic extension along the eastern margin of eurasia extension along the eastern margin of eurasia has been regarded commonly as a far field effect of the india eurasia collision however some aspects of the timing and location of this extension make a link between the collision and extension difficult we suggest that some extensional features commonly interpreted as effects of the collision may be related more simply to changes in plate convergence rates along the eastern plate boundary of eurasia an analysis of the motion of the pacific plate relative to eurasia suggests that the rate of pacific eurasia convergence varied significantly during the tertiary period from a late cretaceous convergence rate of 120 140 mm yr the rate declined substantially during early tertiary time and reached a minimum in eocene time of 30 40 mm yr in oligocene to earliest miocene time the average convergence rate increased moderately to 70 95 mm yr then decreased again to 65 70 mm yr during early to middle miocene time from late miocene to the present the rate of convergence increased to an average of 100 110 mm yr the paleocene through middle miocene episode of relatively slow convergence correlates with a period of widespread extension along the eastern margin of eurasia decreased convergence may have been related to a net reduction in horizontal compressional stress transmitted between the pacific and eurasian plates which resulted in widespread extension adjacent to the margin of eurasia

late cretaceous cenozoic exhumation of the helanshan mt range western ordos fold thrust belt china insights from structural and apatite fission track analyses abstract the western ordos fold thrust belt is an intracontinental chain predominately formed in the jurassic and subsequently reworked in the late cretaceous and cenozoic the structural deformation of the western ordos fold thrust belt was driven by the force transmitted from the plate boundary of asian collage this study presents new structural analysis apatite fission track and thermal modeling data in the helanshan mt range of the western ordos fold thrust belt the apatite fission track analysis and thermal modeling suggest that the helanshan mt range underwent two stages of cooling and exhumation since the late cretaceous the first fast cooling stage in the late cretaceous 90 70 ma led to ca 1 1 2 km exhumation and the second fast cooling was after ca 30 ma with an exhumation of ca 1 8 2 2 km structural studies indicate that the late cretaceous exhumation was related to nw se compression and the exhumation of after ca 30 ma was associated with wnw ese transtension the wnw ese transtension produced high angle normal faults by reworking the mesozoic pre existing factures comprehensive analyses of the synchronous structures around the boundaries of the asian collage suggest that the late cretaceous exhumation of the helanshan mt range might be the far field results of the convergence between the pacific and eurasian plates the varying rates of the pacific plate subduction may transmit nw sw horizontal stress across the north china plate in contrast the post oligocene

low frequency current regimes over the bering sea shelf abstract using direct current measurements made during the period 1975 81 we describe the general circulation over the southeastern bering sea and differentiate it by regimes related to depth and forcing mechanisms three regimes are present delineated by water depth z the coastal z 50 m the middle shelf 50 z 100 m and the outer shelf z 100 m these are nearly coincident with previously described hydrographic domains statistically significant mean flow 1 to 10 cm s 1 exists over the outer shelf generally directed toward the northwest but with a cross isobath component flow of similar magnitude 1 6 cm s 1 occurs in the coastal regime paralleling the 50 m isobath in a counterclockwise sense around the shelf mean flow in the middle shelf is insignificant kinetic energy at frequencies 0 5 cycle per day cpd is greater over the outer shelf than in the other two regimes suggesting that oceanic forcing is important there but does not affect the remainder of the shelf kinetic

modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates abstract a parallel ocean and ice model poim in generalized orthogonal curvilinear coordinates has been developed for global climate studies the poim couples the parallel ocean program pop with a 12 category thickness and enthalpy distribution ted sea ice model although the poim aims at modeling the global ocean and sea ice system the focus of this study is on the presentation implementation and evaluation of the ted sea ice model in a generalized coordinate system the ted sea ice model is a dynamic thermodynamic model that also explicitly simulates sea ice ridging using a viscous plastic rheology the ted model is formulated such that all the metric terms in generalized curvilinear coordinates are retained following the pop s structure for parallel computation the ted model is designed to be run on a variety of computer architectures parallel serial or vector when run on a computer cluster with 10 parallel processors the parallel performance of the poim is close to that of a correspon

exhumation of the ultrahigh pressure continental crust in east central china cretaceous and cenozoic unroofing and the tan lu fault the orogenic architecture of the world s largest ultrahigh pressure exposure the hong an dabie mountains of the triassic qinling dabie orogenic belt is dominated by cretaceous and cenozoic structures that contributed to its exhumation from 30 km depth cretaceous magmatic crustal recycling 50 for the entire dabie and heating 250 to 700 c were most prominent in dabie and exhumation magmatism and cooling were all controlled by cretaceous transtension exhumation was accomplished principally by an asymmetric cordilleran type extensional complex in the northern dabie northern orthogneiss unit between 140 and 120 ma at rates as fast as 2 mm yr and average horizontal stretching rates of up to 6 mm yr cretaceous reactivation occurred within a regional transtensional strain field as a result of far field collisions and pacific subduction the onset of crustal extension was preceded and possibly facilitated by a reheating of the hong an dabie crust 140 ma coeval with the onset of voluminous magmatism in eastern china 145 ma which resulted from a change in pacific subduction from highly oblique to orthogonal the tan lu continental scale fault was a normal fault zone in the mid cretaceous 110 90 ma and underwent 5 4 km dip slip and 4 km throw in the cenozoic during the india asia collision the qinling dabie belt acted as the structural discontinuity between the strike slip dominated escape tectonics south of the qilian qinling dabie belt and the rifting dominated tectonism north of it the most prominent cretaceous and cenozoic structures of the hong an dabie the xiaotian mozitang and the jinzhai fault zones respectively reactivated major lithospheric structures of the triassic orogen i e the huwan detachment zone and the suture

tectonic and stratigraphic controls of hydrocarbon systems in the ordos basin a multicycle cratonic basin in central china the ordos basin is the oldest and still an important hydrocarbon province in central china it is a typical cratonic basin developed on the archean granulites and lower proterozoic greenschists of the north china block the development of the ordos basin during the paleozoic mesozoic can be divided into three evolutionary stages cambrian early ordovician cratonic basin with divergent margins middle ordovician middle triassic cratonic basin with convergent margins and late triassic early cretaceous intraplate remnant cratonic basin two hydrocarbon systems are present in the basin the paleozoic gas and mesozoic oil systems in the paleozoic gas system the lower ordovician marine carbonates and pennsylvanian lower permian coal measures serve as source rocks the lower ordovician karst modified dolomites and pennsylvanian bauxitic mudstones form a significant reservoir seal association and the pennsylvanian lower permian deltaic sandstones and upper permian lacustrine mudstones form another effective reservoir seal association in the mesozoic oil system the upper triassic lacustrine mudstones are mature source rocks the upper triassic deltaic sandstones and overlying shallow lacustrine and swamp mudstones form a reservoir seal association and the lower jurassic fluvial sandstones and overlying shallow lacustrine and swamp mudstones form another reservoir seal association in both hydrocarbon systems the stratigraphic variations provide the principal traps the ordos basin is characterized by a stable tectonic setting that controlled the distribution of depositional systems and the development of erosional surfaces and ultimately governed the distribution of oil and gas fields and trap types

the goodman swell a lithospheric flexure caused by crustal loading along the midcontinent rift system rb sr biotite ages of archean and early to middle proterozoic crystalline rocks in northern wisconsin and adjacent upper peninsula of michigan describe a regionally systematic pattern related to differential uplift an age low occurs in northern wisconsin where values range from 1070 1172 ma for rocks with crystallization ages of 1760 to 1865 ma these values overlap with the main episode of mafic igneous activity 1090 to 1120 ma along the midcontinent rift system mrs we interpret these low biotite ages as registering closure due to cooling below the 300 c isotherm as a consequence of uplift and rapid erosion of an area that we are informally naming the goodman swell the position of the goodman swell is independent of the archean and early proterozoic regional geologic framework but closely linked with the curvilinear concave to the south mrs we interpret the swell to be a forebulge imposed on an elastic crust by loading of mafic igneous rocks along and within the axis of the mrs the southward concavity of load axes resulted in flexural interaction that localized the swell because of rapid uplift the swell may have been a source area for clastic sediments in the rift sequence

factors influencing physical structure and lower trophic levels of the eastern bering sea shelf in 2005 sea ice tides and winds abstract in spring and fall 2005 cross and along shelf transects were sampled to evaluate the influence of physical forcing including sea ice tides and winds on the lower trophic levels of the bering sea ecosystem the hydrography nutrients chlorophyll and zooplankton abundance and species composition were all affected by the presence or absence of sea ice on a north south transect along the 70 m isobath in may shelf waters between 59 n and 62 n were cold and relatively fresh and benthic invertebrate larvae and chaetognaths were a significant fraction of the zooplankton community while to the south the water was warmer saltier and the zooplankton community was dominated by copepods the position of the transition between ice affected and ice free portions of the shelf was consistent among temperature salinity nutrients and oxygen this transition in the hydrographic variables persisted through the summer but it shifted 150 km northward as the season progressed while a transition also occurred in zooplankton species composition it was farther north than the physical chemical transition and did not persist through the summer mooring data demonstrated that the change in the position of the transition in physical and chemical properties was due to northward or eastward advection of water onto and across the shelf from south to north along the 70 m isobath tidal energy decreased resulting in a less sharply stratified water column on the northern portion of the middle shelf as opposed to a well defined two layered system in the southern portion this more gradual stratification in the north permitted a greater response to mixing from winds which were homogeneous from north to south thus the physical and biological structure at any one location over the middle shelf is dynamic over the course of a year and results from a combination of in situ processes and climate mediated regional forcing which is dominated in most years by sea ice

winter currents and hydrographic conditions on the northern central bering sea shelf current observations obtained from the northern bering shelf region in winter 1984 1985 indicate that midwinter circulation patterns differed from those during the rest of the year annual mean circulation in this region is dominated by vigorous northward currents from 10 cm s in shpanberg strait to more than 50 cm s in bering strait these northward currents are accompanied by a weak northwestward coastal flow south of st lawrence island in february april 1985 however flow was weakly 0 5 cm s southward through shpanberg strait and southeastward south of st lawrence island while remaining northward through anadyr and bering straits comparison with current data obtained from previous years suggests that midwinter reversal of flow in shpanberg strait is a recurrent winter feature it generally occurs at about the same time that the winter ice cover undergoes its major advance and it is associated with strong northerly winds northward flow through anadyr strait persists conversely through the winter and is the northward extension of a western intensified northward flow over the bering shelf its source is bering sea water farther south rather than water from the northern central shelf the resultant trapping of shelf water on the northern central shelf coupled with intensive regional ice formation during the same period as the flow reversal led in 1985 to significant about 1 5 brine enrichment this salinity increase agrees qualitatively with historical data which suggest that the northern central bering shelf is the site both of sluggish winter circulation and of elevated salinities due to brine enrichment from ice formation

subinertial currents on the southern califoinia shelf abstract subinertial currents on the southern california shelf are investigated using observations from a current meter array deployed near san diego during the summer fall and winter of 1978 79 this region is characterized by weak winds order 1 2 m s 1 and thus other driving mechanisms for the subinertial currents may be important a simplified depth averaged longshore momentum equation consisting of a balance between current accelerations the adjusted sea level asl gradient and the wind and bottom stress is examined the asl gradient is estimated using sea level and atmospheric pressure observations separated by 350 km a linear parameterization of the bottom stress is used with a drag coefficient of 5 10 4 m s 1 during fall and winter the first order balance of terms in the longshore momentum equation over the inner shelf 15 m depth is between the wind and bottom stress over the outer shelf 60 m the primary balance is between the asl gradient and the bottom stress at midshelf 30 m bo

identification characterization and change of the near surface temperature maximum in the canada basin 1993 2008 1 sea ice in the canada basin of the arctic ocean has decreased significantly in recent years and this will likely change the properties of the surface waters a near surface temperature maximum nstm at typical depths of 25 35 m has been previously described however its formation mechanisms seasonal evolution and interannual variability have not been established based on summertime conductivity temperature and depth surveys and year round ice tethered profiler data from 2005 to 2008 we found that the nstm forms when sufficient solar radiation warms the upper ocean a seasonal halocline forms in summer once enough sea ice melt has accumulated to separate the surface mixed layer from the nstm the nstm becomes trapped below the summer halocline thereby storing heat from solar radiation this heat can be stored year round in the canada basin if the halocline is strong enough to persist through winter in addition energy from storm driven mixing can weaken the summer halocline and entrain the nstm thereby melting sea ice in winter throughout this cycle ekman pumping within the convergent beaufort gyre acts to deepen the nstm from 1993 through 2007 the nstm warmed and expanded northward and both the nstm and the summer halocline formed at successively shallower depths north of 75 n the temperature of the nstm increased from 2004 to 2007 by 0 13 c yr and the nstm and summer halocline shoaled by 2 1 m yr and 1 7 m yr respectively from 1997 to 2007 the formation and dynamics of the nstm are manifestations of both the ice albedo feedback effect and changes to the freshwater cycle in the canada basin

the north pacific a global scale estuary abstract the atmospheric net flow of water from the atlantic to the pacific ocean is supposed to maintain the salinity difference between the two oceans assuming the existence of a subsurface level of no horizontal pressure gradient in the ocean the mean sea level in the northern pacific must be higher than in the arctic ocean this mean sea level difference is supposed to drive the observed mean flow through the bering strait the estimated flow of freshwater through the bering strait is approximately equal to the estimated atmospheric net flow of water from the north atlantic to the north pacific this justifies the formulation of a simple estuary model for the north pacific in which the brackish water exits through the bering strait the salinity difference between the two oceans is shown to be controlled by the topography of the bering strait the estuary model gives residence times for water in the upper layer 1000 m thick of approximately 1000 years and in the lower layer of approximately 400

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

timing of collision of the north and south china blocks controversy and reconciliation the qinling orogen was formed by the joining of the north and south china blocks but the timing of their integration has been debated for more than a decade the controversies obviously stem from different approaches to reconstruction of the integration history two contrasting lines of evidence yield two different ages for collision of the north and south china blocks middle paleozoic and late triassic the shangdan suture within the qinling was regarded in previous studies as the trace along which the north and south china blocks collided our studies however demonstrate that there are two sutures within the qinling the well documented shangdan suture and the newly discovered mianlue suture we show in this paper that the late proterozoic to early mesozoic evolution of the qinling involved interactions between the north china block the north and south qinling orogens and the south china block the middle paleozoic collision along the shangdan suture as constrained by some evidence accreted only the south qinling orogen to the southern part i e the north qinling of the north china block contemporaneous rifting of the south china block and subsequent drifting separated the south qinling from the south china block during the middle to late paleozoic the separation of the south from the north china blocks is supported by other evidence in particular geomagnetic data evidently it was the late triassic collision of the south china block with the south qinling orogen along the mianlue suture that led to final integration of the north and south china blocks

the implication of the geophysical data and drilling records for the formation and paleoenvironment of the hobq desert china abstract the hobq desert hd locates at the northern margin of the ordos plateau china and the transition zone to the hetao basin it is one of the main proximal deserts of the loess plateau and its formation was controlled by the evolution of the yellow river and the ordos plateau it is still worthy of discussing the regional structure to enhance the understanding of the desert formation and paleoenvironment especially with the additional works in the eastern part geophysical methods including gravity magnetic em electromagnetic are often used to analyse the regional and near surface structure as for drilling records they could show the lithology sequence directly and be applied for the environmental study e g osl dating therefore in this paper we used the satellite gravity data gpr ground penetrating radar tem transient electromagnetic method and drilling records with borehole resistivity data to analyse the desert structure from different scales and the paleoenvironment trough the upward continuation and park oldenburg calculation for the gravity data the thickness of quaternary deposits is 0 85 1 55 km the inferred faults indicated the performance of the hetao basin and the ordos plateau s uplift in pleistocene which also contributed to hd s formation and existing topography a three part structure within 350 m was revealed in the profile at eastern hd by em data the upper layer within 80 90 m was the aeolian dry sand the middle one was mainly fluviolacustrine saturated sand with the occurrence of clay and grey calcareous root tubes and the lower one might be the aeolian sand this near surface structure was consistent to the western part and the forming period for the sand in the upper zone was thereby estimated no earlier than 80 ka moreover during this period millennial scale changes in paleo effective moisture occurred although it was dominated by the arid climate

a numerical study of the circulation of the bering sea basin and exchange with the north pacific ocean abstract a limited area primitive equation three layer hydrodynamic model with realistic coastlines and bathymetry and resolution is used to investigate the circulation of the bering sea basin and the adjacent north pacific ocean the westward flowing alaskan stream to the south of the aleutian island chain is specified as a boundary condition at inflow and outflow ports with a constant throughput of 15 sv sv 1 106 m3 s 1 atmospheric forcing is based an the hellerman and rosenstein monthly climatological wind field the model is spun up over 50 years and the statistics of the final decade are described the general features of the model circulation as discussed below are consistent with available hydrographic and buoy drift observations the model alaskan stream separates from the aleutian island chain near 175 beyond this point there is strong interannual variability associated with meandering and occasional eddy shedding along the northern arm of the western subarctic gyre there is a gen

implications of crustal property variations for models of tibetan plateau evolution shear coupled teleseismic p waves sampling the interior of the tibetan plateau provide evidence of systematic variations in crustal structure the crust thins by up to 20 km from south to north with a concomitant increase in poisson s ratio from normal values in the south to unusually high values in the north this suggests that the crust of the northern plateau is partially melted due to high temperatures these changes imply spatial and perhaps temporal variations in the way the elevation of the high plateau is created and maintained

observations of the aleutian north slope current bering sea 1996 2001 1 cyclonic circulation dominates flow in the bering sea basin the eastward flowing aleutian north slope current ansc flows along the north slope of the aleutian islands turning northwestward in the southeast corner of the basin to form the bering slope current bsc during the period 1997 to 2007 a pair of hydrographic lines was occupied 14 times in the southeastern portion of the basin one transect was across the ansc and the second was across the bsc in addition a series of five yearlong moorings was deployed in a water depth of 1000 m in the ansc and a single yearlong mooring was deployed to the northeast in a water depth of 2200 m at the primary mooring site strong variability in temperature and salinity occurred at fortnightly and annual periods while strong variability in the currents occurred at fortnightly and semiannual periods the mean geostrophic flow relative to 1500 m calculated from the 14 occupations of the hydrographic lines was 3 1 106 m3 s 1 in the ansc and 3 3 106 m3 s 1 in the bsc a significant barotropic component measured by the current meters adds 3 106 m3 s 1 to the transport

on exchange of water between the gulf of alaska and the bering sea through unimak pass we present the first long term current and bottom pressure observations from unimak pass alaska and adjacent locations on the gulf of alaska and bering sea shelves vector mean current recorded between march and august 1980 was 12 cm s toward 284 t or onto the bering sea shelf however magnitude decreased from 20 cm s to 6 cm s between the first and second halves of the record at shorter periods 3 10 days current fluctuations in the pass were strongly coherent k2 0 7 with the pressure difference measured along the axis of the pass and this was coherent with geostrophic wind estimates the results indicated that wind induced sea level perturbation was the dominant forcing mechanism for fluctuations relations among current bottom pressure pressure difference and geostrophic wind time series also showed that dynamic variaton on the gulf of alaska shelf was primarily responsible for current fluctuations in the pass hydrographic data indicated that a baroclinic current existed along the gulf of alaska coast and this flow became the long term mean flow through the pass we suggest that this feature was the extension of the kenai current the historic supposition that water is transported from the gulf of alaska into the bering sea was verified however the waters are of coastal origin rather than from the alaskan stream

segmentation and inversion of the hangjinqi fault zone the northern ordos basin north china abstract this paper deals with the segmentation and inversion of the hangjinqi fault zone hfz which is the dominant structure in the northern part of the ordos basin in north china hfz was reactivated during the late triassic and obliquely inverted during the middle jurassic shortening subsurface geological mapping and structural analysis were carried out to determine the segmentation and kinematic history of the deformation the hfz was a left stepping fault zone and was made up of three segments the porjianghaizi fault pf wulanjilinmiao fault wf and sanyanjing fault sf which are separated by two relay ramps two distinct phases can be identified in its structural evolution 1 during the late triassic compressional deformation the hfz was characterized by shortening and thrusting to the north and 2 during the middle jurassic phase the hfz was oblique to the extensional fault trends the reverse faults were reactivated as dextral strike slip faults as a result of transtensional inversion the inversion ratio of the hfz indicates an increase in deformational degree from east to west over the whole region the first deformation stage resulted from the n s compression between the south china and north china plates during the late triassic the second deformation stage of compression was related to the west northwestward subduction of the paleo pacific plate during the middle jurassic in the jurassic deformation framework the hfz may be interpreted as an accommodation structure parallel to the yanshan yinshan orogenic belt developed in the northern ordos area

mesozoic felsic arc magmatism and continental olivine tholeiites in zhejiang province and their relationship with the tectonic activity in southeastern china abstract the mesozoic geology of zhejiang province in southeastern china is characterized by two distinct geodynamic settings separated by a major tectonic event during the late jurassic early cretaceous a continental magmatic arc developed with a westward subduction of the kula or izanagi plate under the south china block during the development of this magmatic arc microsyenite porphyries and quartz bearing porphyries were emplaced in western zhejiang about 124 ma ago these porphyritic rocks intruded felsic tuffs that rest unconformably on carboniferous and permian folded strata geochemically they are enriched in lil and light rare earth elements lree which are features of acid shoshonitic suites isotopically they are characterized by negative nd t 124 5 3 to 4 7 values and high initial 87 sr 86 sr ratios 0 7079 0 7084 later in eastern zhejiang quartz phyric ignimbrites and subordinate acid andesites were emplaced and intruded by nearly contemporaneous microsyenitic and rhyolitic domes during the cretaceous about 97 ma ago all these rocks belong to the high k calc alkaline suites they show geochemical features of volcanic arc granites emplaced in an active continental margin and are characterized by negative nd t 97 8 8 to 7 1 and high initial sr isotopic ratios 0 7081 0 7089 the negative nd t 97 values of all the cretaceous calc alkaline and shoshonitic rocks of intermediate to acid composition suggest that these rocks were probably derived from a mantle wedge source contaminated by variable amounts of old crustal components likely represented by the proterozoic basement rocks of the south china block the contemporaneous igneous rocks in vietnam as well as in the fujian and guangdong provinces china represent the lateral counterparts of the zhejiang calc alkaline plutonic and volcanic rocks in the late early cretaceous an important tectonic event occurred which provoked the ending of the inagazi or kula plate subduction and affected the continental magmatic arc this tectonic event is likely related to the collision of the china indochina margin with the west philippine block after this tectonic event in the beginning of the late cretaceous continental stretching and crustal attenuation affected the south china block leading to the development of ne sw faulted basins in which continental olivine tholeiites and minor alkaline rhyolites were erupted both characterized by low nd t 97 ratios ca 4 meanwhile continental conglomerates and sandstones were also deposited this rifting process began likely before the india asia indentation and lasted at least until the late tertiary

new insight into a subduction related orogen a reappraisal of the geotectonic framework and evolution of the japanese islands abstract the geotectonic framework and the evolutionary history of the japanese islands need revision in accordance with the various geophysical geological evidence gathered by new methodologies in the recent years including seismic tomography vibroseis ground breaking seismic experiments and detrital zircon chronology these investigations have addressed various themes such as 1 seismic profile of the crust and mantle beneath the japanese islands 2 high precision ages of the protoliths of high p t metamorphic rocks and 3 provenance of terrigenous clastics the results have led to a number of important findings including 1 detection of a large mass of slab around the mantle boundary layer suggesting the long term oceanic subduction beneath japan 2 confirmation of the subhorizontal piled nappe structure for the entire crust of japan 3 finding a new high p t metamorphosed accretionary complex unit that represents the youngest blueschist in japan 4 finding of the oldest early cambrian arc batholith and cover sediments and 5 the identification of plural arc batholiths which have already been erased from the surface based on a synthesis of these new data this article presents a re evaluation of the conventional geotectonic subdivision of the subduction related orogen in japan re definition of the elements and their mutual boundaries and re consideration of the geotectonic evolution of the japanese islands in particular the historical change in provenance suggests that proto japan has experienced large scale tectonic erosion in multiple stages and the corresponding large amounts of continental crust materials were subducted for understanding the orogenic growth of japan during the last ca 500 million years the significance of tectonic erosion coupled with continental contraction as well as the oceanward accretionary growth requires further attention

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

transport through unimak pass alaska we examined inflow through unimak pass 200 m deep which is the only major connection between the shelves of the north pacific ocean and the eastern bering sea geostrophic transport was generally northward from the gulf of alaska into the bering sea the flow through the pass appeared to be modulated by the seasonal cycle of freshwater discharge on shorter time scales transport also was affected by semi daily variations in tidal mixing this effect was significant and not anticipated near bottom currents measured from moorings were maximum during winter and significantly correlated r 0 7 with the alongshore winds although the flow through unimak pass transported some nutrients from the north pacific ocean the gulf of alaska shelf is not the major source of nutrients to the bering sea shelf

observations of topographic planetary waves in the bering slope current using the geosat altimeter topographic planetary waves associated with the downstream leg of the bering slope current are observed in measurements of sea surface height anomalies acquired by the geosat altimeter during 1987 and 1988 the waves are most prominent from may to august 1987 during which time the estimated wave period and wavelength are about 72 days and 103 km respectively the direction of propagation is roughly north northeast

aleutian basin of the bering sea thermohaline oxygen nutrient and current structure in july 1993 an overview is given of the surface to bottom thermohaline oxygen nutrient and baroclinic flow structures in the aleutian basin of the bering sea and the adjacent north pacific based on high resolution field measurements in july 1993 a basic four layer vertical structure is observed in the upper 1500 m the 30 m top layer is warm low in salinity and nutrients and high in oxygen beneath it a 100 to 150 m thick temperature minimum layer is found believed to be a remnant of winter convection this is followed by a 300 m thick warm layer in which the main halocline oxycline and nutricline are located below it lies a layer of minimum oxygens and maximum nitrates and phosphates centered at a depth of 900 m in the bering sea but rising to 400 m south of the aleutians this basic structure is disrupted in the vicinity of amchitka pass due to strong tidal mixing the deep and abyssal waters of the aleutian basin differ substantially from those at comparable depth in the adjacent pacific by being warmer 0 1 c less saline 0 01 less dense 0 01 kg m3 poorer in oxygen 50 mol kg and richer in silicates 80 mol kg nitrates 1 0 mol kg and phosphates 0 3 mol kg the highest silicate concentrations 240 mol kg occur at the foot of the bering shelf unusual hydrographic conditions exist in an isolated tidal mixing basin in amchitka pass where the bottom mixed layer is 600 m thick 0 7 c warmer 0 14 less saline and 21 mol kg less oxygenated than at comparable depths outside baroclinic currents indicate strong deep jetlike flows on both sides of the aleutian ridge weak shallow eddies in the middle of the aleutian basin and somehat enhanced flows near the bering shelf edge the alaska stream in july 1993 was 100 km wide had a double core with a top speed of 0 54 m s and had a westward volume transport of 38 sv with 14 sv below 1000 dbar the north aleutian current had a speed of 0 2 m s and an eastward transport of 10 sv with 4 sv below 1000 dbar off the bering slope both eastward and westward flows were observed with volume transports near 7 sv

on the processes controlling shelf basin exchange and outer shelf dynamics in the bering sea abstract we use a 9 km pan arctic ice ocean model to better understand the circulation and exchanges in the bering sea particularly near the shelf break this region has historically been undersampled for physical chemical and biological properties very little is known about how water from the deep basin reaches the large shallow bering sea shelf to address this we examine here the relationship between the bering slope current and exchange across the shelf break and resulting mass and property fluxes onto the shelf this understanding is critical to gain insight into the effects that the bering sea has on the arctic ocean especially in regard to recent indications of a warming climate in this region the bering sea shelf break region is characterized by the northwestward flowing bering slope current previously it was thought that once this current neared the siberian coast a portion of it made a sharp turn northward and encircled the gulf of anadyr in an anticyclonic fashion our model results indicate a significantly different circulation scheme whereby water from the deep basin is periodically moved northward onto the shelf by mesoscale processes along the shelf break canyons along the shelf break appear to be more prone to eddy activity and therefore are associated with higher rates of on shelf transport the horizontal resolution configured in this model now allows for the representation of eddies with diameters greater than 36 km however we are unable to resolve the smaller eddies

inversion and propagation of the late paleozoic porjianghaizi fault north ordos basin china controls on sedimentation and gas accumulations abstract in contrast to typical intracratonic basins the ordos basin comprises marginal deformation belts and complex fault systems this study uses 3d seismic data tied to sonic and stratigraphic data from exploration wells to document the geographic extend of the porjianghaizi fault and its control on sedimentation and gas accumulation in the northern ordos basin our results show that the geometry of large porjianghaizi fault is controlled by five small fault segments the growth history of the porjianghaizi fault composes four stages 1 an initiation stage late carboniferous to early permian 2 a reactivation stage during the late triassic 3 an inversion stage during the middle jurassic and 4 an interaction and linkage stage during the late jurassic detailed studies show that the porjianghaizi fault had significant control on sedimentation and gas accumulation during the initiation stage late carboniferous to early permian five fault segments and associated relay ramps controlled the sedimentation in the study area the relay ramps formed transport pathways in which sediment extended from north basin margin to the basin center in contrast sedimentation along the fault was more localized based on shale gouge ratios sgr and formation water salinity the fault sealing capacity of the porjianghaizi fault is characterised by horizontal segmentation which means the fault composes laterally sealed areas and laterally connected areas along the fault strike as a corollary we propose that gas resources were mainly generated from the south where there are thick source rocks migrating vertically through interbedded open fractures first and then laterally through the junction zone of fault relay ramps it eventually accumulated in structural traps found in the northern areas understanding the evolution of the porjianghaizi fault is important for predicting the distribution of sedimentary facies in upper carboniferous and lower permian units as well as understanding the migration and distribution of gas resources in the north ordos basin these results can further help in hydrocarbon exploration in the north ordos basin

sedimentary record of triassic intraplate extension in north china evidence from the nonmarine nw ordos basin helan shan and zhuozi shan abstract the helan shan and zhuozi shan of the nw ordos basin china contain thick up to 4 km sequences of nonmarine triassic strata these rocks represent a major intraplate sedimentary basin the paleogeography tectonic setting and provenance of which are poorly understood and controversial studies of the sedimentary geology of the basin supported by new palinspastic reconstruction of younger deformation demonstrate that the basin filled from three sides by fluvial lacustrine deltaic and alluvial fan depositional systems the basin forms a westward thickening wedge that reaches its maximum thickness along the western margin of the helan shan and thins to a relatively constant 600 800 m east of the zhuozi shan the stratigraphy of the basin is strongly asymmetric alluvial fan strata are restricted to the extreme western margin of the basin and interfinger with axial fluvial deposits low in the section and deep lacustrine facies high in the section much of the eastern part of the basin is dominated by west flowing meandering river and deltaic systems large structures of triassic age have not been identified in the helan shan or zhuozi shan but small triassic normal faults have been documented in the western and central helan shan these characteristics most strongly support an extensional origin for the triassic basin in nw ordos the basin is interpreted to have been a north trending half graben bound along its western margin by an east dipping normal fault presently concealed beneath quaternary cover west of the helan shan the eastern margin now found in the zhuozi shan has simple ramp margin geometry driving mechanisms for this extension are not obvious due to limited documentation of triassic structure throughout the region but probably relate to far field stresses from the qinling or jinsha active margins interacting with the stable ordos block

upper paleozoic petroleum system ordos basin china abstract the ordos basin is a typical lapped basin including three sequences of strata early paleozoic late paleozoic and mesozoic with a total thickness of 4000 6000 m impermeable sealing beds are well developed at the top and base of the upper paleozoic sequence separating it from the mesozoic and the lower paleozoic strata to form an independent petroleum system in this petroleum system the source rocks are widely distributed coals and dark mudstones occurring in the carboniferous lower permian coal measures with a thickness of 10 15 and 40 60 m respectively the reservoirs are mainly early permian tight sandstones mostly with a porosity of 4 8 and a permeability of 0 1 1 0 10 3 m2 the regional cap rock is a 100 150 m thick mudstone in the upper permian strata the structural framework of the basin is a huge asymmetric syncline dipping gently toward the east and north and steeply toward the south and west well data show that gas saturated gas water transition and water saturated zones are developed from the depositional center to the basin edges the gas saturated zone mainly lies in the gently dipping slope area of the shanbei slope toward eastern and northern up dip directions the water gas transitional zone occurs and finally the water saturated zone presenting a reverse relation of water on top of gas an abnormal negative strata pressure is developed in the gas bearing area with a pressure coefficient cp ranging from 0 83 to 0 95 fluid inclusion data indicate that the upper paleozoic gas pool began to develop around the wuqi area at about 150 ma and it extended toward the north and was largely formed at about 120 ma showing there was a regional migration of the gas water interface from south to north during the gas pool formation these characteristics appear to show that the northern and eastern margins of the petroleum system are defined by a regional hydrodynamic regime the critical moment of the petroleum system occurred during the early cretaceous the basin experienced a rapid subsidence and a significant geothermal event resulting in the source rocks being matured into the main stage of gas generation to form a huge amount of gas the gas migrated into the tight sandstone reservoirs and displaced the rock pore water to form the gas pools and developing the regional hydrodynamic trap

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

palaeoproterozoic assembly of the north china craton the basement of the north china craton consists of the eastern and western blocks separated by the central zone both the eastern and western blocks are dominated by late archaean tonalitic trondhjemitic granodioritic gneiss complexes interdigitated with minor supracrustal rocks metamorphosed at 2 5 ga with anticlockwise p t paths the central zone is composed of reworked late archaean components and palaeoproterozoic juvenile crustal materials that underwent regional metamorphism at 1 85 ga with clockwise p t paths involving isothermal decompression as a result of collision between the eastern and western blocks which resulted in the final assembly of the north china craton

tidal currents in the st lawrence island region 1 vertical and spatial variability of tidal currents in the northern part of the bering sea near st lawrence island were examined using observations made at 17 new and historical current meter mooring locations the semidiurnal currents dominate over the diurnal currents semidiurnal currents exhibit a seasonal modulation with currents being somewhat stronger during the summer and fall when the density structure displays two layer stratification diurnal currents exhibit a weak semiannual modulation examination of the vertical structure of tidal currents shows that maximum semidiurnal currents are observed in the upper or middle layers down to a depth of about 20 m and below this depth the energy of the semidiurnal currents decreases rapidly however the energy of diurnal band currents remains almost constant with depth decreasing only in close proximity to the bottom rotary spectral analysis applied to the records shows further differences the m2 clockwise cw component of rotation dominates in the upper and middle water column but the counterclockwise component ccw dominates near the bottom interpretation of these observed results points to the different bottom boundary layers bbl for the cw and ccw motions in addition to the role of density stratification in organizing the bbl we compare results of a vertically averaged two dimensional model to the observationally derived tidal ellipse parameters and show that the barotropic formulation provides a first order description of the tidal regime within the domain

ocean circulation and exchanges through the northern bering sea 1979 2001 model results abstract we have developed and run a model with sufficiently high resolution 9 km and 45 levels and a large enough spatial domain to allow for realistic representation of flow through the narrow and shallow straits in the northern bering sea this is potentially important for quantification of long term mean and time dependent ocean circulation and water mass and property exchanges between the pacific and arctic oceans over a 23 year interval 1979 2001 mean transport through bering strait is estimated to be 0 65 sv comparison of our model results with published observations indicates that ocean circulation is not only variable at seasonal to interdecadal scales but it is also responsive to short term atmospheric forcing one of such events occurred during the winter of 2000 2001 with reversed oceanic flow in some areas and much reduced sea ice cover analyses of eddy kinetic energy fields identify some high biological productivity regions of the chirikov basin coincident with persistent high energy up to 2700 cm 2 s 2 in the surface layer and up to 2600 cm 2 s 2 at mid depth throughout the annual cycle model output in the bering strait region is validated against several time series of moored observations of water mass properties comparison with shipboard observations of near bottom salinity from late winter through autumn indicates that the model reasonably represents the major water mass properties in the region the modeled vertical water column structure in the northern bering sea allows increased understanding of the mechanisms of water transformation and transport northward through bering strait into the chukchi and beaufort seas we conclude that the long term model results for the northern bering sea provide important insights into the ocean circulation and fluxes and they are a useful frame of reference for limited observations that are short term and or cover only a small geographic region

northward flow in the bering and chukchi seas the ocean circulation on the bering and chukchi sea shelves is investigated using a barotropic numerical model in the presence of the winter seasonal wind stress from the northeast observed northward transport through bering strait of 0 6 sv for the 8 month winter season 1981 1982 can be driven by a sea level difference of 0 4 m between the pacific and arctic oceans this sea level difference between basins is in agreement with hydrographic estimates in the absence of wind stress a 0 4 m sea level difference drives a northward transport through bering strait of 1 1 sv maximum transport through bering strait is geostrophically limited not frictionally or inertially limited major qualitative circulation features of the region are evident in the simulations westward intensification of the northward transport across the bering sea shelf is confirmed with the major transport occurring in the relatively deep gulf of anadyr in the absence of wind anadyr strait contributes 72 of the northward transport through bering strait with northeasterly winds there is a net clockwise circulation around saint lawrence island within the 20 m isobath norton and kotzebue sounds are little influenced by the general circulation northward transport in the chukchi sea bifurcates in the vicinity of point hope the predominant branch is directed toward the northwest in a broad canyon feature south of herald shoal and the balance becomes the alaskan coastal current between cape lisburne and point barrow

characteristics of currents over the continental slope of the eastern bering sea between september 1989 and 1990 twenty six current records were collected by instruments on eight moorings located in pribilof and zhemchug canyons and at a site midway between these features these records provide the first long term eulerian measurements from the slope and mid slope of the eastern bering sea results from the current records together with water property observations permit a characterization of the bering slope current moderate flow 2 to 18 cm s 1 followed the bathymetry toward the northwest and existed primarily in the upper 300 m wind and current energy increased in winter but vector mean current did not increase at all sites wind forcing accounted for only a small fraction of the current fluctuations at one mid slope location in pribilof canyon bathymetry resulted in rectification of the strong daily tidal current estimates of heat and salt fluxes indicate some significant shoreward transport however this flux did not occur preferentially in the canyons

paleogeography reconstruction of a multi stage modified intra cratonic basin a case study from the jurassic ordos basin western north china craton abstract post depositional modification is commonly found in sedimentary basins particularly in the eastern tethys tectonic domain and is related to special geological settings and evolution processes of the region the chinese continent is composed of numerous small scale blocks that underwent intensive tectonic movements paleogeography reconstruction for a modified basin is fundamental for objectively understanding the basin dynamics and exploration of hydrocarbon sandstone type uranium deposits and other mineral resources as a large scale intra cratonic depression basin in the western part of the north china craton ncc the mesozoic ordos basin underwent multi stage modification as a result only the western part was preserved in this study the paleogeography in bathonian oxfordian ages of the jurassic was reconstructed via integrated approaches including stratigraphic correlation sedimentary facies analysis provenance analysis and fission track analysis the original sedimentary boundary of the ordos basin during this period is approximately outlined we determine that the northern and southern borders reach the cenozoic hetao basin and the cenozoic weihe basin respectively and that the eastern northwestern and southwestern borders lie to the west of taihang mountain at the langshan bayanhot basin kexueshan and to the west of liupan mountain respectively the original sedimentary extent of the ordos basin was almost twice that of the present day residual basin the evolution of this basin in the mesozoic recorded the evolution and destruction processes of the ncc the ncc shows that n s and w e trending compressional setting occurred during the triassic and the jurassic respectively the interactive activities of adjacent tectonic domains played a critical role in subsidence dynamics for the intra cratonic ordos basin this study provides further insights for exploration of hydrocarbon and sandstone type uranium deposits in the ordos basin

is the jurassic yanshanian intraplate tectonics of north china due to westward indentation of the north china block terra nova 24 333 338 2012 abstract the northern mountains of beijing are the type locality of the mesozoic yanshanian orogen our structural study emphasizes the importance of dextral strike slip for the formation of this intracontinental belt the south and north directed thrusts are positive flower structures rooted in strike slip faults this transpressional tectonics developed from late triassic to late jurassic early cretaceous through three deformation phases coeval with syntectonic sedimentation separated by two transtensional episodes coeval with magmatism the late jurassic early cretaceous tectonic event is also recognized in several places of north china strike slip faulting controls the deformation of the northern border of the north china block in the yanshan yinshan belt simultaneously east directed thrusts and folds develop along n s elongated ranges in helanshan shanxi highlands and taihangshan the jurassic tectonics of the north china block is interpreted in a unitary way as the result of the westward underthrusting of the north china block below the alashan block

circulation in the bering sea 1982 83 based on satellite tracked drifter observations abstract a satellite tracked drifting buoy deployed unintentionally in the bering sea in 1982 completed a circuit of that basin in about one year during its cyclonic passage around the bering sea it experienced many different flow regimes ranging from steady alongshelf motion at the shelf break to highly variable tidal flow on the shelf itself the buoy trajectory differs from previous descriptions of the deep bering sea circulation because it moved southwestward in the central bering sea rather than along the western boundary as other depictions have suggested many of the bering sea mesoscale eddies reported earlier were evident indicating that possibly these eddies are permanent features the forces which caused the buoy to move between the various flow regimes are unclear but the data suggest an annual period for the deep bering sea circulation

hydrothermal mineralization in the sandstone hosted hangjinqi uranium deposit north ordos basin china abstract tabular type uranium ore deposits the hangjinqi and daying deposits have recently been found in the middle jurassic zhiluo formation north of the ordos basin china petrographic observations the chemical composition of u minerals determined by empa and fs la icp ms whole rock geochemistry and the microthermometric study of fluid inclusions have been integrated to characterize the genetic conditions of the u mineralization in the hangjinqi sandstone hosted deposit two different groups of u minerals have been identified one group includes coffinite i associated with vanadium rich micas coffinite i is enriched in vanadium v and devoid of iron fe and yttrium y and has a lree enriched chondrite normalized ree pattern the u minerals of this group are similar to meteoric fluid infiltration related deposits the second group has coeval coffinite ii and coarsely crystalline calcite cement coffinite ii is enriched in y and fe and depleted in v and is marked by a flat chondrite normalized ree pattern which is compatible with typical hydrothermal genetic deposits with high salinity mineralizing fluids the temperature and salinity of the primary aqueous inclusions in the ore stage calcite are 120 180 c and 8 00 16 34 eq wt nacl respectively these mineral assemblages temperatures and salinities indicate that the hangjinqi deposit was affected by two distinct types of ore bearing fluids low salinity meteoric waters and high salinity hydrothermal fluids the meteoric fluids event began at 97 5 ma with the titling of the northern ordos basin and the uplift of the hetao region to the north hydrothermal u mineralization occurred since 39 2 ma with the rifting of the hetao graben thus the previous biogenic model for the u mineralization should be modified in the uraniferous region of the north ordos basin

variability of physical and chemical characteristics along the 70 m isobath of the southeastern bering sea abstract from observations of ice cover temperature salinity currents and nitrate it is evident that along shelf variability was significant over the middle shelf of the eastern bering sea but less distinct than that observed in the cross shelf domains along the 70 m isobath three zones were evident in the summer the southeastern cold pool centered at 57 n an intermediate zone consisting of warmer water with weaker stratification and the northern cold pool extending northward from 58 n small scale 20 km horizontal features that persisted for months were common nutrient concentrations were related to salinity and were replenished more uniformly over the southern shelf than north of the pribilof islands although mean currents were weak 1 cm s 1 short energetic advective events impacted the temperature and salinity structure

geophysical and geological tests of tectonic models of the north china craton abstract the geometry and timing of amalgamation of the north china craton have been controversial with three main models offering significantly different interpretations of regional structure geochronology and geological relationships one model suggests that the eastern and western blocks of the ncc formed separately in the archean and an active margin was developed on the eastern block between 2 5 and 1 85 ga when the two blocks collided above an east dipping subduction zone a second presumes the eastern block rifted from an unknown larger continent at circa 2 7 ga and experienced a collision with an arc perhaps attached to the western block above a west dipping subduction zone at 2 5 ga and the 1 85 ga metamorphism is related to a collision along the northern margin of the craton when the ncc joined the columbia supercontinent a third model suggests two collisions in the central orogenic belt at 2 1 and 1 88 ga but recognizes an early undated deformation event recent seismic results reveal details of the deep crustal and lithospheric structure that support both the second and third models showing that subduction beneath the central orogenic belt was west directed and that there is a second west dipping paleosubduction zone located to the east of the cob dipping beneath the western block ordos craton the boundaries identified through geophysics do not correlate with the boundaries of the trans north china orogen suggested in the first model and the subduction polarity is opposite that predicted by that model high pressure granulite facies metamorphism at 1 85 ga is not restricted to the tnco as suggested by the first model but is documented across the ncc as predicted by the second model suggesting a major continent continent collision along the north margin of the craton at 1 85 ga further it has recently been shown that in the southern tnco there is no record of metamorphism at circa 1 85 ga but only at 2 7 2 5 ga showing that the tnco as defined as a circa 1 85 ga orogen does not exist this is further confirmed by recent re os isotopic studies which show that the subcontinental lithospheric mantle beneath the southern cob is late archean in age and that a province in the northern ncc is circa 1 8 ga correlating with the proposed collision belt of the ncc with the columbia supercontinent across the entire ncc the cob is an archean convergent belt re worked in the paleoproterozoic and the paleoproterozoic tectonism is widespread across the ncc as predicted by the model whereby the previously amalgamated eastern and western blocks experienced a continental collision with columbia at circa 1 85 ga but uplift exhumation rates are slow necessitating a re evaluation of the tectonic models of the ncc

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

mesozoic northeast qaidam basin response to contractional reactivation of the qilian shan and implications for the extent of mesozoic intracontinental deformation in central asia

evolution and origins of pyrite in sandstone type uranium deposits northern ordos basin north central china based on micromorphological and compositional analysis abstract pyrite is an abundant mineral throughout the uranium bearing middle jurassic zhiluo formation northern ordos basin three different morphologies of pyrite are identified framboidal euhedral and cement based on textural and geochemical results from optical microscopy secondary electron se and back scattered electron bse imaging energy dispersive spectroscopy eds electron probe microanalysis epma and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icpms three evolutionary models are proposed as follows aggregation of framboids to form polyframboids as a result of the bacterial sulfate reduction bsr processes the formation of cement pyrite under the addition of thermal fluids with numerous framboids and microcrystals inside and euhedral pyrite evolving from framboids the analytical data show that there is a minor increase in major and trace element contents in transformed pyrite and each pyrite morphology has a distinct sulfur isotopic composition 9 9 to 8 0 for framboids 19 1 to 14 2 for polyframboids 18 7 to 20 3 for euhedral pyrite and 15 7 to 21 2 for cement pyrite this indicates that the sulfur was derived from more than one source compared with the original framboids the association between uranium and different types of pyrite indicates that different processes e g bsr and thermogenic sulfate reduction tsr were involved in the precipitation of uranium mineralization and are important to the formation of the precipitation of uranium in the zhiluo formation northern ordos basin

geochemical study of crude oils from the xifeng oilfield of the ordos basin china abstract the xifeng oilfield is the largest newly discovered oilfield in the ordos basin in order to determine the possible source crude oils collected systematically from the oilfield and an adjacent oilfield have been examined isotopically and molecularly the predominance of long chain n alkanes high abundance of c29 sterane lower ratios of c25 c26 tricyclic terpane and c25 tricyclic terpane c24 tetracyclic terpane and high c24 tetracyclic terpane c24 tetracyclic terpane c26 tricyclic terpanes ratio in the studied oils suggest generation from a source with mixed terrigenous and algal bacterial organic matter the presence of diterpenoid hydrocarbon with abietane skeletons is characteristic of the main contribution of higher land plants to the oils the biomarker distributions in the oils show that they were formed under a weakly reducing freshwater environment molecular maturity parameters indicate that the crude oils are mature the oil source rock correlation and oil migration investigation suggest that the oils in the xifeng oilfield originated from the source rocks of the yanchang formation deposited in a shallow to deep freshwater lacustrine environment especially chang 7 source rocks the data from the distribution of pyrrolic nitrogen compounds indicate that the charging direction of the chang 8 crude oils is mainly from the zhuang 12 well northeast of the oilfield toward the southwest this direction of oil migration is consistent with that indicated by regional geological data

spatial and temporal characteristics of the wind forcing of the bering sea abstract the surface wind stress over the bering sea is estimated for the period 1946 90 from sea level pressure analyses empirical relationships between the geostrophic wind and the surface wind and a bulk aerodynamic formula the focus is on the propagation and variability of the stress and the curl of the stress as a function of frequency the stress at high frequencies 0 1 cpd is dominated by northward and eastward propagating disturbances with mean wavelengths of 2500 and 10 000 km respectively at periods of 10 100 days the mean propagation is near zero there are however significant interannual variations in the zonal propagation wind driven ocean transports estimated by the sverdrup method for the deep bering basin account for 6 sv or roughly one half of the observed transport within the western boundary current along the kamchatka peninsula a low pass filtered retaining periods greater than 18 months time series of the sverdrup transport exhibits a standard deviation of 25 of th

mesozoic contractional deformation in the middle of the asian tectonic collage the intraplate western ordos fold thrust belt china abstract intraplate deformation can occur at great distances from synchronous plate boundaries and is most likely the result of strain concentrations into weak zones these weak zones may be pre existing crustal heterogeneities such as faults thermally weakened zones due to magmatism and or the effects of a thick sedimentary cover or mechanical contrasts between adjacent crustal blocks intraplate deformation is not exclusively related to continent continent collision it can be the result of a change in subduction dynamics or the interaction of two convergent plate boundaries asia has many examples of active intraplate deformation that are thought to be related to the cenozoic indo asian collision although much attention is placed on active examples discerning controls on pre cenozoic asian intraplate deformation will lead to not only a better understanding of the processes involved in intraplate orogens but also the tectonic evolution of asia situated on either side of the yellow river along the western margin of the ordos plateau the intraplate western ordos fold thrust belt involves units as old as archean basement and as young as late jurassic the fold thrust belt is spectacularly exposed in two ranges the helan shan and the zhuozi shan cross sections drawn through the north trending fold thrust belt suggest 30 minimum shortening a paleocurrent reversal within the lower middle jurassic section is interpreted to mark the onset of contraction and mountain building a late jurassic synorogenic boulder conglomerate records the final deformation in the fold thrust belt synchronous with contraction and cutting across the fold thrust belt is an e w striking strike slip fault that displays right lateral drag and sub horizontal striae we interpret this fault as an accommodation structure in the thrust belt following e w contraction the thrust belt was dismembered by an n15 w trending left lateral strike slip fault the left lateral fault displaces the frontal portion of the thrust belt the zhuozi shan 62 km to the north relative to a more internal portion the helan shan we propose that the anomalous orientation and intraplate location of the western ordos fold thrust belt is a function of mechanical contrasts between a previously deformed area and a stable crustal block ordos to the east pre existing crustal weakness or anisotropy along the western margin of the ordos block is most likely related to either a late proterozoic early paleozoic aulacogen a triassic fault system or to both although its intraplate location and the complexities of mesozoic asian plate interactions make it difficult to relate deformation in the western ordos fold thrust belt to a specific contemporaneous plate boundary its n s trend may suggest a link with paleo pacific subduction along the eastern margin of asia

some controls on flow and salinity in bering strait 1 during 1993 1994 steric forcing of flow through bering strait represented a northward sea level drop of 0 7 m from the bering sea basin to the adjacent deep arctic ocean of which 2 3 was due to the salinity difference between the basins seasonal variability of steric forcing appears small 0 05 m in contrast to large seasonal wind effects interannual changes in steric forcing may exceed 20 however and warm inflow from the north atlantic accumulation of freshwater in the southwest canada basin and temperature and salinity changes in the upper bering sea have all contributed to recent changes the mean salinity balance in bering strait is primarily maintained by large runoff to the bering shelf dilute coastal inflow from the gulf of alaska and on shelf movement of saline and nutrient rich oceanic waters from the bering sea basin in bering strait therefore both the throughflow and its salinity are affected by remote events

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed