directional borehole logging configurations using dc and telluric methods for detecting deep conductors not intersected by wells herewith two borehole directional geoelectrical configurations have been introduced for the detection of deep conductors not intersected by the well the first one is a hole to surface configuration hsc using the dc current and the second one is a telluric configuration tc characterized by a deeper penetration depth and a directional effect both configurations have superiority comparable with other traditional geoelectrical configurations basically a directional natural induced polarization methodology termed dnip has been developed and proposed by benefiting from borehole telluric measurements taken at two sufficiently low frequencies these configurations have been tested in the rouez mine bretagne france where sulphide mineralization is known to occur several anomalies have been isolated in field data and interpreted by different interpretative techniques the results obtained by applying these configurations are in good agreement and the detected conductors are confirmed by morphological and lithological description

comparison of ground water flow model particle tracking results and isotopic data in the mojave river ground water basin southern california usa abstract flow path and time of travel results for the mojave river ground water basin southern california calculated using the ground water flow model modflow and particle tracking model modpath were similar to flow path and time of travel interpretations derived from delta deuterium and carbon 14 data model and isotopic data both show short flow paths and young ground water ages throughout the floodplain aquifer along most the mojave river longer flow paths and older ground water ages as great as 10 000 years before present were measured and simulated in the floodplain aquifer near the mojave valley model and isotopic data also show movement of water between the floodplain and regional aquifer and subsequent discharge of water from the river to dry lakes in some areas it was not possible to simulate the isotopic composition of ground water in the regional aquifer away from the front of the san gabriel and san bernardino mountains because recharge in these areas does not occur under the present day climatic conditions used for calibration of the model

basin superposition on the northern margin of the south china sea abstract basin superposition on the northern margin of the south china sea is a product of pulsed basin development with geometries which changed through space and time of changing strain fields and of tectonically inherited pre existing zones of crustal weakness this region of the south china sea was welded together or assembled prior to the cretaceous three distinct episodes of continental disassembly and accompanying basin evolution ensued each episode commencing with rifting and the formation of grabens or half grabens and each terminating with a gentle subsidence phase the major trends of the faults and basins varied from predominantly ne for the first episode through ne ew for the second to ew nw for the third the first episode occurred during the late cretaceous to paleocene as a back arc extensional domain induced by the dip steepening of a subducted oceanic slab the second basin episode of the late eocene to early oligocene was initiated by the collision of the indian plate with the eurasian plate the continued penetration of the former into the latter led to the tectonic escape and subsequent clockwise rotation of the indochina block creating regional transtension and left lateral motion along the red river fault the third episode of basin development occurred during the middle miocene as a reactivated product of this collision owing to the clockwise rotation of indochina the approximately e w trend of the simple shear principal displacement zone changed to northwest by the pliocene the eastward extrusion of south china had exceeded that of indochina reversing the sense of red river fault displacement to right lateral a clockwise rotation of the red river geosuture together with considerations of the influence of zones of inherited crustal weakness provides a model for the observed episodic changes in regional strain such a model best explains the post cretaceous evolution of superimposed basins on the northern margin of the south china sea

rifting process of the xihu depression east china sea basin abstract having a maximum depositional depth up to 15 km the ne trending xihu depression is evolved from a deep paleogene continental margin rifting along the present day east china sea continental shelf in this paper we use deep seismic reflection well logging and gravity data to synthesize early rifting process of the depression to study the regional tectonic subsidence history we developed a computer program that performs backstripping and simultaneous inversion for stretching factor initial lithospheric thickness and incipient age of thermal subsidence tectonic subsidence analyses of 40 industrial wells reveal nonuniform stretching preferential crustal extension along the depocenter but preferential mantle extension at the western flank uniform extension may have occurred only somewhere between the central inversion zone and the western margin in the early rifting stage subdued initial subsidence or initial uplift is observed on several wells near the western margin due possibly to flexural isostatic balance the initial mechanical lithospheric thicknesses from subsidence inversion seem to vary from about 55 km to almost 130 km suggesting significant longitudinal segmentation as well as transverse variation in the prerifting lithosphere it is likely that the southern part of the xihu depression was developed initially on a region of relatively thin lithosphere a statement conformable to geological evidences nw se trending deep seismic profiling clearly reveals the deep basement structure of the depression as well as the synrift and postrift sedimentary packages separated by a breakup unconformity crustal layer thicknesses are independently estimated from gravity modeling inversion tectonic subsidence analyses and deep seismic profiling respectively these methods all arrive at very small present day thicknesses of the crustal layer beneath the depocenter of the xihu depression

back arc rifting in the okinawa trough abstract geological and geophysical data reveal that the okinawa trough shows incipient continental rifting and crustal separation started from about 2 ma the early extensional movements in the trough are probably of miocene age in addition to the miocene phase two main periods of extension are recognized a pleistocene phase between 1 9 and 0 5 ma and the present day phase during the stage short central rifts central grabens were formed the opening however may have occurred only in the southern part of the trough basin having an average half spreading rate of 2 cm yr 1 since early pleistocene time producing its present width of several tens of kilometres these activities were well represented by igneous intrusions sedimentary facies and sedimentary structures in and around the okinawa trough the width of the zone affected by back arc extension defined as greater okinawa trough is larger than the present okinawa trough whose width is 200 250 km the present form of the greater okinawa trough started to form at the same time as that of the okinawa trough

full fit reconstruction of the south china sea conjugate margins although the south china sea margins have been well studied there are no full fit reconstructions that document the complex rifting history in a regional geodynamic context we restored conjugate margins to their original late cretaceous unstretched geometries and generated the first full fit reconstructions of the south china sea conjugate margins the impact of magmatic underplating on restoration and full fit reconstruction was estimated quantitatively the full fit reconstruction model includes restoration uncertainties and results in minimum gaps and overlaps between the restored conjugate margin geometries based on our restoration the full fit reconstruction and the continental basement thickness distribution we estimate that there was more extension of continental basement on the western part of the conjugate margins compared with the eastern margin prior to the initiation of seafloor spreading therefore the mid ocean ridge initially formed in the east and propagated westward to open the south china sea seafloor spreading propagated along the xisha trough during nw sub basin formation but continental breakup occurred along the southern side of the zhongsha xisha islands where the lithosphere was probably weaker than along the xisha trough consistent with the geometry and evolution of the nw sub basin and the southward jump of the mid oceanic ridge c 2015 elsevier b v all rights reserved

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

on sensitivity of surface to borehole resistivity measurements to the attitude and the depth to center of a three dimensional spheroid borehole to surface and surface to borehole resistivity measurements are versatile but not totally tested methods for detecting anomalies in the vicinity of a borehole the former method has been discussed by several authors alfano 1962 merkel 1971 merkel and alexander 1971 barnett 1972 snyder and merkel 1973 snyder 1976 daniels 1977 1978 and 1983 but the latter has not received much attention morrison 1971 and daniels 1977 are among the few who have addressed the problem each method has its own advantages surface to borehole resistivity measurements are made by placing a current source on the surface and measuring the apparent resistivity in a borehole in which the measuring electrodes are closer to the body than in the borehole to surface case pilot studies presented here suggest that the surface to borehole method can provide indicators of the attitude and the depth to the center of a body this paper illustrates a simple method for qualitatively determining the attitude and t

an inverse method of modeling thermal histories from apatite fission track data abstract apatite fission track ft ages and track length distributions are important sources of information about the thermal histories of rocks recent advances in the understanding of track annealing in apatite provide a solution to the forward problem of predicting ft ages and track length distributions that result from a given thermal history in this paper a method is presented to address the inverse problem estimation of the thermal history from ft data the inverse method uses an iterative approach the downhill simplex to systematically modify a starting thermal history to achieve satisfactory statistical agreement between the predicted and observed ft age and track length distribution however because of analytical uncertainties a unique thermal history does not exist monte carlo simulations are used to take into account the uncertainties in the data and yield a spectrum of possible thermal histories the results are based on the isothermal annealing model of laslett et al 1 chem geol isot geosci sect vol 65 but because the method uses forward predictions and not an analytical formula specific to a single annealing model alternative annealing models could be used within the same framework this method is an improvement in interpreting fission track data because the range of thermal histories permitted by the data can be evaluated to demonstrate the method it is applied to several sets of test data created by forward modeling of idealized thermal histories the results show that the age at which the sample cooled through its closure temperature and the most general features of the thermal history are revealed however data from partially annealed samples have wide spectra that reflect large uncertainties in the form of the thermal history for such samples ft data alone are not likely to provide strong tests of geologic hypotheses conversely geologic information may play a crucial role in constraining the thermal history spectrum in application to uplift related cooling this inverse method can provide much more realistic assessments of the cooling rate and its uncertainty than are otherwise possible

neogene subsidence pattern in the multi episodic extension systems insights from backstripping modelling of the okinawa trough abstract extensional systems of back arc basins have been widely recognized and studied in se asia however the interactions between extensional tectonics and spatial temporal distributions of tectonic subsidence in an active back arc basin are poorly known using a backstripping technique we analysed 33 multichannel seismic profiles to calculate the neogene tectonic subsidence across the entire okinawa trough ot for the first time reconstruction of the tectonic subsidence shows that the ot can be roughly divided into four subsidence stages with variable rate by comparing the temporal spatial distribution of the intensive subsidence area we confirmed that rifting events first occurred in the northern segment not and middle segment mot from the miocene to late pliocene and then propagated to the southern segment sot after the late pliocene the factors controlling the rapid tectonic subsidence over the entire ot can be classified into two categories 1 ne to nne trending normal faulting related to extension of the ot and nw to nww trending strike slip faulting i e the tokara fault and the miyako fault related to subduction of the philippine sea plate under the eurasian plate 2 the anomalous rapid subsidence occurred in the southernmost part of the sot is likely related to the subducted gagua ridge which caused magma intrusion resulting from partial melting we suggest that magmatic bodies produced by partial melting of subducted materials intruded into the crust and created a dense lithosphere causing this rapid tectonic subsidence

water movement through a thick unsaturated zone underlying an intermittent stream in the western mojave desert southern california usa previous studies indicated that small amounts of recharge occur as infiltration of intermittent streamflow in washes in the upper mojave river basin in the western mojave desert near victorville california these washes flow only a few days each year after large storms to reach the water table water must pass through an unsaturated zone that is more than 130 m thick results of this study done in 1994 1998 show that infiltration to depths below the root zone did not occur at control sites away from the wash at these sites volumetric water contents were as low as 0 01 and water potentials measured as the combination of solute and matric potentials using a water activity meter were as negative as 14 000 kpa water vapor movement was controlled by highly negative solute potentials associated with the accumulation of soluble salts in the unsaturated zone highly negative matric potentials above and below the zone of maximum solute accumulation result from movement of water vapor toward the highly negative solute potentials at that depth the 18o and d delta oxygen 18 and delta deuterium isotopic composition of water in coarse grained deposits plots along a rayleigh distillation line consistent with removal of water in coarse grained layers by vapor transport beneath oro grande wash water moved to depths below the root zone and presumably to the water table about 130 m below land surface underneath oro grande wash volumetric water contents were as high as 0 27 and water potentials measured as matric potential using tensiometers were between 1 8 and 50 kpa on the basis of tritium data water requires at least 180 260 years to infiltrate to the water table clay layers impede the downward movement of water seasonal changes in water vapor composition underneath the wash are consistent with the rapid infiltration of a small quantity of water to great depths and subsequent equilibration of vapor with water in the surrounding material it may be possible to supplement natural recharge from the wash with imported water recharge to the wash may be advantageous because the unsaturated zone is not as dry as most areas in the desert and concentrations of soluble salts are generally lower underneath the wash

present day heat flow thermal history and tectonic subsidence of the east china sea basin the east china sea basin is located in the convergence area between the eurasian plate the pacific plate and the philippine sea plate and consists of two depressions the taibei depression in the west and the xihu depression in the east heat flow measurements show that the east china sea basin is characterized by present day heat flow around 70 6 mw m 2 varying between 55 and 88 mw m 2 no significant difference in heat flow is observed between the xihu and the taibei depressions thermal history reconstruction using vitrinite reflectance suggests that the thermal history was however different in the taibei and the xihu depressions paleo heat flow values when the pretertiary formations experienced their maximum temperature at the end of the paleocene reached a mean of 82 mw m 2 in the taibei depression much higher than the present day value the lower tertiary sediments in the xihu depression experienced maximum temperatures at the end of oligocene 35 4 23 3 ma and reached a mean paleo heat flow value of 83 mw m 2 tectonic subsidence analysis shows that the timing of the major rifting episode was different across the east china sea basin the rifting occurred from the late cretaceous w65 ma to the early eocene w55 ma in the taibei depression followed by thermal subsidence from the late eocene to the end of miocene 23 3 5 2 ma in contrast in the xihu depression the initial subsidence lasted until the early miocene and thermal subsidence to the end of miocene from pliocene to the present an accelerated subsidence took place all along the west pacific margin of asia significant thicknesses of strata were removed from the unconformities in the basin the mean amount of erosion was 1147 m from the paleocene and 1208 m above the oligocene in the taibei depression and 1409 m from the oligocene in the xihu depression q 2004 elsevier ltd all rights reserved

cenozoic extensional tectonics in china abstract this paper gives a brief review of the cenozoic extensional structures of china during the cenozoic eastern china was in a rifted setting where divergent plate motion and extensional structures were dominant subsidence has occurred initially in response to attenuation of the crust and was enhanced later by subsidence due to thermal contraction in western china particularly in the qinghai tibetan plateau where rifting occurs in an orogenic setting in which convergent plate movements are dominant the rifting is associated with continental collision and lateral escape and large intra continental transform boundaries extensional structures in china may be grouped into eleven graben systems in eastern china and four in western china they occur in different styles linear rift valley basin and range structures and pull apart basins associated with strike slip faults the geometric characteristics kinematics of extension and the mechanism of continental extension in china are discussed the cenozoic extrusion structural model proposed by tapponnier et al 1982 elegantly accounts for the gross tectonics and the formation of the graben systems of western china however in considering the overall strain pattern during the extension of the early tertiary basin and range region in eastern china a large scale simple shear kinematic model may be preferable to the pure shear rift model

determination of paleoheat flux from vitrinite reflectance data a method is presented for determining paleoheat flux from the reflectance of vitrinite collected from wells the maturation of vitrinite is modeled using a time temperature integral that assumes pseudo first order kinetics in testing the numerical algorithm it was necessary to introduce a critical temperature of 295 k below which vitrinite does not mature this result is consistent with the latest findings of independent researchers the degree of consistency obtained from a number of wells is not perfect much of the inconsistency can be attributed to large uncertainties in the vitrinite reflectance readings to test the method heat flow history was determined for the north sea basin and the national petroleum reserve of alaska quantitative results were obtained detailing the increase and or decrease of heat flux with time and were consistent with the qualitative behavior inferred for paleoheat flow from current geologic models

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

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

timing of trap formation and petroleum generation in the northern east china sea shelf basin basin modeling and cross section restoration from the northern east china sea shelf basin reveal the timing of trap formation and petroleum generation cross section restoration suggest that extension started in the late cretaceous and was interrupted by inversion at the end of miocene that created large anticline structures providing numerous petroleum traps one dimensional basin modeling of the jdz vii i well show that the main phase of oil generation in the synrift fluvial shales in the jeju basin occurred during the early oligocene middle miocene period predating the regional inversion thus potential for large oil accumulations in the southern part of the basin is probably limited most of the petroleum are likely to have flowed toward the basin margin as well as basin center until the late miocene because no structures were available to capture them the formation of anticline structures overlapped and or postdated the main phase of gas generation in the jeju basin this is probably why the jdz vii 1 is gas prone with the gas trapped mainly in the anticlinal structures formed by the tectonic uplift the source rocks in the southwestern part of the domi basin are immature for petroleum generation

effect of burial history on diagenetic and reservoir forming process of the oligocene sandstone in xihu sag east china sea basin abstract porosity evolution history hydrocarbon charging periods diagenetic and reservoir forming characteristics of low permeability and tight sandstone are presented in this study the interpretation is based on information including thin section scanning electron microscope homogenization temperature of fluid inclusion bulk rock x ray diffraction analysis clay x ray diffraction analysis and stable isotopic composition these sandstones are located in the oligocene e3h formation in the xihu sag east china sea basin east china five diagenetic events in the h3 h4 and h5 members were determined including connate alkaline pore water of the oligocene sandstone meteoric water leaching in late miocene organic acids and co2 acidic fluids in early middle miocene reservoir temperature decrease induced by tectonic uplift and alkaline diagenetic environment from late miocene to present day porosity evolution history of different grain size lithology were evaluated by basin modelling and test data the medium sandstone and coarse sandstone of the h3 member and medium sandstone of the h4 member not reached the tight state in the geologic time the fine sandstone of the h4 member entered the tight state at 12 ma suffered acidic fluids to improve the tight state in late stage and entered the tight state again since 6 5 ma the medium sandstone fine sandstone and siltstone in the h5 member entered the tight state at 13 5ma 16ma and 19ma respectively three hydrocarbon charging periods were determined including 15 5 ma 10 4 ma in the middle miocene 9 6 ma 7 0 ma in the late miocene and 6 2 ma 0 0 ma from the late miocene to present day three diagenetic and reservoir forming patterns were proposed including accumulation without tightness accumulation after tightness improving reservoir quality with acidic fluid accumulation while tightness accumulation after tightness the burial history cannot be ignored in the diagenetic events porosity evolution history and hydrocarbon charging periods of similar low permeability and tight sandstone in sedimentary basins

the mesozoic cenozoic east china rift system abstract the mesozoic cenozoic rift system of eastern china extends in a n s direction over a distance of some 4000 km and has a width of 600 1000 km to the east it reaches into the coastal areas of the east and south china sea and extends onto the continental shelf this very large rift system evolved on a heterogenous basement consisting of a number of terranes which were amalgamated during the indosinian orogeny a first rifting phase spanned late jurassic early cretaceous times it was followed by a period of relative tectonic quiescence and thermal relaxation a latest cretaceous phase of compressional tectonics giving rise to partial basin inversion was followed by a renewed rifting cycle spanning eocene early neogene times development of the east china rift system involving vertical as well as lateral crustal movements was probably induced by physico chemical changes within the earth s mantle that can be related to activity along the pacific subduction zones the mesozoic cenozoic east china rifts contain some important hydrocarbon provinces which rely to a large extent on syn rift sediments for source and reservoir rocks

structural characteristics of the northern okinawa trough and adjacent areas from regional seismic reflection data geologic and tectonic implications abstract analysis of regional multi channel seismic data from the northern okinawa trough and adjacent shelf provides some important constraints on the structural development of the area the sedimentary strata in the northern east china sea shelf basin separated from the okinawa trough by the taiwan sinzi belt are affected by the miocene compressional tectonism and truncated by the late miocene unconformity in contrast those in the western margin of the northern okinawa trough are cut by numerous normal faults and the late miocene horizon forms a conformable surface this suggests that the taiwan sinzi belt acted as a buttress for the northern okinawa trough against the compressional tectonism our data also reveal the ho basin in the western margin of the northern okinawa trough previously known only from proprietary industry data the longwan ridge lying between the ho basin and the northern okinawa trough may be the youngest of the relict arcs or buried ridges in the area the abrupt along strike change in the fault polarity near the northern margin of the depocenter of the ho basin suggests a nw trending left lateral transfer zone or fault the western boundary of the northern okinawa trough is characterized by the gently deepening seafloor whereas that of the southern okinawa trough is marked by steep border faults suggesting more rapid subsidence in the south this together with the well developed symmetric axial faults in the south and the greater width and the lack of well developed axial zone in the north may suggest focused rifting extension in the southern okinawa trough and diffuse rifting extension in the northern okinawa trough we postulate that the diffuse rifting extension in the northern okinawa trough is due to the tectonic perturbation caused by the convergence or subduction of the topographically high and buoyant amami plateau at the northern ryukyu arc

heat flow and thermal history of the south china sea abstract a total of 589 heat flow values are available from the south china sea the values are widely scattered ranging from 9 to 181 mw m 2 with a mean of 77 mw m 2 in the northern margin the values are less scattered and the average is about 75 mw m 2 heat flow increases gradually from the northern margin to the central basin in which two high heat flow centers appear one in the east subbasin and the other in the southwest subbasin the southern margin has an average heat flow of 80 mw m 2 similar to the northern margin the western margin where the manila trench is located has an average heat flow as low as 49 mw m 2 in order to understand the high heat flow in the basin in the context of its tectonic history we carried out thermal modeling using a 2d finite element method along a profile across the northern margin a theoretical thermal history has been inferred on the basis of a multistage pure shear extension model the result shows that before miocene the basement heat flow showed relatively low values ranging from 48 to 57 mw m 2 since late miocene the basement heat flow has increased as a result of greater extension the present day high heat flow is primarily the result of pliocene extension

episodic rifting and subsidence in the south china sea the south china sea experienced at least three stages of rifting and two intervening stages of sea floor spreading since the early cretaceous its evolution can be described by an episodic model of tectonism one of thermal cooling and subsidence pulsed by temporally and spatially confined heating events analysis of regional geologic and geophysical data suggests episodes of rifting and associated thermal activities initiated during the late cretaceous the late eocene and the late early miocene the rift system corresponding to the first episode trends northeast southwest whereas those of the second and third trend east west these two trends coincide with the orientations of the major tectonic lineations within the basin age estimates from heat flow and bathymetric data suggest the oceanic crust in the southwest subbasin is considerably older 55 ma than that in the northwest 35 36 ma or east 32 ma subbasins the episodic tectonic model is supported by basin subsidence analysis subsidence especially subsidence rate curves derived from the regional well data demonstrates that unlike a classic atlantic passive margin thermal subsidence in the south china sea was punctuated by rapid subsidence events which are chronologically consistent with the rifting episodes in terms of hydrocarbon potential the episodes of rifting and drifting would be conducive to the development of overprinted structures and the deposition of several discrete transgressive packages of source rocks and reservoirs separated by widespread unconformities the thermal maturity of sedimentary organic matter affected by episodic rifting and subsidence may be greater than expected on a purely passive margin of equivalent age that had not experienced repeated heating

geologic and hydrologic controls on the movement of water through a thick heterogeneous unsaturated zone underlying an intermittent stream in the western mojave desert southern california 1 a two dimensional axially symmetric unsaturated flow model was developed to test hypotheses about geologic and hydrologic controls on the movement of water through the thick heterogeneous unsaturated zone underlying oro grande wash in the mojave desert california heterogeneity within the unsaturated zone was simulated with multiple realizations of subsurface geology estimated on the basis of transition probability markov chain statistics model results show lateral spreading of water away from the wash was best approximated by realizations that include thin horizontally extensive clay layers that impede the downward movement of water there was a wide range in model responses for these realizations and the movement of water through unsaturated zones containing thin horizontally extensive clay layers may be more difficult to predict than water movement through unsaturated zones where clay layers are less extensive for realizations having less extensive clay layers the range of model responses decreased with time and model results became increasingly similar as water encountered larger volumes of material

cretaceous and cenozoic cooling history across the ultrahigh pressure tongbai dabie belt central china from apatite fission track thermochronology abstract the crystalline terrane of the tongbai dabie region central china comprising the earth s largest ultrahigh pressure uhp exposure was formed during triassic collision between the sino korean and yangtze cratons new apatite fission track aft data presented here from the uhp terrane extends over a significantly greater area than reported in previous studies and includes the eastern dabie the hong an northwestern dabie and tongbai regions the new data yield ages ranging from 44 3 to 142 36 ma and mean track lengths between 10 and 14 4 m thermal history models based on the aft data taken together with published 40 ar 39 ar k ar apatite and zircon u th he and u pb data exhibit a three stage cooling pattern that is similar across the study region commencing with an early cretaceous rapid cooling event followed by a period of relative thermal stability during which rocks remained at temperatures within the aft partial annealing zone 60 110 c and ending with a possible renewed phase of accelerated cooling during pliocene to recent time the first cooling phase followed large scale transtensional deformation between 140 and 110 ma and is related to early cretaceous eastward tectonic escape and pacific back arc extension between this phase and the subsequent slow cooling phase a transition period from 120 to 80 ma to 70 to 45 ma along the tan lu fault was characterised by a relatively low cooling rate 3 5 c ma this transition is likely related to a tectonic response associated with the mid cretaceous subduction of the izanagi pacific plate as well as lithospheric extension and thinning in eastern asia the present regional aft age pattern is therefore basically controlled by the early cretaceous rapid cooling event but finally shaped through active cenozoic faulting following the transition phase the subsequent slow cooling phase pattern implies a net reduction in horizontal compressional stress corresponding to increased extension rates along the continental margin due to the decrease in plate convergence modelling of the aft data suggests a possible pliocene recent cooling episode which may be supported by increased rates of sedimentation observed in adjacent basins this cooling phase may be interpreted as a response to the far field effects of the frontal india eurasia collision to the west approximate estimates suggest that the total amount of post 120 ma denudation across the uhp orogen ranged from 2 4 to 13 2 km for different tectonic blocks and ranged from 0 8 to 9 7 km during the cretaceous to between 1 7 and 3 8 km during the cenozoic

thermal history reconstruction using apatite fission track analysis and vitrinite reflectance a case study from the uk east midlands and southern north sea apatite fission track analysis afta is a method of obtaining ther mal history information in sediments in sections that have been hotter in the past afta provides estimates of maximum palaeotemperatures and the time at which a sedimentary section began cooling from maximum palaeotempera tures it is useful for studying the thermal history of sequences containing source rocks and can provide information critical to the understanding of the timing of oil generation integration of afta and vitrinite reflectance vr data allows a coherent thermal history framework to be established and a formal method of analysing palaeogeothermal gradients has been developed by combining afta and vr data this approach allows definition of the major facets of thermal history based on directly measurable parameters rather than on assumed values of palaeo heatflow and provides rigorous estimates of the amount of uplift and erosion the case study demonstrates the application of this approach to the east midlands shelf region here afta data have revealed an episode of maximum palaeotemperatures prior to cooling commencing at around 60 ma combined afta and vr data show that this cooling was due to kilometre scale early ter tiary uplift and erosion under near normal geothermal gradients our estimates of uplift and erosion are significantly greater than those of pervious workers and show that uplift and erosion was not restricted to the recognized axes of inversion but was regional in extent this has implications for the evolution of source rock maturity in this region and in other basins in around the uk where afta has indicated early tertiary heating and where the extent and amount of tertiary uplift and erosion may have also been underestimated by previous workers apatite fission track analysis afta tm is a method of obtaining thermal history information in sediments and is particularly useful for studying the thermal history of sequences containing hydrocarbon source rocks as well as providing estimates of maximum palaeotemperatures afta provides a direct estimate of the time at which a sedimentary section began cooling from its maximum palaeotemperature a key advantage over traditional geochemical methods in many situations this knowledge is critical to the understanding of the timimg of oil generation and migration in relation to trap formation information on the timing of maximum palaeotempera ture can also be of significant value in the interpretation of vitrinite reflectance vr data and combination of afta and vr data allows a consistent integrated thermal history interpretation the afta technique is applied most usefully in sedimentary sections which have been hotter in the past than they are at the present day it is therefore applicable to large regions of britain and the uk continental shelf that have been subject to deeper burial in the past or affected by other sources of heating the basis of the technique has

thermal history and tectonic subsidence of the bohai basin northern china a cenozoic rifted and local pull apart basin the bohai basin is a part of the larger bohai bay basin a cenozoic rifted intraplate basin heat flow measurements show that the bohai basin is characterized by present day heat flow varying between 53 and 74 mw m 2 with a mean of 63 mw m 2 however thermal history analyses derived from vitrinite reflectance vr and apatite fission track aft data indicate that tertiary cooling took place following a period of much higher paleo heat flow 70 90 mw m 2 prior to 25 million years to the present furthermore tectonic subsidence analysis reveals that the bohai basin experienced episodic sub rifting processes from the eocene to the end of the oligocene the post rift thermal subsidence was superimposed by intensified subsidence from the late miocene 12 million years in the bozhong depression and from the early quaternary 2 4 million years in the east liao bay indicating a rejuvenation of sedimentation related likely to transpressional structures developed locally on strike slip faults the present results indicate that there is good agreement between the reconstructed thermal history and the timing of the tectonic subsidence stages within the bohai basin the bohai basin is an early cenozoic rifted and local pull apart sub basin of the larger bohai bay basin 2001 elsevier science b v all rights reserved

thermal regime and petroleum systems in junggar basin northwest china abstract the conversion of organic matter into oil and gas depends upon temperature and time and the study of thermal maturation of oil source rocks in a petroleum system is of importance for formation of a petroleum system based on the temperature data from 196 wells and thermal conductivity measurements of 90 core samples altogether 35 heat flow data are obtained in the junggar basin the results show that the junggar basin is a relatively cold basin at present with a mean temperature gradient and heat flow of 21 c km and 42 mw m 2 respectively thermal history reconstructed from vitrinite reflectance data indicates that the paleozoic formations experienced their maximum paleotemperature during the permian and triassic at higher paleoheat flow of about 85 mw m 2 and that the basin then cooled down to the present low heat flow the high paleoheat flow can be attributed to the carboniferous to permian rifting the thermal evolution has a quite important effect on the formation and evolution of the petroleum systems in the junggar basin i e the permian and the jurassic systems the jurassic petroleum system is quite limited in space for the cooled thermal regime during the meso cenozoic and the source rocks of the middle lower jurassic entered the oil window only along the north tianshan foreland region where the jurassic is buried to the depth of 5 7 km at present in contrast the middle lower permian source rocks have experienced oil and gas generation in late permian to triassic and the permian petroleum system was formed prior to the triassic when the upper paleozoic formations reached their maximum paleotemperature due to higher paleoheat flow

neogene quaternary postrift tectonic reactivation of the bohai bay basin eastern china bohai bay basin located in eastern china is considered a cenozoic rifted basin the basin is atypical in terms of its neogene quaternary postrift subsidence history in that it experienced intensive tectonic reactivation rather than the relative tectonic quiescence experienced during this stage by most rift basins this neogene quaternary tectonic reactivation arose principally in response to two tectonic events 1 activity on a dense array of shallow faults and 2 accelerated tectonic subsidence that occurred during the postrift stage these two events were neither strictly temporally nor spatially equivalent the dense array of shallow faults form a northwest southeast trending belt in the central part of the basin with displacement induced by the reactivation of older northeast and northwest trending basement faults and an associated substantial component of strike slip displacement occurring after 5 3 ma the intensive reactivation of these faults contributed to the atypically accelerated rate of postrift tectonic subsidence of the basin that commenced ca however this was not the sole cause of this accelerated tectonic subsidence a combination of geological activity deep within the crust led to the buildup of intraplate stresses and this combined with ongoing thermal subsidence acted as an additional contributory factor that drove unusually high rates of subsidence for this basin this episode of accelerated postrift tectonic reactivation resulted in conditions favorable for hydrocarbon accumulation

new methodology for computation of the earth s polarizability from telluric borehole logging measurements taken at different frequencies an important approach for computation of the earth s polarizability is achieved by developing a novel method with new parameters called natural percent frequency effect npfe and natural metal factor nmf resulting from telluric logging data taken at different frequencies the essential advantage of the developed approach relies on using natural electrical currents instead of an artificial electrical source usually needed in the standard frequency domain applied in the induced polarization method furthermore a good qualitative correlation has been found between the new parameters and those of the traditional induced polarization method obtained in time and frequency domains the new method has been tested in well 32 in the rouez mine in france where sulphide mineralization is well known to occur

collision rotation and back arc spreading in the region of the okhotsk and japan seas the india eurasia collision caused extensive deformation in the eurasia continent since late eocene time we propose that back arc spreading in the okhotsk and japan seas was related to the movement of microplates relevant to the india eurasia collision the kuril basin of the okhotsk sea and the basins of the japan sea were formed as back arc basins simultaneously their late oligocene to middle miocene age is constrained by sediment stratigraphy basement depth and heat flow data the movements of two microplates the okhotsk and amuria plates are significant for the tectonics of the okhotsk and japan seas simultaneous retreat of both microplates from trench hinge lines caused back arc spreading in the kuril basin and the japan sea the amuria plate moved north northeastward due to the india eurasia collision this caused pull apart opening of the baikal rift along a transform boundary between the siberia and amuria plates and a collision along the stanovoy range at its northern margin this movement triggered a clockwise rotation of the okhotsk plate with a component of dextral collision between the okhotsk and amuria plates which is well observed along the central zone of the sakhalin hokkaido islands between the two back arc plates the clockwise rotation of the okhotsk plate is suggested by the southwestward fan shaped opening of the kuril basin the kuril basin narrows to the northeast and terminates south of the kamchatka peninsula where a relative rotation pole between the okhotsk and kuril forearc plates is located the kamchatka peninsula was a zone of collision on the other side of the clockwise rotating okhotsk plate during the opening of the kuril basin the sredinny range in the kamchatka peninsula is one of the results of the collision between the okhotsk plate and the forearc plate of the kuril arc the bending of the japanese islands occurred in association with the back arc spreading of the yamato basin of the japan sea

seismic stratigraphy and structural analysis of the northern east china sea shelf basin interpreted from multi channel seismic reflection data and cross section restoration analysis of multi channel seismic data from the northern east china sea shelf basin ecssb reveals three sub basins socotra domi and jeju basins separated by structural highs hupijiao rise and faulted basement blocks these sub basins show a typical rift basin development faulted basement and syn rift and post rift sedimentation separated by unconformities four regional unconformities including the top of acoustic basement have been identified and mapped from multi channel seismic data faults in the acoustic basement are generally trending ne parallel to the regional structural trend of the area the depths of the acoustic basement range from less than 1000 m in the northwestern part of the domi basin to more than 4500 m in the socotra basin and 5500 m in the jeju basin the total sediment thicknesses range from less than 500 m to about 1500 m in the northwest where the acoustic basement is shallow and reach about more than 5500 m in the south interpretation of seismic reflection data and reconstruction of three depth converted seismic profiles reveal that the northern ecssb experienced two phases of rifting followed by regional subsidence the initial rifting in the late cretaceous was driven by the nw se crustal stretching of the eurasian plate caused by the subduction of the pacific plate beneath the eurasian plate extension was the greatest during the early phase of basin formation estimated rates of extension during the initial rifting are 2 6 5 and 3 5 in the domi jeju and socotra basins respectively a regional uplift terminated the rifting in the late eocene early oligocene rifting and extension although mild resumed in the early oligocene while fluvio lacustrine deposition continued to prevail the estimated rates of extension during the second phase of rifting are 0 7 0 8 and 0 5 in the domi jeju and socotra basins respectively a second phase of uplift in the early miocene terminated the rifting marking the transition to the post rift phase of regional subsidence regional subsidence dominated the study area between the early miocene and the late miocene an inversion in the late miocene interrupted the post rift subsidence resulting in an extensive thrust fold belt in the eastern part of the area uplift and subsequent erosion were followed by regional subsidence highlights this paper presents 2d seismic mapping of the northern east china sea shelf basin structural and stratigraphic evolution of the basin have been investigated we have also reconstructed three depth converted seismic reflection profiles cross section restoration provided quantitative information about extension rates

estimation of spatial recharge distribution using environmental isotopes and hydrochemical data ii application to aravaipa valley in southern arizona u s a abstract in part i a mathematical model was developed to estimate the spatial distribution of annual recharge rates into an aquifer using environmental isotopes and hydrochemical data in part ii the model is applied to real data from the aravaipa valley in southern arizona these data suffer from a paucity of hydrologic information but contain numerous isotopic and hydrochemical analyses the model is able to extract from the available data both qualitative and quantitative information about recharge into and flow through the shallow unconfined aquifer in the valley the model shows that this aquifer is replenished primarily by lateral recharge from the pediments and the tributary stowe gulch basin as well as by upward leakage from the underlying confined aquifer recharge from the aravaipa creek is relatively minor lateral recharge from the eastern pediments into the unconfined aquifer exceeds that from the western pediments by a factor of two the western pediments are a major source of recharge for the confined aquifer these results are tentative because independent means to verify them are currently lacking we are encouraged however that the mass balance errors of water and dissolved constituents do not exceed 4 and that the flow rate obtained from darcy s law at one location within the unconfined aquifer in which transmissivity is known agrees with model prediction while chemical reactions are ignored in the model some of the isotopic and chemical species show sufficient spatial variability due to mixing to justify the approach this is supported by analyses of equilibrium water mineral interactions conducted by wateqf

cenozoic basins in northern taiwan and tectonic implications for the development of the eastern asian continental margin abstract north of taiwan four offshore tertiary basins extend seaward from the inner shelf of the east china sea to the west of the okinawa trough these basins are characterized by rifting features with ne sw trending half grabens and fault blocks episodic rifting events have taken place from paleocene to early miocene with the eastward shift of depositional centers the paleogene rift basins are filled primarily with lacustrine to shallow marine sediments but also contain a slight amount of pyroclastics and basaltic flows regional subsidence has dominated during the late tertiary and these paleogene half grabens have united into a large marginal sea basin overlain by a neogene sedimentary wedge of shallow marine sediments a fifth basin the paleogene hsuehshan half graben trough in present day northern taiwan has been deformed into mountain ranges by the collision of the luzon arc with the eastern asian margin during the late cenozoic era the tectonic development of eastern asian margin in northern taiwan region has evolved into two phases first the eastward retreat of the west pacific subduction zone and accompanied rifting of continental crust occurred during late cretaceous to eocene times second as the intensity of rifting decreased thermal subsidence of eastern asian margin prevailed and subsequently caused a tilting seaward continental margin on which a large marginal sea basin rests collision of the luzon arc with the eastern asian margin in taiwan deformed the paleogene hseuhshan trough into mountain ranges late miocene to present

extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china abstract in southeastern china the wugongshan massif consists of metamorphic rocks and granites generally considered as basement rocks formed during an early paleozoic orogeny our structural and radiometric reappraisal of this massif shows that it results from a mesozoic doming in the metamorphic rocks the foliation defines an e w elliptical shape and bears a n s stretching lineation the axial zone of the dome is occupied by oriented plutons the outer part of the dome consists of devonian quartzite carboniferous permian limestone and triassic jurassic sandstone ductile deformation observed in the permian carbonates and older units develops contrasting kinematics the northern and southern flanks present top to the north and top to the south motions respectively the same divergent pattern of motion is recorded from brittle structures up to the jurassic sandstone the late cretaceous red beds are undeformed in the axial zone coaxial flow indicated by symmetric pressure shadows and quartz fabrics predominates along the n and s flanks of the dome post folial recumbent folds are symmetrically overturned to the n and s respectively but at the two extremities of the dome the fold axes are parallel to the stretching lineation 40 ar 39 ar ages of biotite and muscovite from mylonite and granite suggest a late triassic age for the ductile deformation and an early cretaceous age for the final doming the wugongshan dome is similar to a metamorphic core complex formed in an extensional tectonic regime a model which emphasizes plutonism is discussed from permian to early cretaceous southeastern china was a subduction type orogen the crust of which was thickened by accretion of mantle derived magmas the emplacement of a large amount of mesozoic granitoids in southeastern china promoted thermal softening and gravitational instability that allowed the crust to extend the formation of the wugongshan dome and other metamorphic core complexes appears to be a the direct consequence of plutonic activity and crust rheology

source to sink transport in the oligocene huagang formation of the xihu depression east china sea shelf basin abstract the huagang formation is the most important hydrocarbon reservoir in the xihu depression of the east china sea shelf basin reconstructing the provenance and transport pathways of its main sand bodies is of great significance to oil and gas exploration previous provenance studies were mainly based on heavy mineral analyses and showed multiple source areas but so far quantitative estimates on provenance are lacking detrital zircon u pb dating combined with heavy mineral analysis is an effective tool to quantitatively investigate sediment provenance in this paper we use the la icp ms method for u pb dating of detrital zircons of 18 samples from 13 drill cores in the xihu depression to determine the sediment provenance of the oligocene huagang sandstones the u pb zircon dating results show three different age groups in which precambrian ages dominate 60 and paleozoic and mesozoic ages each account for 20 the precambrian zircons are mainly derived from the hupijiao uplift which indicates a dominant and long distance north to south transport direction the provenance of the paleozoic zircons is mainly from the diaoyu islands folded uplift belt in the east while the haijiao and yushan uplifts in the west are the main source region for the mesozoic zircons the northern provenance transport pathway is dominated by axial channels incised valleys are observed in the western source and a transfer zone dominates the eastern provenance the integration of all data results in a new schematic model of source to sink transport in the huagang sandstones demonstrating the complexity of multiple source rocks and sediment transport pathways in the oligocene xihu depression

charge history of co2 in lishui sag east china sea basin evidence from quantitative raman analysis of co2 bearing fluid inclusions abstract the accumulation of carbon dioxide in natural gas reservoirs is common and co2 gas fields have been widely discovered in the world in the last decades three co2 pools were discovered in lishui sag east china sea basin geochemical proxies indicate that co2 in these gas reservoirs is dominated by mantle source volcano degassing although three volcanic events occurred in the formation of these reservoirs the co2 charging period is not clear in this study pure co2 co2 rich and h2o rich fluid inclusions were found in healed micro fractures and overgrowth zones of quartz in the reservoir of lishui sag the composition and density of two h2o rich inclusions two co2 rich inclusions and twenty three pure co2 inclusions were determined by raman quantitative analysis the burial depth of co2 fluid inclusion assemblages fia can be determined by the trapping pressure constrained from raman quantitative analysis and thermodynamic models the combination of c he isotope analyses pt entrapment conditions of co2 bearing inclusions feature of fault activity and simulation of burial history permits to assign periods of co2 fluid activity the low density 0 15 g cm 3 co2 gas inclusions recorded an early period of co2 activity eruption to be related with the late paleocene volcanic event the mid density 0 45 g cm 3 and high density 0 75 g cm 3 co2 inclusions were assigned to the miocene volcanic event and to a later co2 charging event during pliocene

origin and time evolution of subduction polarity reversal from plate kinematics of southeast asia we present a regional model of plate geometry and kinematics of southeast asia since the late cretaceous embedded in a global plate model the model involves subduction polarity reversals and sheds new light on the origin of the subduction polarity reversal currently observed in taiwan we show that this subduction zone reversal is inherited from subduction of the proto south china sea plate and owes its current location to triple junction migration and slab rollback this analysis sheds new light on the plate tectonic context of the taiwan orogeny and questions the hypothesis that northern taiwan can be considered an older more mature equivalent of southern taiwan

stratigraphic framework and evolution of the mid late quaternary since marine isotope stage 8 deposits on the outer shelf of the east china sea abstract the east china sea ecs is a vast river dominated depositional basin because of its broad shelf and extensive river sediment supply this study investigated the mid late quaternary stratigraphic framework and evolution of the outer ecs shelf based on a borehole core dh02 and seismic profiles seven sedimentary facies were recognized in the core sediments according to lithology grain size composition sediment structure and microfossil assemblages while eight unconformity bounded major stratigraphic units were identified in the seismic profiles based on seismic core correlations dating data radiocarbon and optically stimulated luminescence and comparison between sedimentary cycles and sea level curves the 100 m thick strata below the seafloor were divided into three sequences corresponding to glacial interglacial sea level cycles of marine isotope stage mis 1 2 mis 3 6 and mis 7 8 sq1 sq3 from top to bottom in particular sq1 is developing in the present sea level highstand and consists mainly of deposits of transgressive systems tract tst including tide influenced river tidal flat and tide dominated estuarine facies sq2 and sq3 consist mainly of prodelta and related inner shelf facies of forced regressive systems tract frst and transgressive deposits similar to those of sq1 for all three sequences a thin sand sheet layer of open shelf facies represents deposits of highstand systems tract hst deposits of lowstand systems tract lst were typically represented by river facies in addition comprehensive analyses of seabed sand ridge distribution core sediment characteristics and ridge deposition mechanism suggest that the occurrence of a paleoestuary with transgression determined the development of a tidal sand ridge field based on all these results a conceptual stratigraphic sequence model in association with the deposition of lst tst hst and frst was constructed overall our stratigraphic framework along with a comparison of the sequence stratigraphy to that of other shelves suggested that glacial interglacial sea level fluctuations huge amounts of river sediment supply active subsidence gentle shelf topography and marine erosion processes transgression and regression controlled the mid late quaternary stratigraphic development of the ecs shelf

first order seismic attributes for clastic seismic facies interpretation examples from the east china sea abstract seismic attributes for the interpreting explorationist are numerous some are useful some duplicative and some less useful however with respect to optimizing a systematic basin analysis approach which relies upon heavily upon integrating seismic facies there are eight particularly useful attributes which have clear geophysical meaning strong underlying geological rock fluid implications and which for clastic depositional environments greatly assist in determining seismic facies associated paleoenvironments and lessening the number of interpretive possibilities they are amplitude envelope chaos cosine of phase dip deviation instantaneous frequency q relative acoustic impedance and variance a systematic application of these first order attributes for the east china sea in particular and for other clastic environments in general allows a first pass assessment of a basin s exploration potential through seismic reconnaissance an interpretive reconnaissance whose accuracy is limited only by the seismic fidelity of the lines and logic of the assumed geology employed

heat flow and thermal evolution of a passive continental margin from shelf to slope a case study on the pearl river mouth basin northern south china sea abstract the pearl river mouth basin prmb the largest basin in the northern continental margin of the south china sea scs has been one of the key areas to characterize geothermal field and thermal evolution of a passive continental margin the thermal history of the pearl river mouth basin is related to the seafloor spreading of the scs in the late early oligocene heat flow measurements show that the prmb is characterized by a high background heat flow with average heat flow of 71 8 13 6 mw m2 the present day heat flow of the northern scs increases from the northern shelf with the thick crust to the southern slope with the thinned crust this study employs forward and inverse modeling to simulate the rift and post rift processes exampled by four wells at different structural settings two thermal evolution models of the prmb are established for continental shelf and continental slope in the continental shelf heat flow increased rapidly twice during the syn rift stage and then followed by continuous thermal subsidence with heat flow value decreased during the post rift stage while the heat flow in the slope continuously increased due to lithospheric thinning mantle upwelling and resulting multi episode seafloor spreading in scs during the neogene post rift stage which is different from the previously proposed decreasing heat model for the slope during the post rift heat flow gradually reduced after the cessation of the sea floor spreading 10 ma the local multi staged magmatic activities mainly contribute to the high level of maturity in the liwan sag located in the lower slope

symmetry of the south china sea conjugate margins in a rifting drifting and collision context abstract the symmetry of conjugate rifted margins is a first order observable feature reflecting the geodynamic processes acting during and after continental rifting the symmetry of the south china sea scs rifted margins can be deduced from comprehensive geophysical datasets on a continental margin scale here we combine three key approaches 1 lateral fault distributions are delineated according to free air gravity anomalies 2 crustal stretching styles are mapped based on gravity inversion constrained by deep seismic profiles and 3 total extension of conjugate margins is estimated according to margin restorations and tectonic settings we infer a predominantly symmetric rifting style caused by pure shear extension with only narrow domains of asymmetric deformation in continent ocean transition cot regions that have undergone simple shear and where the lower crust of the highly thinned distal margin is embrittled before continental breakup however our analysis also suggests that this symmetry has been modified by post rift geodynamic processes southward lower crustal flow which occurred only on the southern margin due to the low viscosity of the lower crust and the slab pull induced by the subducting proto scs plate during seafloor spreading shifted the crustal stretching styles from symmetric to asymmetric the collision between the southern margin and borneo thickened the lower crust more than the upper crust at the southern end of the southern margin and shortened the southern margin this event had a large impact on the se margin but a small impact on the sw margin we conclude that 1 for the se and ne margins the crustal stretching styles shifted from asymmetric to approximately symmetric and the total extension shifted from symmetric to asymmetric 2 for the sw and nw margins the crustal stretching and total extension remained asymmetric and symmetric respectively

the sedimentary succession of the last 3 50 myr in the western south yellow sea paleoenvironmental and tectonic implications abstract the south yellow sea sys basin which is part of the west pacific continental margin began to form in the late mesozoic to early cenozoic as a result of regional tectonic activity in asia the pre middle pleistocene sedimentary history of the area remains poorly understood or controversial mainly due to a lack of long borehole cores penetrating pre quaternary strata borehole core csdp 1 300 10 m long the longest sediment core recovered thus far from the sys was drilled in 2013 in the western sys recently a reliable timescale for the core for the last 3 50 myr was obtained by magnetostratigraphy liu et al 2016a here we report the results of integrated analyses of the core including sedimentary characteristics downcore changes in environmental proxies benthic foraminifera and ostracods and accelerator mass spectrometry 14c and optically stimulated luminescence dates in addition we analyze 546 km of single channel seismic profiles and 50 km of a boomer seismic profile around the core site and correlate the regional stratigraphy the core sedimentary succession contains 17 depositional units lithofacies associations corresponding to three major seismic units reflecting a variety of depositional environments during the last 3 50 myr our results show that fluvial environments prevailed in the western sys from 3 50 to 1 66 ma followed by alternations of tidal flat to shallow subtidal environments with fluvial environments from 1 66 to 0 83 ma and alternations of modern like marine environments and fluvial environments from 0 83 ma to the present day in response to glacio eustatic sea level cycles the depositional succession during the last 3 50 myr was dominantly controlled by tectonism and glacio eustatic sea level cycles the presumed first marine transgression since the neogene in the western sys at 1 66 ma is interpreted to suggest that sea water could partially flood the zhe min uplift zmu into the sys due to tectonic subsidence and further subsidence of the zmu and the sys shelf is inferred to have resulted in establishment of normal marine environments in the sys during the highstands of glacio eustatic sea level cycles since 0 83 ma the average subsidence rates in the western sys were 120 165 m myr during the last 1 66 myr the sedimentary succession comprises fifth and fourth order sequences which are interpreted to have been driven by the 20 kyr or 41 kyr and by the 100 kyr glacio eustatic sea level cycles respectively since the late pliocene the sequences deposited since the late pleistocene are relatively complete recording deposits from mis 5 to mis 1 however the pre upper pleistocene sequences show significant stratigraphic hiatuses presumably caused by fluvial erosion during the glacial sea level lowstands and subsequent transgressive erosion this type of significant discontinuity in the sedimentary record can be considered to be diagnostic of shelf sequences controlled by glacio eustatic sea level cycles