control actions of sedimentary environments and sedimentation rates on lacustrine oil shale distribution an example of the oil shale in the upper triassic yanchang formation southeastern ordos basin nw china abstract oil shale is an important form of unconventional resources it is significant to determine the control factors on oil shale distribution abundant oil shale resources are hosted in the member chang 7 3 ch7 3 triassic yanchang formation in southeastern ordos basin nw china this study was conducted to investigate the sedimentary environment distribution and organic matter source of the ch7 3 oil shale by a combined study of outcrops core data organic and element geochemical indices the controlling factors of the oil shale distribution were determined by an analysis of sedimentary environments and geochemical features of the oil shale sedimentary facies analysis based on outcrops and core data indicated that the ch7 3 oil shale was deposited in lacustrine delta environments warm and moist climates and reducing conditions indicated by major and trace elements were favorable to organic matter production and preservation rock eval pyrolysis showed that the organic matter of the ch7 3 oil shale is from both lacustrine phytoplankton and terrigenous higher plants the organic matter from terrigenous higher plants was probably transported into the deep lake by gravity flows sedimentary facies and la yb n values show that the spatial distribution of oil shale was controlled by sedimentary environments and sedimentation rates in the deep lake area near to delta turbidite fan deposition systems terrestial organic matter input was bounteous and sedimentation rates were moderate which were beneficial to organic matter accumulation and preservation providing favorable conditions for oil shale formation in delta turbidite fan deposition systems high sedimentation rates led to organic matter dilution in the deep lake area far from delta turbidite fan deposition systems sedimentation rates were relatively low and organic matter was easily degraded in addition only lacustrine organic matter input with no terrestial organic matter input inhibited organic matter enrichment

impact of india asia collision on se asia the record in borneo abstract borneo occupies a central position in the sundaland promontory of se asia it has a complex cenozoic geological history of sedimentation and deformation which began at about the same time that india is commonly suggested to have started to collide with asia some tectonic reconstructions of east and se asia interpret a large se asian block with borneo at its centre which has been rotated clockwise and displaced southwards along major strike slip faults during the cenozoic due to the indentation of asia by india however the geological history of borneo is not consistent with the island simply forming part of a large block extruded from asia the large clockwise rotations and displacements predicted by the indentor model for borneo are incompatible with palaeomagnetic evidence and there is no evidence that the major strike slip faults of the asian mainland reach borneo seismic tomography shows there is a deep high velocity anomaly in the lower mantle beneath se asia interpreted as subducted lithosphere but it can be explained just as well by alternative tectonic models as by the indentor model very great thicknesses of cenozoic sediments are present in borneo and circum borneo basins and large amounts of sediment were transported to the crocker turbidite fan of north borneo from the eocene to the early miocene but all evidence indicates that these sediments were derived from local sources and not from distant sources in asia elevated by india asia collision the cenozoic geological history of borneo records subduction of the proto south china sea and miocene collision after this ocean lithosphere was eliminated and a variety of effects resulting from long term subduction beneath se asia there is little to indicate that india asia collision has influenced the cenozoic geological record in borneo

peculiar geometry of northern luzon philippines implications for regional tectonics of new gravity and paleomagnetic data 1 the northern termination of the philippine archipelago is remarkably abrupt the distinctive almost rectangular shape of northern luzon is a consequence of the almost simultaneous disappearance near 18 n of the central cordillera the much narrower sierra madre and the broad floodplain of the cagayan river the floodplain is underlain by a deep sedimentary basin that is closed off just inland of the coast by an ene wsw structural high known as the sicalao ridge gravity surveys show that the ridge has steep flanks that are almost certainly defined by faulting in the same region there is also a dramatic change in the luzon arc which is the volcanic expression of subduction of the south china sea the volcanic centers in the central cordillera the north luzon segment of the arc are all now inactive but further north eruptions are frequent on the small eastern islands of the bashi segment the differences between the north luzon and bashi segments suggest that they had very different geological histories until the late neogene but the evolution of northern luzon is so poorly understood that it is not even known on which plate it originated new paleomagnetic data and the existence of the sicalao ridge provide important constraints on reconstructions and when combined with geological data favor the possibility that in the paleogene the central cordillera and sierra madre were combined as parts of an arc at the southern margin of the philippine sea the sicalao ridge can be interpreted as a rift margin feature created during the detachment of luzon from continental sundaland

the marinduque intra arc basin philippines basin genesis and in situ ophiolite development in a strike slip setting the marinduque basin is a marine intra arc basin in the north central philippine volcanic arc system a suite of marine geophysical observations show the basin as a whole to be rhombic in shape with its long axis trending north northwest a conspicuous volcanic ridge trends east northeast across the basin dividing it into two smaller active depocenters symmetric linear magnetic anomalies striking parallel to and centered over the central volcanic ridge indicate that it formed by extension in a north south direction by a process analogous to sea floor spreading geometric and temporal relations between the central volcanic ridge and several en echelon sets of north trending left stepping faults indicate that sea floor spreading occurred in the extensional stepover zone of a left lateral strike slip fault system and that the marinduque basin as a whole is a composite pull apart basin whose floor is in part composed of oceanic type crust the evolution of the central volcanic ridge presents an actualistic model for in situ development and emplacement of ophiolites in an island arc setting the presently active left lateral philippine fault zone truncated the eastern flank of the basin as well as the central volcanic ridge following their initial formation shortening associated with a probable restraining bend in the philippine fault has resulted in uplift of basin flank sediments which have been thrust back toward the basin interior the philippine fault has also displaced fragments of the ridge and basin floor toward the north the overall history of the marinduque basin further suggests that strike slip processes may play an important role in the origin and growth of intra arc basins such basins may ultimately become isolated in a forearc or backarc setting

deep lacustrine sandy debrites and turbidites in the lower triassic yanchang formation southeast ordos basin central china facies distribution and reservoir quality abstract the deep lacustrine gravity flow deposits are widely developed in the lower triassic yanchang formation southeast ordos basin central china three lithofacies include massive fine grained sandstone banded sandstone and massive oil shale and mudstone the massive fine grained sandstones have sharp upper contacts mud clasts boxed shaped gamma ray gr log but no grading and bouma sequences in contrast the banded sandstones display different bedding characteristics gradational upper contacts and fine upward the massive fine grained sandstones recognized in this study are sandy debrites deposited by sandy debris flows while the banded sandstones are turbidites deposited by turbidity currents not bottom currents the sediment source for these deep gravity flow sediments is a sand rich delta system prograding at the basin margin fabric of the debrites in the sandy debris fields indicates initial formation from slope failure caused by the tectonic movement as the sandy debris flows became diluted by water and clay they became turbidity currents the deep lacustrine depositional model is different from the traditional marine fan or turbidite fan models there are no channels or wide lobate sand bodies in the lower triassic yanchang formation layers within the sandy debrites have higher porosity 8 14 and permeability 0 1 4 md than the turbidites with lower porosity 3 8 and permeability 0 04 1 md consequently only the sandy debrites constitute potential petroleum reservoir intervals results of this study may serve as a model for hydrocarbon exploration and production for deep lacustrine reservoirs from gravity flow systems in similar lacustrine depositional environments

controls on organic matter accumulation in the triassic chang 7 lacustrine shale of the ordos basin central china abstract the triassic chang 7 formation is a rich lacustrine source rock in the ordos basin central china petrographic and geochemical analyses were performed in order to research the mechanism of organic matter om enrichment in the chang 7 shales bulk geochemical data indicate that the om rich shales were formed in a fresh and brackish water which is not usually the case for high toc total organic carbon content sediments therefore there must be some special conditions favorable for om enrichment in chang 7 shales petrography and element geochemistry show that the chang 7 om rich shales are abundant in om enriched laminae framboidal pyrites collophanes and some elements including iron fe diphosphorus pentoxide p2o5 copper cu vanadium v molybdenum mo and uranium u high bio productivity algae blooming and anoxic depositional environments are critical for om enrichment as the organic carbon contents increase the fe p2o5 cu v mo and u element contents increase as well and the ratios of u th and v v ni are growing many geochemical data demonstrate that the water was oxic while the environment under the sediment water interface was anoxic as a result of a high organic supply that sufficiently consumed oxygen taking into account the geological settings and our previous studies we propose that the frequent volcanic events and hydrothermal activity caused by the collision of the north china landmass with the yangtze landmass and consequential formation of the qingling mountains had a significant role in the om enrichment in the fresh and brackish lacustrine shales deposition of volcanic ash into aqueous environments might lead to the increase of some key nutrients such as fe and p2o5 which might enhance primary bio productivity new evidence for hydrothermal activity the reddingite was demonstrated in this study not only can the hydrothermal activity provide elements necessary for life but is also favorable for formation of anoxic settings the deposition of the chang 7 lacustrine om rich shales can be explained using the high bio productivity driven model which is related to volcanic events and hydrothermal activity as a consequence of regional tectonic movements an anoxic depositional setting is beneficial for om preservation and slow sedimentation rates in the deep lacustrine environments are favorable for om enrichment

aspects of the tectonic evolution of china the subject of this special publication is one of the most interesting in global geoscience the tectonic evolution of china the assemblage of terranes that underlie this part of the world provides outstanding opportunities to elucidate global processes and many of the factors that shape the earth s lithosphere are best exemplified by the geology of china and its immediately adjacent areas in addition there are geological features that are particular and unique to the region some have been the focus of recent attention and have attracted international interest because of their global importance this volume provides accounts of up to date research by chinese and international geological teams on key aspects of the tectonic evolution of china and its surrounding areas the papers describe the formation of the geological terranes that make up this part of east asia place constraints on plate tectonic models for their assembly and provide accounts of unique geological feature of the subcontinent

formation distribution and resource potential of the sweet areas sections of continental shale oil in china abstract shale oil refers to oil stored in organic rich shale it is an important part of unconventional oil and provides a large amount of resources based on the systematic study of the geological characteristics of shale oil in china s major continental basins the geological connotation of the sweet area section in shale oil is proposed in this paper and it refers to areas sections that can be preferentially explored and developed in oil bearing shale formations under current economic and technical conditions the formation conditions and distribution characteristics of continental shale oil in china are analyzed with a focus on the geological properties of the triassic yanchang formation in the ordos basin the cretaceous qingshankou formation in the songliao basin and the permian lucaogou formation of the jimusar sag in the junggar basin it is found that the sweet areas of shale oil with medium high maturation are mainly located in thick shales with a ro greater than 0 9 and the sweet sections are mainly located in the middle and lower parts of the shale formation the geological resources of continental shale oil in the major continental basins in china are estimated to be approximately 3700 108 tons the in situ conversion process icp may be a key technology for the effective development of medium to low mature shale oil the scale maximum burial depth and present depth of the organic rich shale are proposed as the three key parameters for the optimization of pilot sites by taking the triassic yanchang formation in the ordos basin as an example using icp it is expected that the recoverable resources of china s continental shale oil will be approximately 400 500 108 tons the terminology of man made reservoir is proposed in this paper in an man made reservoir the overall industrial output of the sweet areas sections is formed by artificial intervention and the construction of an underground fracture network system with man made permeability continental shale oil may be another revolutionary source of unconventional oil and is expected to be first successfully produced in china

seismic reflection evidence for a dangerous grounds miniplate no extrusion origin for the south china sea the collision of india and asia has caused large strike slip faults to form in east asia resulting in the extrusion of crustal blocks toward the southeast since the eocene as a result of the indentation of rigid india into asia it has been suggested that the south china sea opened as a result of relative motion between a rigid indochina sundaland block and china alternative models propose that rifting and seafloor spreading were driven by trench forces to the south we test these competing models by analysis of seismic reflection profiles across the boundary between sundaland and the southern rifted margin known as the dangerous grounds we show that the southern boundary of the dangerous grounds is a subduction zone that jammed in the middle miocene to the west the dangerous grounds are bounded by a strike slip zone also active until similar to 16 ma that becomes diffuse south of the now inactive south china sea seafloor spreading center we place the western edge of the dangerous grounds just to the east of the natuna arch lupar line the west baram line is confirmed as originating as a major strike slip fault within the dangerous grounds and is continuous with the red river fault zone because the dangerous grounds were independent of sundaland until similar to 6 ma its motion cannot have been constrained by motion of this block making extrusion impossible as a mechanism to rift the south china sea se motion by both the dangerous grounds and sundaland suggests subduction forces were the primary trigger for plate motions our reconstruction places a similar to 280 km upper limit on the motion on the red river fault and a similar to 1400 km width to the paleo south china sea

travel time of accreted igneous assemblages in western pacific orogenic belts and their associated sedimentary rocks abstract accreted igneous assemblages in orogenic belts maybe divided into three types depending on whether they derive from seamounts ocean ridges or subduction related ophiolites seamount type basalts are associated with shallow water sediments mostly reefoidal limestones ocean ridge type basalts are generally overlain by pelagic cherts subduction related ophiolitic eruptives often underlain by gabbroic and ultramafic rocks are associated with hemipelagic mudstones the age of such diverse eruptive lithologic assemblages reflects the time taken for them to have traveled from their locus of generation to their place of accretion at a continental margin this relationship has been established for each type of accretionary complex examples being taken mostly from japan and the western pacific rim in order to represent evolutionary processes at a typical active plate margin in general the seamount types are older ridge types are of intermediate age and the ophiolitic types are by far the youngest usually close to zero age seamount type basalts are accreted by shallower scraping of the seamount s sediment apron together with fragments of seamount basalt ridge type by peeling due to permeability contrast and the ophiolitic types by deeper scraping as a consequence of an inflected temperature gradient accordingly it is concluded that the ophiolitic rocks are generated close to the trench and may be accreted as a result of ridge subduction

tertiary stratigraphy and basin evolution southern sabah malaysian borneo abstract new mapping and dating of strata in the southern part of the central sabah basin in northern borneo has made it possible to revise the lithostratigraphy and chronostratigraphy of the area the recognition in the field of an early miocene regional unconformity which may be equivalent to the deep regional unconformity recognised offshore has allowed the development of a stratigraphic framework of groups and formations which correspond to stages in the sedimentary basin development of the area below the early miocene unconformity lies ophiolitic basement which is overlain by an accretionary complex of eocene age and a late paleogene deep water succession which formed in a fore arc basin the late paleogene deposits underwent syn depositional deformation including the development of extensive melanges all of which can be demonstrated to lie below the unconformity in this area some localised limestone deposition occurred during a period of uplift and erosion in the early miocene following which there was an influx of clastic sediments deposited in delta and pro deltaic environments in the middle miocene these deltaic to shallow marine deposits are now recognised as forming two coarsening upward successions mapped as the tanjong and kapilit formations the total thickness of these two formations in the central sabah basin amounts to 6000 m only half of the previous estimates although the total stratigraphic thickness of cenozoic clastic strata in sabah may be more than 20 000 m

collisional orogenesis in the northern canadian cordillera implications for cordilleran crustal structure ophiolite emplacement continental growth and the terrane hypothesis during upper triassic to lower jurassic time arc magmatic rocks of the stikine terrane arc marginal sediments of the whitehorse trough igneous and mantle rocks of the cache creek ophiolite and kutcho assemblage and oceanic sedimentary and volcanic rocks of the cache creek terrane represented a magmatic arc forearc basin forearc basement and subduction complex respectively the cache creek subduction complex was thrust to the southwest over the whitehorse trough forearc basin and the stikine terrane in the middle jurassic during collision with an inboard continental domain interpretation of the various lithotectonic assemblages of the northern intermontane belt in terms of a new plate tectonic model has a number of important implications for the canadian cordillera a the model allows comparisons to be drawn with available seismic reflection interpretations of cordilleran crustal structure b ophiolite emplacement was achieved by ramping of forearc oceanic lithosphere onto thick crustal parts of a subducting plate during collisional orogenesis c island arc collision and accretion were the principal mechanisms for continental growth with relatively minor contributions from sliced off oceanic seamounts and or plateaux and d some terrane bounding faults such as the nahlin fault do not represent major lithospheric scale boundaries and their importance in tectonic reconstructions has been overemphasised

continuous hydrocarbon accumulation over a large area as a distinguishing characteristic of unconventional petroleum the ordos basin north central china abstract global petroleum exploration is currently undergoing a strategic shift from conventional to unconventional hydrocarbon resources unconventional hydrocarbons in tight reservoirs show characteristics distinct from those of conventional hydrocarbon sources hosted in structural and stratigraphic traps the characteristic features include the following a hydrocarbon source and reservoir coexist porosity and permeability are ultra low nano pore throats are widely distributed hydrocarbon bearing reservoir bodies are continuously distributed there is no obvious trap boundary buoyancy and hydrodynamics have only a minor effect and darcy s law does not apply phase separation is poor there is no uniform oil gas water interface or pressure system and oil or gas saturation varies examples of unconventional hydrocarbon accumulations are the mesozoic tight sandstone oil province and the upper paleozoic tight sandstone gas province in the ordos basin north central china generally continuous hydrocarbon accumulation over a large area is a distinguishing characteristic of unconventional hydrocarbon sources because of the great potential of unconventional petroleum resources it is believed that research on such resources will be at the forefront of the future development of petroleum geology

sedimentary and diagenetic controls on reservoir quality of low porosity and low permeability sandstone reservoirs in chang101 upper triassic yanchang formation in the shanbei area ordos basin china abstract there are many reservoirs with low porosity and low permeability in the world and many large oilfields have been found in these reservoirs unlike conventional reservoirs the genesis of low porosity and low permeability reservoirs and the controls of relatively high porosity and high permeability zones are still unclear this study takes the chang101 reservoir sandstones of the shanbei area in the ordos basin china a typical low porosity and low permeability as an example chang101 sandstones are fine grained to medium grained moderately to well sorted arkose and lithic arkose deposited in a delta plain environment it is a typical low porosity and low permeability reservoir with an average porosity of 10 21 and an average permeability of 2 88 md pore types mainly include primary intergranular pores and secondary dissolved pores the main controls on the reservoirs are the sedimentary environment and diagenesis the sedimentary environment determines the initial properties of the reservoir sandstones including the material composition and texture that determine the primary porosity and permeability diagenesis further transforms the reservoir quality to develop heterogeneity in the porosity and permeability the reservoir sandstones have undergone complex diagenetic processes and are currently in stage a of mesodiagenesis compaction accounts for the major reduction of the primary porosity of the sandstones different types of cementation have both positive and negative influences on reservoir quality carbonate cementation quartz overgrowths and some authigenic clay cementation i e i s and illite are major pore filling components that reduce the reservoir quality an appropriate amount of chlorite resists compaction and prevents quartz overgrowth but excessive chlorite coatings fill the pores and block the pore throats the laumontite cement is not only resistant to compaction but also easily dissolved to form a large number of effective secondary pores the dissolution of feldspar and rock fragments plays a role in contributing to connecting the isolated intergranular pores and increasing the secondary pores relatively high porosity and high permeability zones are deposited in high energy environment mainly delta plain distributary channel sandstones with more detrital quartz fewer rock fragments and coarser grains than other sandstones were deposited in high energy environment there is weaker compaction and less or no carbonate cement with the preservation of the primary pores by chlorite coatings and an increase in the pores by the dissolution of laumontite cement

cenozoic plate interaction of the australia and philippine sea plates hit and run tectonics abstract recent studies in northwest new guinea have shown the presence of at least two marginal basins of different age both of which formed in back arc settings the older basin opened between the middle jurassic and early cretaceous a remnant of which is now preserved as the new guinea ophiolite its obduction started at 40 ma and it was finally emplaced on the australian margin at 30 ma the younger basin was active during the oligocene to middle miocene and was obducted in the early pliocene studies of the western edge of the philippine sea also reveal an important deformation of the philippine arc in the oligocene which hitherto has remained unexplained using information from these systems paleomagnetic results kinematic reconstructions and geochemistry of the supra subduction ophiolite we present a plate model to explain the region s eo oligocene development we suggest that an extensive portion of oceanic crust extended the australian plate a considerable distance north of the australian craton as australia began its steady 7 8 cm year northward drift in the early eocene this lithosphere was subducted thus the portion of the philippine sea plate carrying the taiwan philippine arc to its present site may have actually been in contact with the ophiolite now in new guinea and obduction led to deformation of the philippine sea plate itself neogene plate kinematics transported the deformed belt in contact with the sunda block in the late miocene and pliocene this interpretation has implications for the origin for the philippine sea plate and the potential incorporation of continental fragments against its boundaries

detrital zircon provenance of the late triassic songpan ganzi complex sedimentary record of collision of the north and south china blocks the majority of the songpan ganzi triassic flysch sequence is believed to have derived from denudation of the dabie and sulu ultrahigh pressure uhp metamorphic belt in eastern china e g nie et al 1994 1 zhou and graham 1996 2 however intense debate still exists on the sources of

petroleum migration pathways and charge concentration a three dimensional model petroleum migration pathways through a basin are determined by the three dimensional distribution of discontinuous sealing surfaces which are usually parallel to bedding the petroleum migrates below the sealing surface taking the structurally most advantageous route the three dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper application of the model to the paris and williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models pathways form a dense network overlying generating areas in the central parts of basins toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing surface morphologies eventually these pathways may reach the surface as seepages it is important to integrate surface outcrops of migration routes surface seepages into migration modeling deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal fault juxtaposition or cross formational seals such as salt intrusions deflection of pathways also occurs where there are hydrodynamic conditions in response to topography driven groundwater flow zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies or juxtaposition to nonsealing strata by faults vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool it assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion

plate kinematics origin and tectonic emplacement of supra subduction ophiolites in se asia abstract a unique feature of the circum pacific orogenic belts is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust in se asia a majority of the ophiolites appear to have originated at convergent margins and specifically in backarc or island arc settings which evolved either along the edge of the sunda eurasia and australian cratons or within the philippine sea plate these ophiolites were later accreted to continental margins during the tertiary because of fast relative plate velocities tectonic regimes at the active margins of these three plates also changed rapidly strain partitioning associated with oblique convergence caused arc trench systems to move further away from the locus of their accretion we distinguish relatively autochthonous ophiolites resulting from the shortening of marginal basins such as the present day south china sea or the coral sea and highly displaced ophiolites developed in oblique convergent margins where they were dismantled transported and locally severely sheared during final docking in peri cratonic mobile belts i e the philippine mobile belt we find a series of oceanic basins which have been slightly deformed and uplifted varying lithologies and geochemical compositions of tectonic units in these basins as well as their age discrepancies suggest important displacements along major wrench faults we have used plate tectonic reconstructions to restore the former backarc basins and island arcs characterized by known petro geochemical data to their original location and their former tectonic settings some of the ophiolites occurring in front of the sunda plate represent supra subduction zone basins formed along the australian craton margin during the mesozoic the philippine sea basin the huatung basin south of taiwan and composite ophiolitic basements of the philippines and halmahera may represent remnants of such marginal basins the portion of the philippine sea plate carrying the taiwan philippine arc and its composite ophiolitic continental crustal basement might have actually originated in a different setting closer to that of the papua new guinea ophiolite and then have been displaced rapidly as a result of shearing associated with fast oblique convergence

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

paleomagnetic results from luzon and the central philippines samples were collected from 86 paleomagnetic sites from the islands of luzon marinduque mindoro panay negros cebu and mindanao in the philippine arc the sampling sites range in age from pleistocene to jurassic characteristic directions of magnetization of the samples were determined by the use of vector plots curie temperature determinations thin section studies and hysteresis studies showed that remanence of these samples is carried by fine grained pseudo single domain magnetite positive fold tests from miocene data from panay jurassic data from mindoro and cretaceous data from cebu suggest that the magnetization of these regions was acquired prior to folding rotations reported below are measured with respect to the axial goecentric dipole field the plio pleistocene data set shows no resolvable rotation for the 22 sites this data set suggests that the various terranes that make up the philippine arc have behaved as a single unit during the past 5 m y or that deformation has been below the limits of resolution the inclination data from the plio pleistocene sites have anomalously shallow inclination and are consistent with other plio pleistocene data from vietnam taiwan and the marianas these data support earlier suggestions for a late neogene offset dipole effect the late miocene sites fall into two separate groups ten sites from western luzon show evidence for around 20 of clockwise rotation in contrast to this late miocene samples from the bicol region negros marinduque and mindanao are not rotated the cause of the postlate miocene clockwise rotation of luzon is unknown but a pliocene collision of the north luzon arc with taiwan is suggested early neogene results also separate into two different populations the population from marinduque shows evidence for a large counterclockwise rotation the second early neogene population comes from panay cebu and mindanao and clearly shows evidence for a clockwise rotation the validity of this rotation is further supported by a fold test and a reversal test these early neogene data sets are consistent with a middle to late miocene collision of the palawan continental terrane and the central philippine arc data from six dikes of possible oligocene age from the zambales ophiolite are highly discordant from the present field being rotated approximately 60 clockwise the directions from these dikes are similar to a direction reported earlier from late oligocene sediments also from the zambales region these two data sets support the interpretation that the eocene direction from zambales is recording a large clockwise rotation of the region data from the mesozoic sites are from two regions data from the cretaceous pandan formation of cebu are discordant with data from the upper jurassic from mindoro the presence of a fold test from each region and a reversal test from mindoro supports the interpretation that each of these data sets is reliable the vgp of mindoro is displaced southward from the late jurassic vgp of south china suggesting a post jurassic southward migration of mindoro

plate convergence measured by gps across the sundaland philippine sea plate deformed boundary the philippines and eastern indonesia summary the western boundary of the philippine sea ph plate in the philippines and eastern indonesia corresponds to a wide deformation zone that includes the stretched continental margin of sundaland the philippine mobile belt pmb extending from luzon to the molucca sea and a mosaic of continental blocks around the ph australia sunda triple junction the gps geodyssea data are used to decipher the present kinematics of this complex area in the philippines the overall scheme is quite simple two opposing rotations on either side of the left lateral philippine fault clockwise to the southwest and counterclockwise to the northeast transfer 55 per cent of the ph sundaland convergence from the manila trench to the northwest to the philippine trench to the southeast further south 80 per cent of the ph sunda convergence is absorbed in the double subduction system of the molucca sea and less than 20 per cent along both continental margins of northern borneo finally within the triple junction area between the sundaland ph and australia plates from sulawesi to irian jaya preferential subduction of the celebes sea induces clockwise rotation of the sulu block which is escaping toward the diminishing celebes sea oceanic space from the eastwardadvancing ph plate to the south we identify an undeformed banda block that rotates counterclockwise with respect to australia and clockwise with respect to sundaland the kinematics of this block can be defined and enable us to compute the rates of southward subduction of the banda block within the flores trench and of eastward convergence of the makassar straits with the banda block the analysis made in this paper confirms that this deformation is compatible with the eastward motion of sundaland with respect to eurasia determined by the geodyssea programme but is not compatible with the assumption that sundaland belongs to eurasia as was often assumed prior to this study

fracture responses of conventional logs in tight oil sandstones a case study of the upper triassic yanchang formation in southwest ordos basin china fractures are the main fluid flow pathways in tight oil sandstones and they have a significant influence on tight oil distribution exploration and development cores and image logs are commonly unavailable because of their high costs so employing conventional logs for fracture detection is imperative for tight oil sandstones we compared the fracture response characteristics of conventional logs based on two data sets one from 8 cored wells with fracture intensities greater than 1 m 1 3 3 ft 1 and the other from 11 cored wells with fracture intensities less than 0 5 m 1 1 6 ft 1 with a case study of the upper triassic yanchang formation in southwest ordos basin china the results indicate that when tight oil sandstones are more intensely fractured the caliper log acoustic log compensated neutron log density log dual induction logs and laterolog 8 present fracture responses to some extent however it is difficult to make a distinction between fractured and nonfractured zones using conventional logs in sandstones with smaller fracture intensities the fracture response intensities of conventional logs are weak and they are influenced by fracture abundance fracture occurrence fracture scale and mineral filling degree moreover lithology fluids and rock physical properties can cause fracturelike responses hence some ambiguity exists when using conventional logs to directly identify fractures accompanying fracture sensitive conventional logs with some methods to enhance fracture response intensity and eliminate nonfracture influence could enable fracture identification in tight oil sandstones

onland signatures of the palawan microcontinental block and philippine mobile belt collision and crustal growth process a review abstract the collision of the palawan microcontinental block with the philippine mobile belt had significantly influenced the geological evolution of the philippines multiple collisions involving several fragments through space and time resulted into the collage of terranes of varying origin exposed in this part of central philippines cusping of the overriding plate volcanic arc gap ophiolite emplacement incipient back arc rifting island rotation and tilting raised coastal terraces metamorphism intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision a late early miocene to early middle miocene age 20 16 ma is proposed for the major collision between the palawan indenter and the philippine mobile belt the collision boundary is located from the northern part of mindoro through the central mountain range swinging east of sibuyan island in the romblon island group and finally threading along the buruanga peninsula and eastern side of the antique ophiolite complex before exiting and connecting with the negros trench the collision through accretion and crustal thickening has contributed to the crustal growth of the philippine archipelago

the three dimensional attenuation structures beneath the philippine archipelago based on seismic intensity data inversion abstract attenuation structures were determined for the philippine archipelago by inversion of earthquake intensity data set from 1957 to 1992 the intensity data based on the adapted rossi forel intensity scale were translated into acceleration values using a modified acceleration intensity equation a damped least squares method was used in our inversion we correlated the inversion results with other data such as observed anomalous intensity distribution present seismicity and the location of trenches and volcanic centers our results strongly indicate the association of low attenuation values with subducted slabs along the known location of trenches in the philippines for example the configuration of the philippine trench is suggested by the concentration of low attenuation values along the east side of central and southern philippines while on the western side of luzon island a low attenuation structure is consistent with the location of the manila trench the extent and depth of low attenuation values are also apparent along the eastern side of luzon in southern luzon through negros island in the central philippines the site where anomalous intensity distribution was observed coincided with the location of a noticeable low attenuation structure determined in this study moreover possible locations of an upwelling magmatic body along the numerous areas in the philippines are also indicated by the concentration of high attenuation values furthermore a possible aseismic slab which probably represents a structure that connects the manila trench with the negros trench was also inferred in eastern mindoro however it is also possible that these low attenuating values are due to the presence of continental material in this area on the basis of these initial results we suggest some modifications of the configuration of tectonic structures in several portions of the archipelago

ocean plate stratigraphy in east and southeast asia abstract ancient accretionary wedges have been recognised by the presence of glaucophane schist radiolarian chert and melange recent techniques for the reconstruction of disrupted fragments of such wedges by means of radiolarian biostratigraphy provide a more comprehensive history of ocean plate subduction and successive accretion of ocean floor materials from the oceanic plate through offscraping and underplating reconstructed ocean floor sequences found in ancient accretionary complexes in japan comprise from oldest to youngest pillow basalt limestone radiolarian chert siliceous shale and shale and sandstone similar lithologies also occur in the melange complexes of the philippines indonesia thailand and other regions this succession is called ocean plate stratigraphy ops and it represents the following sequence of processes birth of the oceanic plate at the oceanic ridge formation of volcanic islands near the ridge covered by calcareous reefs sedimentation of calcilutite on the flanks of the volcanic islands where radiolarian chert is also deposited deposition of radiolarian skeletons on the oceanic plate in a pelagic setting and sedimentary mixing of radiolarian remains and detrital grains to form siliceous shale in a hemipelagic setting and sedimentation of coarse grained sandstone and shale at or near the trench of the convergent margin radiolarian biostratigraphy of detrital sedimentary rocks provides information on the time and duration of ocean plate subduction the ages of detrital sediments becomes younger oceanward as younger packages of ops are scraped off the downgoing plate ops reconstructed from ancient accretionary complexes give us the age of subduction and accretion direction of subduction and ancient tectonic environments and is an important key to understanding the paleoenvironment and history of the paleo oceans now represented only in suture zones and orogenic belts

controls on hydrocarbon accumulation by facies and fluid potential in large scale lacustrine petroliferous basins in compressional settings a case study of the mesozoic ordos basin china abstract large scale lacustrine basins in compressional settings are an important type of petroliferous basin and the study of the characteristics of hydrocarbon accumulation in such basins is of great significance this synthesis paper takes the mesozoic ordos basin central china as a case study to establish lateral and vertical hydrocarbon accumulation patterns in this basin type and highlights how facies and fluid potential control hydrocarbon accumulation in such basins based on systematic analyses of the mesozoic source rocks sedimentary facies migration and accumulation patterns and characteristics of the oil reservoirs the hydrocarbon accumulation characteristics in the mesozoic ordos basin are discussed the analysis indicates that sedimentary facies controlled the characteristics and distribution of hydrocarbon source rocks and reservoirs while diagenetic facies controlled the quality and distribution of the reservoirs excess pressure and fluid potential controlled hydrocarbon migration directions and paths whereas facies and potential controlled the locations of oil accumulations and traps it is concluded that source rocks controlled oil bearing regions sedimentary facies controlled oil bearing plays and fluid potential controlled the locations of accumulations for shallow intervals because fluid migration is mainly controlled by buoyancy paleotopographic highs played an important role in controlling hydrocarbon accumulations for deep layers chang 7 to chang 10 members since buoyancy is less than the capillary pressure excess pressure caused by the undercompaction of mudstone and hydrocarbon generation at depth provides the driving force for lateral and vertical migration of oil and becomes the main migration force the reservoir accumulation characteristics differ laterally between regions of the basin at the periphery of the basin reservoir units are stacked in a step wise manner whereas at the center of the basin multiple reservoir intervals are vertically stacked in the form of multistorey accumulations vertically layers with different burial depths have different accumulation characteristics the paleotopography controlled hydrocarbon accumulation in shallow intervals instead excess pressure fluid potential and paleotopography controlled accumulation in deep intervals this understanding could be used to inform prospecting in other large scale lacustrine petroliferous basins in compressional settings such as the eocene green river basin in the u s a and the middle triassic gunnedah basin in australia

north luzon and the philippine sea plate motion model insights following paleomagnetic structural and age dating investigations results of one of the most comprehensive paleomagnetic and supporting geological programs ever carried out in offshore se asia on north luzon northern philippines are reported six new results based on 66 sites are reported from a total collection of 243 individual sites declinations in the data subset are sometimes scattered likely reflecting combinations of major plate and local rotations in both clockwise and counterclockwise directions and thus have a somewhat limited value for tectonic modeling the inclination data are however much more valuable and can be best explained if north luzon traveled as part of the philippine sea plate for most of its history a scenario which is compatible with the known geology of the eastern philippines and broader region in the proposed model for all of its eocene pliocene history north luzon is placed on the western edge of the philippine sea plate effectively always just to the west of the site where the benham plateau formed 40 ma the paleomagnetic data indicate a substantial northward migration of the area since the start of the neogene with an earlier interval stretching back to at least the mid early cretaceous when this part of the plate occupied equatorial latitudes post 15 ma motion of the plate has involved the indentation of the palawan microcontinental block into the western side of the philippine archipelago deformations induced by this process offer the most likely explanation for the scattered declinations observed in north luzon and areas a short distance to the south

the cretaceous southeast bohol ophiolite complex central philippines a highly disaggregated supra subduction zone ophiolite abstract the southeast bohol ophiolite complex seboc represents a complete ophiolite sequence with a pelagic chert cap yielding an early cretaceous age the residual peridotite suite of this ophiolite complex is dominated by harzburgite with rare occurrences of lherzolite and dunite pods layered ultramafic cumulate rocks made up of clinopyroxenite wehrlite dunite and massive to layered mafic cumulate rocks consisting of gabbro and norite are present although disaggregated the ophiolite complex includes a sheeted dike complex and a preponderance of sheet flows over pillow lavas in the volcanic section geologic observations such as gabbro pods included within residual harzburgite and deep water sedimentary and volcanic rocks directly overlying the harzburgite have often been reported from the mid atlantic ridge and other slow spreading centers however such situations are never encountered in the seboc geochemical data on seboc show that this ophiolite complex exhibits transitional mid ocean ridge basalt island arc tholeiite geochemical affinities this suggests formation in a subduction related marginal basin the field geological characteristics of seboc show that aside from being a harzburgite ophiolite type this crust mantle sequence was formed in a fast spreading center later tectonic events resulted in its emplacement as a forearc ophiolite

role of strike slip faulting in the evolution of allochthonous terranes in the philippines concepts of allochthonous terrane transport and emplacement are dominated by the assumption that most terranes originate on the subducting plate collide with the upper plate and are emplaced there movement of terranes along the convergent margin is recognized but is generally attributed to postcollision slip in the northern philippines allochthonous terranes originate primarily within the arc system have been translated along it by strike slip faults and were emplaced by cessation of that slip the authors suggest that in the philippines some originally vertical strike slip boundaries may have evolved into shallow dipping sutures marked by fold and thrust systems this mode of terrane evolution may be more common than generally appreciated particularly in orogenic belts developed in response to oblique convergence

triassic diorites and granitoids in the foping area constraints on the conversion from subduction to collision in the qinling orogen china abstract the western qinling is characterized by triassic granitic plutons which are keys to constrain the timing of subduction and collisional processes between the north china and south china blocks this paper presents a set of new la icpms u pb zircon geochronology major and trace element geochemistry for several representative diorite and granitoid plutons in the foping area the diorites are characterized by high mgo al2o3 y and yb contents but low sio2 sr y and la yb ratios as well as depletion of nb ta p and ti suggesting derived from a subduction related setting la icpms zircon u pb age of 216 9 1 5 ma mswd 0 69 from the diorite constrains the time of the subduction event the medium and fine grained monzogranites as well as the biotite granites exhibit relative high sio2 mgo and rb low y and yb contents and low sr y and la yb ratios as well as various depletions of nb ta p and ti these features indicate a derivation from lower continental crust but had been influenced by slab released fluids in a syn collisional setting the medium grained monzogranite and biotite granite yield la icpms zircon u pb ages of 207 3 2 1 ma mswd 1 8 and 201 6 1 2 ma mswd 1 04 respectively proposing the syn collision during ca 207 201 ma geochemical and geological evidences suggest that the granodiorites intruding in the syn collisional monzogranites were related to the post orogenic collapse after the collision between the north china and south china blocks the la icpms u pb zircon age of 189 3 2 9 ma mswd 5 6 for the granodiorite constrains the time of the post orogenic collapse our geochronological and geochemical data provide important constraints on the triassic evolution from subduction to collision then up to post collisional collapse along the qinling orogen

diagenesis of tight sandstone reservoirs in the upper triassic yanchang formation southwestern ordos basin china abstract in order to better predict the petrophysical properties of the tight sandstone reservoirs in the upper triassic yanchang formation ordos basin china the nature of the diagenetic system involved was investigated using a suite of petrographic and geochemical techniques including thin section and x ray diffraction analysis scanning electron microscopy maps mineralogy cathodeluminescence electron probe microanalysis and fluid inclusion analysis on a set of selected tight sandstone samples the sandstones investigated are texturally mature but compositionally immature with an average framework grain composition of q32f41l27 authigenic quartz calcite and chlorite coatings are the major cements while feldspars are partially dissolved two groups of quartz cement are present in the tight sandstone reservoirs smectite to illite conversion provided silica source for the first group of quartz overgrowth qo i while the silica source for the second quartz overgrowth qo ii was mainly originated from feldspar dissolution calcite cements consist of two types namely ca i and ca ii the ca i calcite cement contains no chlorite coatings and have higher concentrations of fe2 and mg2 whereas the ca ii calcite cement developed over the chlorite coatings plagioclase dissolution appears to be always accompanied by calcite cementation while k feldspar albitization forms euhedral albite locally the burial diagenesis processes were in most cases not episodic but occurred as slow adjustments in response to increased burial depths and temperatures in all the studied diagenetic minerals elemental distributions appear to be strictly constrained by the interaction of authigenic minerals involved indicating that the chemical reactions during the diagenesis comply well with the general principle of mass balance the diagenesis in the upper triassic yanchang formation tight sandstones was thus mainly developed in a closed geochemical system where mineral dissolution and precipitation are approximately balanced and diagenetic fluids were not affected by external sources significantly mechanical compaction has played a more important role in destroying the primary porosities of the upper triassic yanchang formation than the cementation

geologic and paleomagnetic evidence for a possible miocene collision in western panay central philippines the palawan metamorphic terrane represented by paleozoic basement on the northwestern tip of panay central philippines collided with the remainder of the island between late oligocene and middle miocene time subduction continued north and south of the collision zone along the manila and negros trenches respectively evidence for the collision is 1 the juxtaposition along a major fault of old melange terrane against highly metamorphosed paleozoic continental sediments similar to those exposed on palawan island itself and 2 miocene thrusting in the melange terrane oriented parallel to the suture paleomagnetic studies show that since the early miocene the island of panay has rotated 20 clockwise declination 20 9 inclination 22 1 for six sites whereas the northern philippines has rotated counterclockwise these contrasting rotations are consistent with a collision of the philippine arc with a northeastward converging palawan block

migration features of crude oil in fluvial deposits of maling oilfield in ordos basin china abstract oils in the maling oil field ordos basin are produced from fluvial deposits within the yan 9 and yan 10 subsections of the yanan formation through the analysis of pyrrolic nitrogen compounds and fluid inclusions the oil charging site migration direction and pathway and timing were interpreted in relationship with the sedimentary features and the high pressure observed in the mesozoic sequence the spatial distribution pattern of the fractionation of neutral nitrogen compounds in the crude oils suggested two possible charging positions in the studied area the ratios of the isomeric nitrogen compounds increase toward the center of the study area from both northwest and southeast directions of the region indicating that the lateral charging directions were likely from both the southeast and the northwest toward the center of the oil field the isomeric ratios of pyrrolic nitrogen compounds in the oils from different area of the maling oilfield increase with the decrease of depth from yan 10 to yan 4 5 subsections showing vertical migration of oil to the reservoirs the homogenization temperature of fluid inclusions in the reservoir rocks exhibited two peaks reflecting the two stages of oil migration and accumulation the migration pathways include fluvial sand bodies and unconformity surfaces the migration driving force was likely the capillary pressure and the abnormally high strata pressure in the mesozoic sequences

eocene arc continent collision in new caledonia and implications for regional southwest pacific tectonic evolution new caledonia preserves evidence that constrains models for the tectonic evolution of the southwest pacific region onland geology reflects four main tectonic phases 1 early mesozoic development of subduction related terranes and their accretion to the gondwana margin 2 cretaceous passive margin development and sea floor spreading during the gondwana breakup 3 foundering of an oceanic basin and the eocene arrival of thinned gondwana margin crust at a southwest facing subduction zone resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast and 4 detachment faulting during extensional collapse resulting in unroofing of metamorphic core complexes the last phase explains supposedly anomalous metamorphic gradients in the northeast of the island

north palawan block philippines its relation to asian mainland and role in evolution of south china sea the island of mindoro the northern part of palawan island and the reed bank area southwestern philippines together constitute a continental fragment the north palawan block lying within an island arc oceanic setting the permian to paleogene rocks of these areas indicate a geologic origin and history for the block contrasting with that of the rest of the philippine archipelago these rocks also suggest that the north palawan block once occupied a pre drift position contiguous with the south china mainland four prominent pre neogene regional unconformities are recognized both onshore and offshore the china mainland in taiwan and in the north palawan block the synchrony of these unconformities and the facies relation of the unconformity bounded sedimentary units strongly suggest a common pre neogene history for all these areas by contrast an important regional unconformity occurring at the top of the middle miocene throughout the palawan area is absent from the asian mainland extension in the south china sea basin since the mesozoic which has separated the north palawan block from the asian mainland has been approximately uniform from west to east however there is strong evidence to suggest that this extension has been achieved by temporally separated phases of continental crustal attenuation and more recent sea floor spreading from the foregoing observations and using the most recent magnetic spreading anomaly data for the south china sea a suite of palinspastic reconstructions has been prepared which shows the evolution of the south china sea area from the late triassic to the pliocene the reconstructions illustrate 1 the convergent continental margin setting of the north palawan block during much of the jurassic and cretaceous 2 the late cretaceous inception of the philippine island arc system 3 the subsequent counter clockwise rotation of the arc system from the late eocene onward 4 the paleocene to middle miocene opening of the south china sea and 5 the early to middle miocene collision between the north palawan block and the palawan subduction system

fractal analysis of tight shaly sandstones using nuclear magnetic resonance measurements assessing quantitatively the microscopic pore structures of porous rocks including irregularities of pore shapes and pore size distributions is becoming one of the most challenging efforts nuclear magnetic resonance nmr measurements were used to provide insights into the pore geometry pore size and shape and pore connectivity of the chang 7 tight shaly sandstones in situ permeability 0 1 md in ordos basin the incremental transverse relaxation time t2 distributions for the 100 brine saturated samples display unimodal and bimodal behaviors presenting a geometrical arrangement composed of small to large pore size domains the nmr parameters such as bulk volume irreducible bvi capillary and clay bound water free fluid index ffi movable water the value of t2 separating the bvi from ffi the amplitude weighted mean on a logarithmic scale t2gm and the value of t2 that shows the highest frequency on the t2 spectrum t2peak for each sample were determined then the fractal theory was adopted to quantitatively express the complexity and heterogeneity of the sandstones the results show that only minor primary intergranular porosity remains and variable amounts of micropores and secondary intragranular porosity with poor connectivity occur in the chang 7 tight shaly sandstones assuming spherical pores a new model to calculate the fractal dimension of pore structure from the nmr t2 distributions is proposed the fractal dimensions of all the samples are calculated and the accuracy of the proposed model is verified by the regression coefficients the microscopic pore structures are heterogeneous in these tight sandstones according to the high value of fractal dimensions micropores are the primary causes of heterogeneity in tight sandstones and samples with unimodal t2 distribution behaviors and high content of short components have the highest fractal dimension and heterogeneity the calculated fractal dimension is strongly correlated with t2peak and t2gm therefore the fractal model proposed in this study can be used to calculate the fractal dimensions and evaluate the heterogeneities of the porous rocks satisfactorily the fractal model proposed in this study helps to quantitatively assess the pore structures of tight sandstones using nmr measurements

paleomagnetism of palawan philippines abstract paleomagnetic studies have been carried out on palawan and on the island of busuanga to the north results from the cretaceous espina basalts of the calatuigas ophiolite in the south palawan block spb pass a fold test yield normal and reversed directions with a magnetic intensity and af demagnetization characteristics consistent with a primary trm the mean direction is 293 9 and an inclination of 5 8 with a k of 37 7 and an 95 of 12 6 this suggests that these ophiolites have moved northward and rotated counterclockwise by 66 13 with respect to the geocentric axial dipole gad field it also suggests that they were obducted from the south paleomagnetic directions from the jurassic busuanga cherts and the cretaceous guinlo formation from the island of busuanga in the north palawan block npb and from the guinlo on the main island of palawan are similar fail regional fold tests and have af demagnetization characteristics consistent with secondary magnetization their inclinations are statistically indistinguishable at a 95 significance level but variation in declination suggests differential local rotation about a vertical axis the paleolatitude is comparable to that of regions of pervasive cretaceous remagnetization in the south china borderland and may reflect similar remagnetization consistent with the npb s proposed south china origin

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

rapid emplacement of the oman ophiolite thermal and geochronologic constraints in understanding of ophiolite emplacement requires knowledge of the elapsed time between igneous crystallization and intraoceanic thrusting and the rate and duration of that thrusting hornblende 4oar 39ar ages demonstrate that the igneous oceanic crust in oman crystallized and cooled to 825 k in 1 2 m y hornblende ages from metamorphic rocks and from cross cutting dikes require that the basal metamorphic thrust fault beneath the ophiolite also cooled below 825 k in 1 2 m y motion along the sole thrust accounted for 200 km of displacement at a rate of 100 200 mm yr on the basis of age relationships and thermal considerations we favor a two stage model for the initial stages of samall ophiolite emplacement intraoceanic thrusting over 2 m y old lithosphere at 150 km m y parallel to a spreading ridge for 1 2 m y followed by equally rapid and brief thrusting over cold and old lithosphere preservation of the samail ophiolite is a direct result of its young age and positive buoyancy at the time of ocean closure and we propose that all ophiolites that originated near spreading centers and were emplaced onto continents were young at the time of intraoceanic thrusting

lacustrine basin unconventional resource plays key differences abstract there has been a revival in hydrocarbon source rock characterization and development associated with growing interest in unconventional resources where these fine grained organic rich rocks act as both source and reservoir to date the exploration focus on shale reservoirs has been largely on marine systems lacustrine source rocks for conventional resources are geographically important dominating regions such as china indonesia and brazil s resource base however they have been generally untested for unconventional resources there are a number of key differences in the nature of these hydrocarbon systems that should be considered when assessing whether lacustrine systems may represent future unconventional opportunities in areas where the conventional resource base is dominated by lacustrine sourced oil among the key differences between these depositional systems is the greater sensitivity to high frequency climatic variability within lacustrine systems lacustrine systems are highly sensitive to changes in the balance between precipitation and evaporation which may lead to rapid changes in lake level potentially exceeding 600 m these changes in depositional conditions are geologically rapid and may occur over periods of thousands of years such changes can reduce the areal extent of potentially thick source rock intervals to only those portions of a basin where a permanent deep lake was present thus the core unconventional target area may be geographically limited compared with their marine counterpart although potentially areally limited a review of many lacustrine source rocks suggests that their thicknesses are often significantly greater than marine source rocks an examination of the more distal portions of lacustrine systems where better source rock potential is present reveals that there is generally limited connectivity between source and conventional reservoir in these settings such as the wind river basin waltman shale the hydrocarbons remain trapped within the shales potentially leading to over pressured hydrocarbon charged systems such conditions suggest that although areally limited viable unconventional targets may exist if suitable reservoir conditions are present finally the character of the oils produced is different in these settings with lacustrine oils being waxy and displaying different hydrocarbon generation and cracking kinetics high wax oils display distinct flow characteristics being more viscous and may offer different production challenges than their non waxy marine equivalents additionally differences in their cracking kinetics may indicate that the timing of gas generation for shale gas plays may differ significantly from marine systems

models for dynamic evaluation of mudstone shale cap rocks and their applications in the lower paleozoic sequences sichuan basin sw china abstract the estimation of the sealing capability of cap rocks dynamically is one of the fundamental geological problems that must be resolved in petroleum exploration in this paper a porosity capillary pressure p c method was used to estimate the sealing capacity during cap rock burial and a permeability capillary pressure k p c plus over consolidation ratio ocr method to estimate the sealing capacity during uplift based on 120 capillary pressure porosity measurements a p c mathematical model has been established for the burial phase by analyzing the permeability data measured from 12 mudstone shale samples from different stratigraphic intervals under step loading conditions a permeability confining pressure k p mathematical model has been constructed moreover capillary pressure permeability data measured from 141 mudstone or shale cap rocks have been used to establish a k p c mathematical model for seal capacity evaluation during uplift additionally the ocr of mudstone or shale was calculated from the results of reconstructed burial and uplift histories these mathematical models were used in case studies in the sichuan basin south china the results indicate that capillary pressure p c is inadequate in evaluating sealing capacity of cap rocks but the combination of parameters p c and ocr works well the agreement between calculated and measured values shows the effectiveness and reliability of the models for dynamic estimation of the sealing capacity of mudstone shale cap rocks established in this study

middle oligocene oceanic crust of south china sea jammed into mindoro collision zone philippines mindoro island south of luzon philippines is a complex junction between the manila trench and the collision zone of the north palawan block with the western philippines mobile belt middle oligocene ophiolites recognized in this suture are coeval with the oldest magnetic anomalies of the south china sea basin these ophiolites are part of a complex pile of terranes thrust above the north palawan block at the lower middle miocene boundary these ophiolites are interpreted as fragments of south china sea oceanic crust jammed between two distinct continental blocks during the counterclockwise rotation of luzon

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

geodynamic evolution of the taiwan luzon mindoro belt since the late eocene abstract the structural framework of the taiwan luzon mindoro belt or festoon is described following three major transects the luzon transect with active subduction and active island arc the taiwan transect with active collision the mindoro transect with active subduction and inactive collision based on this geological study and on available geophysical data a model for the geodynamic evolution of this portion of the philippine sea and eurasia plates boundary is proposed in a succession of reconstructions between the late eocene and the present the major geodynamic events are 1 1 beginning of the opening of the south china sea s c s in lower oligocene times contemporaneous with obduction of the zambales and angat ophiolites on luzon 2 2 subduction of a mesozoic oceanic basin along the proto manila trench from the upper oligocene to the lower miocene 3 3 obduction of the south china sea oceanic crust onto the chinese and reed bank calamian passive margins in middle miocene time 14 15 ma related to a major kinematic reorganization end of opening of the s c s 4 4 beginning of collision between the luzon microblock and the two margins of the s c s in the upper miocene 7 ma collision is still active in taiwan whereas it stopped in mindoro during the pliocene

resource potential and core area prediction of lacustrine tight oil the triassic yanchang formation in ordos basin china unlike liquid rich hydrocarbons in marine shale systems in north america the triassic yanchang oil is preserved in tight sandstone reservoirs deposited in a lacustrine setting the tight reservoir covers an area of 30 000 km2 11 600 mi2 and is characterized by ultralow permeability 0 001 1 00 md 0 001 10 3 1 00 10 3 m2 a low subsurface pressure coefficient 0 6 0 8 and low single well yield several tons 10 40 bbl to 10 tons 70 bbl per day the reservoir also features a high content of quartz feldspar and carbonate averaging 70 80 and low crude oil density of 0 84 g cm3 36 5 api with an oil saturation of approximately 60 80 for the first time this study employs the assessment of petroleum in place resources based on the genesis and statistics predicting method gspm and estimated ultimate recovery method for the tight oil in the ordos basin the advantage of gspm over previously reported methodologies is the suitable combination of genetic and statistical methods to estimate proximally sourced tight oil the results show that the total in place resource potential of the investigated tight oil is approximately 42 26 108 t 295 82 108 bbl with an average abundance of 15 104 t km2 99 104 bbl mi2 the recoverable resources for the 50 probability of the chang 7 tight oil accumulation is 3 11 108 t 21 77 108 bbl in the ordos basin the top two grades of the chang 7 tight oil core area cover the total area of three layers comprising 12 745 km2 4921 mi2 with 22 51 108 t 157 57 108 bbl of in situ resources furthermore the four most promising zones have been identified

models of lithospheric scale deformation during plate collision effects of indentor shape and lithospheric thickness abstract analogue models designed to test the effects of lithosphere thickness and indentor shape during continental collision indicate that strength and density differences between lithosphere types control structural vergence during collision models presented here include layers of putty and sand to form four three and two layer lithosphere types craton arc and oceanic equivalent respectively which collide during unidirectional shortening in most cases the stronger thicker four layer lithosphere does not deform but simply acts to bulldoze weaker material aside deformation concentrated in the thinnest layers consistently verges away from the indenting continent irrespective of indentor shape lateral strike slip component deformation occurs in the early stages of most models even with simple unidirectional shortening and is enhanced by highly oblique indentor shapes the effects of extrusion during collision tested by repeating models with and without a free edge which allows extrusion consistently indicate that with the ability to extrude structures are smaller and more numerous without extrusion fewer larger structures tend to develop two geological examples from the precambrian part of the tasman orogenic belt and the modern day collision at the leading edge of australia illustrate aspects of the models

high energy surf zone currents and headland rips at a geologically constrained mesotidal beach we analyze eulerian and lagrangian measurements of wave induced circulation collected during a 3 week field experiment at a high energy mesotidal barred beach with the presence of a 500 m headland and a submerged reef small changes in wave and tide conditions were found to largely impact circulation patterns three main regimes were identified depending on offshore wave obliquity 1 under shore normal configuration the flow was dominated by cross shore motions except for moderate waves at low tide with the presence of a quasi steady circulation cell on the reef 2 under shadowed configuration an onshore directed current flowing away from the headland and a weak oscillating eddy were present outside and inside the shadow region respectively 3 under deflection configuration a deflection rip flowing against the headland and extending well beyond the surf zone was present with activity maximized around low tide for moderate waves under 4 m oblique waves the deflection rip was active regardless of the tide with mean depth averaged velocities up to 0 7 m s 800 m offshore in 12 m depth with energetic low frequency fluctuations our results emphasize the ability of deflection rips to transport materials far offshore suggesting that such rips can transport sediment beyond the depth of closure this study indicates that a wide variety of wave driven circulation patterns can occur and sometimes coexist on beaches with prominent geological settings changes in the dominant driving mechanism can occur as a result of small changes in wave and tide conditions resulting in more spatially and temporally variable circulation than along open sandy beaches plain language summary most field experiments about wave induced circulation patterns have been conducted along open sandy beaches while experiments in geologically constrained environments are scarce we performed intensive field measurements at a high energy beach with the presence of a 500 m headland and a submerged natural reef three main circulation patterns were identified depending on the offshore wave obliquity for shore normal waves cross shore motions dominated the nearshore region while oblique wave configurations resulted in more complex horizontal circulation in particular under intense headland directed longshore current the flow was deflected seaward against the headland this deflection resulted in an intense seaward flowing jet deflection rip extending well beyond the surf zone edge particularly during storm conditions such findings highlight the ability of these deflection rips to dominate water and sediment exchanges between the nearshore and the inner shelf region our study further outlines the more spatially and temporally variable circulation patterns occurring along geologically constrained beaches compared to open sandy beaches ranging from small recirculating cells across the reef to a large deflection rip extending hundreds of meters beyond the surf zone

implications of paleomagnetic data on the collision related bending of island arcs paleomagnetic studies from the marianas central philippines ryukyus sulawesi fiji new hebrides all show major differences in the declination values observed from individual islands within the same arc comparable differences are not observed in the inclination values a simple plate tectonic model would predict that each island arc should experience the same rotation along its entire length as the plate moves around its rotation axis bathymetry from each of these arcs show that the differentially rotated segments of the upper plate occur in areas where the downgoing plate carries a feature such as a seamount chain rifted continental fragment or an island arc the coincidence of the bathymetric feature and the discordant paleomagnetic declination data support an earlier hypothesis of vogt 1973 that these features are buoyant zones on the downgoing plate which interact with the margin of the upper plate as a result of this interaction the upper plate boundary is locally deformed in addition to the paleomagnetic evidence other geologic and geophysical data from these areas suggest such interactions for example there appears to be a good correlation between the deflections in major structures around the collision zone and the paleomagnetic directions that are reported as this deformation proceeds eventually the stresses resulting from the collision may result in any of the following tectonic processes 1 slip line style strike slip faults allowing for the sideward extrusion of portions of the upper plate tapponnier et al 1983 2 changes in the polarity of the subduction zone 3 development of strike slip faults around the margin of the indenter or 4 reorganization of the entire plate margin in addition data from the marianas southern end of the ryukyu arc and the lau basin suggest that back arc basin development may result from the collision related deformation

philippine fault a key for philippine kinematics on the basis of new geologic data and a kinematic analysis we establish a simple kinematic model in which the motion between the philippine sea plate and eurasia is distributed on two boundaries the philippine trench and the philippine fault this model predicts a velocity of 2 to 2 5 cm yr along the fault geologic data from the visayas provide an age of 2 to 4 ma for the fault an age in good agreement with the date of the beginning of subduction in the philippine trench the origin of the philippine fault would thus be the flip of subduction from west to east after the locking of convergence to the west by the collision of the philippine mobile belt with the eurasian margin

sr isotopic composition of marbles from the puerto galera area mindoro philippines additional evidence for a paleozoic age of a metamorphic complex in the philippine island arc the sr isotopic composition of marbles from the puerto galera area mindoro philippines is compatible with either a tertiary or a paleozoic age the former is considered as unlikely because nonmetamorphic sediments of that age overlie the metamorphic complex this implies that the metamorphic complex does not represent the basement of the philippine arc but is an accreted terrane

the palaeozoic tectono metallogenic evolution of the northern tasman fold belt system australia interplay of subduction rollback and accretion abstract the tasman fold belt system in eastern australia provides a record of the palaeozoic geological history and growth of the australian continent along the proto pacific margin of gondwana inboard of an extensive and long lived subduction system the hodgkinson and broken river provinces represent prominent geological elements of this system and together form the northern tasman fold belt system geochronological age dating of the timing of gold formation in the amanda bel goldfield in the broken river province and the hodgkinson goldfield in the hodgkinson province provides constraints on the occurrence of a deformation and mineralisation episode in the late devonian early carboniferous integration of these newly obtained data with petrogenetic constraints and a time space evaluation of the geological evolution of the hodgkinson and broken river provinces as well as other terranes in the northern tasman fold belt system allows for the development of a geodynamic model for the palaeozoic evolution of the northern tasman fold belt system our model indicates that three cycles of extension contraction occurred during the palaeozoic evolution of the northern tasman fold belt system episodes of extension were controlled by rollback of the subduction system along the proto pacific margin of gondwana whereas episodes of contraction resulted from accretion following the arrival of positively buoyant segments i e micro continental blocks oceanic plateaus at the subducting trench our composite interpretative model on the geodynamic evolution of the northern tasman fold belt system integrates the timing of the development of mineral deposits throughout this part of the system and provides a significant advancement in the understanding of palaeozoic geodynamics along the margin of gondwana in northeast australia and allows comparison with the southern part of the tasman fold belt system

outcrop architecture of a fluvio lacustrine succession upper triassic yanchang formation ordos basin china abstract although several studies have considered the sedimentary facies of the upper triassic yanchang formation in terms of their hydrocarbon potential in the petroliferous ordos basin such studies have mostly interpreted subsurface data and few have systematically examined the detailed outcrop based anatomy of this succession this study characterizes a series of well exposed outcrop sections along an 80 km long e w oriented series of road cuttings in the southeast ordos basin to reconstruct the sedimentary architecture of a fluvio lacustrine succession and determine the principal controls that governed the style of accumulation and preservation the yanchang formation is divided into 10 depositional units chang 10 base to chang 1 top that record the sedimentary evolution of a series of large scale fluvial systems that constructed delta front and pro delta bodies as they entered a large interior draining lake detailed analysis of the internal architectures of the delta front bodies records the mechanism of growth of a large scale shallow water delta succession lacustrine subaqueous distributary channels are composed of 3 15 m thick sandstone fills such channelized bodies are highly elongate and many can be traced several kilometres such bodies can be shown to be commonly associated with thin bedded mouth bar and subaqueous interdistributary bay deposition the progradational architecture of the delta front elements is difficult to recognize on outcrop scale deposits of the chang 10 to 1 units record 4 major lacustrine transgressive regressive cycles during the late triassic transgressive events are signified by the widespread occurrence of 10 20 m thick oil shale prone intervals regressive events are signified by the progradational stacking towards the basin centre of sandstone prone facies associations mainly accumulated in fluvial channel delta plain and upper delta front environments the uppermost chang 1 interval records late stage filling of the lacustrine basin the transgressive regressive cycles equate to sequences that can be correlated across the region development of which was controlled by a combination of changes in the rate of tectonic subsidence the rate of sediment delivery from the basin margin hinterland and climate factors that were themselves influenced by intracontinental growth of the neighbouring qinling orogen

cretaceous tectonics and geological environments in east russia abstract by the late jurassic the northern part of the east asian continental margin was diversified principal structural constituents were the siberian or north asian craton bounded on the east by a miogeosynclinal fold belt a system of smaller ancient blocks and a collage of terranes that had been attached to the craton from the east and southeast at different times such a diverse structural environment caused variability of cretaceous landscapes and related sedimentary systems global processes of lithospheric plate interaction and related regional tectonic processes played a leading role in cretaceous environmental changes in the continental margin of east russia during the early cretaceous the oblique plate convergence produced a transform continental margin over a long period of time during the middle albian a collage of terranes were attached to the continental margin of east russia then during the late albian period the angle of convergence increased subduction resumed and a giant east asian volcanic belt formed along the continental margin this belt was morphologically represented by a chain of mountain ridges up to 3000 m thus creating a sublongitudinal tectonic and climatic zonation the active continental margin with a typical environmental arrangement of marginal seas island arcs the open sea persisted until the end of the cretaceous the late maastrichtian tectonics was mostly characterized by overall uplift of the region

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

polyphase tectonics at the southern tip of the manila trench mindoro tablas islands philippines abstract the southern termination of the manila trench within the south china sea continental margin in mindoro is marked by a complex polyphase tectonic fabric in the arc trench gap area onshore southern mindoro the active deformation front of the manila trench is marked by parallel folds and thrusts grading southward to n50 w trending left lateral strike slip faults this transpressive tectonic regime active at least since the late pliocene has overprinted the collision of an early miocene volcanic arc with the south china sea continental margin san jose platform the collision is postdated by deposition of the late miocene early pliocene elastics of the east mindoro basin the tectonic and geological framework of this arc which overlies a metamorphic basement and eocene elastics suggests that it was built on a drifted block of the south china sea continental margin

pre eocene synmetamorphic structure in the mindoro romblon palawan area west philippines and implications for the history of southeast asia the structure of the pre eocene rocks considered as the basement of the philippines has been investigated in the mindoro lubang romblon tablas sibuyan and north palawan areas in the former two areas the same pre eocene succession of units is recognized from top to bottom 1 a pre eocene olistostrome 2 an ophiolitic nappe 3 a schistose sequence pelites sandstones basic schists and marbles and 4 a gneissic unit the nature of the contact between the olistostrome and the underlying units is unclear but the ophiolite and the schistose sequence form two thrust sheets of oceanic origin thrust upon the gneissic unit that is considered a part of a continental basement called the west philippines block small scale structures show that the early deformation stage is characterized by a submeridian 0 n40 e lineation formed in greenschist to amphibolite facies conditions during the thrusting kinematic analysis show that the thrusting was from north to south in north palawan metamorphic rocks with similar microtectonic and kinematic characteristics are found they are overlain by a late jurassic olistostrome which is correlated with the olistostromes found in calamian north mindoro carabao and buruanga peninsula north panay the microstructural features and the presence of the olistostrome suggest that the north palawan mindoro tablas romblon sibuyan and carabao islands belong to the same north palawan block of hamilton 1979 which is a continental fragment rifted from asia in cenozoic times it is assumed that the western panay and zamboanga areas which are characterized by mesozoic ophiolites and metamorphic rocks also belong to the north palawan block all these islands experienced to some extent the same mesozoic geohistory the south verging thrusting is interpreted as the result of an oblique collision of the west philippines block with asia the contemporaneous left lateral strike slip faulting and the calc alkaline magmatism widespread along the chinese margin are also included in the geodynamic model

a new insight on the geometry of subducting slabs in northern luzon philippines abstract we used hypocentral and focal mechanism data in order to characterize the tectonic configuration of northern luzon and propose a model for describing the geometry of the subducted slab of the eurasian plate beneath the northern segment of the manila trench we took into consideration some of the observed bathymetric features i e the bend in the trench line of the manila trench at 20 n lat and the collision and subduction of an extinct mid oceanic ridge at 16 17 n lat and the intraplate deformation pattern in the north luzon ridge region in depicting a model that is consistent with most of the observed features and phenomena in the study area an earthquake catalog covering the period from 1619 to 1997 was used in studying the distribution of strain energy released while earthquakes covering the instrumental years 1963 1997 were used to analyze vertical distributions of earthquakes in sections we refined the location of some of the historical earthquakes using macroseismic data the inclusion of historical records despite their inaccurate locations could prevent misidentification of some regions as aseismic zones or gaps in seismicity especially along structures with long return periods a focal mechanism database that covers the period from 1963 to 1997 was used to decipher intraplate deformation pattern and subduction process of the slab the focal mechanism database consists of first motion solutions from previous authors and cmt solutions from harvard university seismicity strain energy release and focal mechanism maps and cross sections were drawn in order to have a three dimensional visualization of the geometry and stress regimes of seismogenic zones a new model of the subducted slab of the eurasian plate beneath the manila trench is proposed the model suggests the collision and subsequent partial subduction of a buoyant plateau at around 20 n lat to explain the sharp bend in the trench line the complicated deformation pattern on the overriding plate fronting the bend and the shallow dip of the subducted slab beneath this zone a tear in the slab is also inferred to be present as evidenced by the observed gap in strain energy release and the abrupt change in dip from shallow to steep south of 18 n lat the gap in seismicity and strain energy release 65 300 km depth at around 17 n lat may be used to infer the trajectory and location of the subducted extinct mid oceanic ridge mor the aseismic behavior is probably caused by the subducted ridge which is still hot and is deforming plastically this is supported by the heatflow data which shows high values along the extinct mor the subducted part of the mor may serve as the weakest zone where this tear could be localized the tear may also explain the cause of the abrupt termination of the eastern chain of volcanoes south of 18 n lat the above model which is a refinement of the model introduced by yang et al tectonophysics 258 1996 85 is consistent with the observed seismicity and deformation pattern observed bathymetric features spatial distribution and geochemical character of volcanism in northern luzon

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

characteristics and controlling factors of lacustrine tight oil reservoirs of the triassic yanchang formation chang 7 in the ordos basin china abstract tight sandstone oil reservoirs have received increasing attention in petroleum exploration and exploitation previous research concerning tight oil reservoirs has predominantly focused on marine basins however in china tight oil reservoirs are mostly distributed in lacustrine basins taking the tight oil sandstones of the yanchang formation chang 7 oil reservoir interval the chang 7 for short in the ordos basin as an example five factors are identified that control their formation and occurrence firstly three episodes of oil charging took place during the early cretaceous which were 142 139 ma 128 122 ma and 114 106 ma respectively continuous generation and episodic expulsion led to multiple episodes of oil accumulation secondly widely distributed source rocks toc 1 0 provide hydrocarbons to the chang 7 the distribution of tight oil was controlled by the outer boundary of the source rock distribution while the transition areas between generation expulsion centers were the accumulation and enrichment zones in the chang 7 thirdly with the favorable conditions for retained hydrocarbons massive continuous tight reservoir beds average porosity 7 6 and average permeability 0 15 md developed in the chang 7 capable of forming large scale successive tight oil reservoirs fourthly different source reservoir assemblages have different expulsion patterns and amounts which led to different charging degrees and sizes of tight oil accumulations type iii source reservoir interbeds will be the most favorable target for exploration and exploitation in the chang 7 ordos basin finally under the driving mechanism of non buoyancy migration and accumulation pressure differences between source and reservoir rocks pdbsr serve as the primary expulsion and migration force for crude oil during the main accumulation periods in the chang 7