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

climatically driven sedimentary cycles in the late miocene sediments of the pannonian basin hungary abstract by detailed cycle analysis of marginal mostly delta plain facies successions of pannonian sediments the frequency of water level changes of the late miocene pannonian lake hungary can be identified cycle analysis is presented with the object of defining the orbital record preserved in the strata we use the bed thickness as input data for our cycle analysis statistical analysis revealed a slow upward increase of both the frequency and thickness of sand beds in the boreholes resulting from infilling of the lake by a basinward migration of the marginal facies cycles of different order were detected in the sediments the higher order cycles are very close to or are equivalent with the milankovitch climatic cycles 19 ka caused by precession 50 ka caused by obliquity and 400 ka is the longer period of eccentricity the longer 1 m y cycle is very poorly developed here it is probably the analogue of the 3rd order global climatic cycle cycle analysis suggests that one of the main controlling factors of the water level changes of the pannonian lake was high frequency climatic oscillations the long term climatic changes only had a faint impact on the sediments the record of the 3rd order water level changes is very subtle our results show that the water level changes followed the rhythm of that of the eustatic changes but being asynchronous to them i e at high sea level stage the pannonian lake level was low and vice versa

sequence stratigraphy in lacustrine basins a model for part of the green river formation eocene southwest uinta basin utah u s a abstract in the middle green river formation of central nine mile canyon uinta basin utah several lacustrine dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences these lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences two types of sequence boundary are identified type a sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or rarely parallel unconformity and they typically juxtapose amalgamated braided fluvial channel sandstone late lowstand systems tract onto the profundal oil shale they also bound depositional sequences that show a distinct asymmetry being dominated by transgressive systems tracts 5 80 m thick highstand systems tracts are less than 4 m thick and may be removed completely by erosion on overlying sequence boundaries other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type b sequence boundaries type a sequence boundaries mark pronounced base level falls following times when the uinta lake had merged with a lake in an adjacent basin to form a much deeper lake such merging permitted the establishment of a new threshold at higher elevation following lake level balancing type b sequence boundaries are interpreted as marking base level falls from a barely merged lake or a lake that had an outflow over a 200 m stratigraphic thickness type a sequence boundaries are more common upsection indicating that with time a pluvial climate became more pronounced or that the adjacent lake was more easily filled type a sequence boundaries also become angular rather than parallel unconformities upsection suggesting increased tilting of the basin margin over time

lithogeochemical patterns related to sedex mineralization sudbury basin canada abstract distal sediments stratigraphically equivalent to sedex zn cu pb deposits at the base of the proterozoic onwatin argillite formation sudbury basin are depleted in s and enriched in mn occurring as kutnohorite manganosiderite and spessartine and in ba in the form of the k ba feldspar hyalophane fluid inclusion data indicate deposition of the distal sediments at 125 c and of the sedex carbonate gangue at 170 c the overlying onwatin argillites deposited at 60 c are characterized by a distinctive pattern of s c org 0 36 indicative of diagenetic s alternating with s c org 0 36 probably reflecting episodic expulsion of s bearing fluids into the water column during the waning stages of hydrothermal activity similar to the s c org pattern are patterns of rhythmically alternating low and high zn pb as re ni and pd values in the onwatin argillite coinciding with the onset of hydrothermal activity 34 s values in pyrite decrease abruptly from 7 at the top of the onaping formation to 3 at the base of the overlying onwatin argillites 13 c values in the carbonate gangue of the sedex deposits 8 9 to 2 4 lie in or close to the range for magmatic carbon in contrast to values of 18 7 to 14 9 in carbonate derived by oxidation of organic carbon in the overlying and underlying rocks low 34 s values in the sedex deposits and basal onwatin rocks and enrichment of the onwatin argillite in s ni re and pd suggest derivation of these metals at least part of the s and possibly cu zn pb from the magmatic ni cu ores and or associated sudbury igneous complex which probably also provided the energy to drive the convective exhalative system responsible for the sedex mineralization the model implies potential for further sedex deposits along the 110 km of the onwatin onaping contact

fault control on depositional systems and sequence stratigraphic architecture in a multiphase rifted lacustrine basin a case study from the paleogene of the central bohai bay basin northeast china abstract the stratigraphic evolution of rift basins is complicated by out of phase displacement on boundary and intrabasinal faults and this analysis of paleogene strata in the central bohai bay basin of eastern china exemplifies this conundrum the spatial and temporal distribution of depositional systems and sequences in the central bohai bay basin are evaluated by using seismic reflection data in conjunction with drill cores and well logs three second order composite sequence boundaries are identified on seismic profiles on the basis of truncations below and onlap relationships above and by abrupt changes abrupt changes in gamma ray values on well logs composite sequences are comprised of third order sequences identified as distinctive seismic packages variations in thickness and distribution of third order sequences are consistent with out of phase displacement of boundary and intrabasinal faults which resulted in migration of depocenters in space and time a range of depositional systems are recognized including fan delta braid delta river delta sublacustrine fan and shallow and deep lacustrine during rift climax stages lowstand fan deltas developed on the hanging wall adjacent boundary faults to the north braid deltas on the footwall ramps to the south and sublacustrine fans in the central basin following transgression highstand braid deltas prograded from the north and south whereas river deltas during the late stages of basin fill both tectonic activity and climate were important controls on accommodation and the balance between sediment supply and accommodation determined the sedimentary architectures faulting uplift and erosion as well as fault block rotation controlled the formation of sequence boundaries and sequence geometries whereas variations in sediment flux can be attributed to climate changes high quality reservoirs are associated with deltaic channel fill and sublacustrine fan sandstones intrabasinal faults provided pathways for oil migration whereas prodeltaic lacustrine mudstones are source rocks as well as seals this study demonstrates that the spatial and temporal distribution of deposystems in rift basins in general requires an understanding of the history of boundary and intrabasinal faults within these compartmentalized basins

fluid flow and related diagenetic processes in a rift basin evidence from the fourth member of the eocene shahejie formation interval dongying depression bohai bay basin china the purpose of this paper is to relate diagenetic processes in deeply buried sandstones in the fourth member of the eocene shahejie formation interval bohai bay basin china to pore fluid flow changes with progressive burial based on petrographic mineralogical and geochemical analysis distribution patterns of authigenic minerals are recognized that reflect 1 the sources and patterns of fluid flow and 2 fluid flow in an evolving open to closed system partial to extensive precipitation of calcite and dolomite at or near mudstone sandstone contacts during eogenesis was a result of large scale mass transfer between sandstones and adjacent mudstones this process was driven by steep diffusion gradients from adjacent mudstones in a relatively open geochemical system on the local scale support for this model is provided by large sulfur isotope fractionation between framboidal pyrite and precursor gypsum dissolution of feldspar grains and dissolution of nonferroan carbonate cements during early mesogenesis are spatially associated with quartz and ferroan carbonate cementation respectively this process was related to organic carbon dioxide expelled from adjacent source rocks and indicates a relatively open system during late mesogenesis dissolution of evaporitic cements related to thermochemical sulfate reduction tsr generated ankerite and nodular pyrite cements in adjacent pores a lack of sulfur isotope fractionation between parent anhydrite and late stage nodular pyrite during tsr supports a relatively closed fluid flow system because the velocities of pore fluid flow were low during mesogenesis large scale thermal convection and advection probably did not occur instead diffusion over short distances is inferred as the predominant transport mechanism for dissolved solids that were precipitated as other phases either in situ or in adjacent pores

seismic structure of the bohai bay basin northern china implications for basin evolution as part of an extensive seismic research program 33 portable broadband seismic stations were deployed along a line crossing the bohai bay basin northern china three teleseismic events were selected to constrain the seismic structure along a 280 km profile across the western edge of the basin we determined the basin structure that described the observed shear horizontal sh wave field the synthetic sh wave was calculated using a finite difference fd method with its computational domain localized in the basin area and input motions at the base of the model extrapolated from the displacement recorded at a nearby hard rock station synthetic seismographs calculated for the models match the observations well in both waveform and travel time numerical tests indicate that the structural features of the preferred models are well resolved the analysis of relations between structures and stratigraphic units along the cross sections allows multiple deformational events in the basin to be inferred in conjunction with a profile across the southern edge that has been presented previously by zhao et al 14 l zhao t y zheng w w xu modeling the jiyang depression northern china using a wave field extrapolation fd method and waveform inversion bull seismol soc am 94 2004 988 1001 the results reveal basin wide extension with local inversion features in the bohai bay basin d 2005 elsevier b v all rights reserved

depositional cycles and sequences in an organic rich lake basin eocene green river formation lake uinta colorado and utah u s a abstract early to middle eocene green river formation lacustrine deposits in the eastern portion of lake uinta formed in two subbasins the piceance basin and the uinta basin and represent mixed siliciclastic carbonate and organic rich lake deposits formed during the time of the eocene climate optimum the formation consists of organic rich and organic poor mudstone i e oil shale siliciclastic and carbonate formed in a shallow to deep tens of meters stratified lake environment lacustrine strata are characterized by three types of decimeter to meter depositional cycles 1 type 1 depositional cycle formed in marginal areas cycle type 1 starts with siliciclastic rich deposits passes upward into alternating carbonate shoal and microbial carbonate and is covered by mud to silt size sublittoral deposits in the deeper profundal zone of the lake two types of depositional cycles occur 2 type 2 depositional cycles start with lean oil shale and pass upwards into siliciclastic turbidites and are sharply followed by rich oil shale deposits 3 type 3 depositional cycles begin with evaporites and lean oil shale with evaporites that are sharply overlain by rich oil shale stacked depositional cycles form depositional sequences meters to tens of meters thick altogether ten upward deepening depositional sequences have been defined and are correlated over the douglas creek arch from the piceance basin into the uinta basin depositional sequences characterize significant changes in lake regime and are divided into periods of low rising and high lake that are separated by sequence boundaries transgressive surfaces and main flooding surfaces respectively these depositional sequences indicate that the two basins were most probably connected during most of the first part of the green river formation in the middle of the green river formation the arch acted as a partial sill between the two basins when thick marginal deposits formed at the arch in the later part of the green river formation profundal deposits covered the arch it is suggested here that the development of depositional cycles and depositional sequences in these lacustrine basins is strongly affected by climate changes and respective inflow i e during times of low inflow siliciclastic and nutrient input into the lake decreased in contrast the highest input of siliciclastics and nutrients into the lake occurred during increased and high inflow low runoff resulted in low lake level and is marked by thin marginal deposits and lean oil shale in the profundal area at times evaporite deposition could occur in the deeper part of the basin in the change to a wetter period increased runoff is marked along basin margins by sharp based sandstones in the profundal area rich oil shale sharply overlies lean oil shale the evolution of lake uinta went through uniform regional and climate changes characterized by 1 forming of highly cyclic units in the middle of the green river formation at the time when the douglas creek arch acted as a partial sill between the two lakes 2 an overall deepening upward trend and 3 filling of basins with siliciclastic deposits at the end of green river formation time depositional trends that occur both in the piceance basin and in the uinta basin also occur in the greater green river basin in wyoming therefore the regional correlation model for all three green river formation lacustrine basins has been suggested here in order to show how different basins with similar tectonic and climate background changes could be correlated with each other

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

tracing migration pathways by integrated geological geophysical and geochemical data a case study from the jx1 1 oil field bohai bay basin china tracing petroleum migration pathways is essential for predicting petroleum occurrence and reducing exploration risks associated with hydrocarbon charge but a difficult task because of rapid lateral and vertical facies changes in lacustrine basins an integration of geological geophysical and geochemical analysis is employed to investigate the origin of crude oil the carrier bed architecture and migration pathways from source to trap in the jx1 1 oil field liaodong bay subbasin bohai bay basin detailed geochemical studies suggest that three potential source rock intervals and exist in the liaodong bay subbasin and crude oil in the jx1 1 field was derived from the and source rocks the carrier beds from and source rocks to the trap were characterized using geophysical data the fan delta sandstone in the member has an immediate contact with source rock and served as dominant conduit for the expulsion and migration of oil generated from source rock the braided delta sandstones overlying the source rock served as dominant conduit for sourced oil the focusing of petroleum migration pathways and the merge of migration pathways in and sandstones account for the accumulation of the jx1 1 field and the mixing of and sourced oil in the field this study suggests that the distribution of permeable sandstones and their stratigraphic contact with the source rocks are key for petroleum migration and occurrence and integration of geophysical geological and geochemical studies provide an effective way to trace petroleum migration pathways

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

the utilization of sequence stratigraphy in reservoir geology initial applications of sequence stratigraphy focused on basin analysis and exploration problems as finer scale studies were conducted using well logs and outcrops it has become possible to apply the concepts to improving reservoir performance investigations of the fine scale sequence stratigraphy of carbonates has led to its application to enhance production in the complex paleozoic carbonate reservoirs of the permian and paradox basins studies of coastal plain and shallow marine sediments in the colorado plateau and alberta basin has led to effective utilization in alberta basin reservoirs outcrop of and subsurface investigations of fluvial and deltaic sediments in the north sea has improved performance of jurassic reservoirs in the north sea geophysicists are refining statistical and numerical techniques for defining the seismic facies within reservoirs in indonesia africa and the gulf of mexico several sequence stratigraphic concepts are available for application e g genetic sequences t r sequences forced regressions etc allowing the data to speak for itself rather than slavish adherence to only one theory has greatly improved the utilization of sequence stratigraphy at the reservoir level

anatomy of a lacustrine stratigraphic sequence within the fourth member of the eocene shahejie formation along the steep margin of the dongying depression eastern china a comprehensive study on rift stratigraphy requires a solid understanding of sequence architecture along the steep margins of rift basins this study analyzes an eocene lacustrine sequence along the steep margin of the dongying depression in eastern china through integrated core well log and three dimensional seismic analyses the lacustrine sequence is bounded by unconformities and their correlative conformities at the base and top and consists of three systems tracts namely an early expansion systems tract eest late expansion early contraction systems tract leecst and late contraction systems tract lcst which record a lake expansion contraction cycle these systems tracts differ in thickness and development of depositional systems the eest is the thickest and contains well developed marginal and basinal fan systems with an overall retrogradational stacking pattern the well developed fan systems are the most striking features within the sequence the leecst is the most widespread and contains dominantly profundal sublittoral deposits the lcst is the thinnest with poorly developed fan systems and is characterized by significant erosion by fluvial incision the variable thickness and development of depositional systems in the three systems tracts are the responses to the interplay of sediment supply and accommodation space accommodation space establishes the framework for sedimentary infill and sediment supply determines spatial distribution and temporal evolution of depositional systems within each systems tract this study provides a lake expansion contraction scheme to divide a lacustrine stratigraphic sequence into systems tracts and highlights the feasibility of applying this approach in studying sequence stratigraphy along the steep margin of a lacustrine rift basin the results also provide understandings for the development distribution and evolution of depositional systems and their controlling factors along the steep margin of other rift basins in the world

depositional and diagenetic controls on deeply buried eocene sublacustrine fan reservoirs in the dongying depression bohai bay basin china abstract this paper investigates the reservoir potential of deeply buried eocene sublacustrine fan sandstones in the bohai bay basin china by evaluating the link between depositional lithofacies that controlled primary sediment compositions and diagenetic processes that involved dissolution precipitation and transformation of minerals this petrographic mineralogical and geochemical study recognizes a complex diagenetic history which reflects both the depositional and burial history of the sandstones eogenetic alterations of the sandstones include 1 mechanical compaction and 2 partial to extensive non ferroan carbonate and gypsum cementation typical mesogenetic alterations include 1 dissolution of feldspar non ferroan carbonate cements gypsum and anhydrite 2 precipitation of quartz kaolinite and ferroan carbonate cements 3 transformation of smectite and kaolinite to illite and conversion of gypsum to anhydrite this study demonstrates that 1 depositional lithofacies critically influenced diagenesis which resulted in good reservoir quality of the better sorted middle fan but poor reservoir quality in the inner and outer fan lithofacies 2 formation of secondary porosity was spatially associated with other mineral reactions that caused precipitation of cements within sandstone reservoirs and did not greatly enhance reservoir quality and 3 oil emplacement during early mesodiagenesis temperatures 70 c protected reservoirs from cementation and compaction

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

late syn rift sequence architecture and sedimentary evolution of a continental rift basin a case study from fulongquan depression of the songliao basin northeast china abstract as an important stage in continental rift basin evolution late syn rift stage is characterized by the combination of broad crustal subsidence and episodic pulses of extension sequence architecture and sedimentary filling process during this period present a certain particularity due to distinctive tectonic subsidence and variable influencing factors this paper analyzes sequence stratigraphy and sedimentary facies development and their evolution in the fulongquan depression a continental rift basin of the songliao basin and discusses the determinants influencing the sequence architecture and depositional systems evolution during late syn rift stage a major transition in the depositional systems from predominantly lacustrine and correlated depositional systems to fluvial floodplain settings was recorded in the evolution of basin fill this gradual and slow peneplanation is the final response to the decrease of differential subsidence the spatial and temporal variability of sedimentary evolution are mainly associated with specific growth history of the major boundary faults sequence stratigraphic units recognized in the fulongquan depression are likely corresponded to different episodic pulses of extension respectively each sequence can be further divided into a lowstand systems tract lst transgressive systems tract tst and highstand systems tract hst maximum differential subsidence and water deepening mainly occur in the lst the expanded tst and hst of each sequence tend to be developed in a broader thermal subsidence regime the depositional systems transition and detrital provenance changes usually occur in the hst throughout the late syn rift stage in addition to major changes of provenance systems tectonic movement is likely to be the main factor in controlling the variations of sediment supply with the decrease of tectonic activity the impact of climate changes and lake level fluctuations on basin filling tends to be increased

qualitative and quantitative prediction of diagenetic facies via well logs abstract drilled cores thin section petrography x ray diffraction xrd scanning electron microscopy sem routine core analysis rca and mercury injection capillary pressure micp tests were used to establish a predictable model for diagenetic facies and reservoir quality using well logs in sandstones of the paleogene dongying formation in nanpu sag bohai bay basin eastern china the results show that the sandstones are texturally and compositionally immature and have primary intergranular pores secondary intergranular and intragranular pores moldic pores and micro pores associated with diagenetic clay minerals the sandstones have undergone low to moderate mechanical compaction but a high degree of framework grain dissolution diagenetic minerals are dominantly of carbonates calcite dolomite and fe dolomite and clay minerals illite mixed layer illite smectite and kaolinite four types of diagentic facies are recognized tightly compacted carbonate cemented clay mineral filling and dissolution facies porosity permeability and oil saturation ranges among these diagenetic facies were determined from routine core analyses the diagenetic facies were then translated to conventional well logs by core log calibration and the well log expressions in terms of natural gamma ray neutron porosity bulk density sonic transit time and resistivity logs of various diagenetic facies were summarized the mineralogical composition obtained from the elemental capture spectroscopy ecs logs was then used for the diagenetic facies prediction the diagenetic facies predicted with the comprehensive conventional log analyses were combined with the ecs log profile and were calibrated with the xrd sem analysis and logging interpretation results for wells without ecs log the diagenetic facies can be quantitatively predicted by the mathematical calculations of reservoir quality index rqi via the gr ac and den log curves reservoir quality or oil bearing properties can be evaluated and predicted by translating the diagenetic facies to well logs

characteristics of the early cretaceous igneous activity in the korean peninsula and tectonic implications abstractthis study presents sensitive high resolution ion microprobe shrimp u pb zircon ages k ar ages and whole rock chemical and isotopic sr nd compositions of the early cretaceous igneous activity in western south korea the volcanics and plutons yield zircon u pb ages of ca 110 ma in the albian of the late early cretaceous k ar biotite and plagioclase ages are slightly younger ca 103 ma the geochemical signatures of the rocks are characterized by negative nb ta and ti anomalies relatively low nd t values between 15 91 and 9 36 and enrichment in light rare earth elements suggesting the effects of subduction related magmatism together with the sr and nd isotopic compositions of the intermediate to acid volcanics geochemical characteristics reflect a lower crustal magma source this albian event over the korean peninsula is related to early jurassic subduction and subsequent lithospheric delamination and or slab rollback after the early cretaceous amalgamation between the north c

stretching and subsidence rifting of conjugate margins in the north atlantic region subsidence on rifted conjugate continental margins around the north atlantic is analyzed to derive the amount and areal distribution of stretching in the crust and in the lower lithosphere during continental rifting study areas are the grand banks and orphan basin regions of the eastern canadian continental margin and the goban spur and galicia bank regions off western europe in all areas maps of synrift and postrift sediment thickness and bathymetry were used to derive maps of post and synrift subsidence a two layer lithospheric stretching model with independent amounts of stretching in the crust and in the lower lithosphere was assumed to be applicable with the rifting history approximated by several instantaneous episodes of extension this model was used to derive estimates of stretching at all points on a 0 05 geographical grid where subsidence values were available within the study regions the models are constrained with seismic measurements of crustal thickness the results imply that pure shear stretching predominates at a lithospheric scale while simple shear is more localized laterally and confined to the crust in places there is significant decoupling between crustal and mantle stretching near the continent ocean boundary final continental breakup may be localized on one side of the rift between conjugate margin pairs rather than symmetrically located total extension of the margins is compatible with that estimated from normal fault geometries and indicates that the continent ocean boundary has been extended up to 350 km seaward of its original position which should be considered in plate kinematic reconstructions

regressive and transgressive cycles in a rift basin depositional model and sedimentary partitioning of the middle jurassic hugin formation southern viking graben north sea abstract the jurassic hugin formation consists of shallow marine sandstones that belong to a significant hydrocarbon reservoir in the sleipner area in the norwegian north sea the formation encompasses coarsening upward units of mouth bar and shoreface facies interpreted to record delta outbuilding during regression and fining upward units with tidal channel dune and tidal flat facies interpreted as part of an estuary environment during transgression the correlations reveal that the studied part of the hugin formation consists of 8 sequences each with a transgressive and a regressive unit representing the transgressive systems tract and the highstand systems tract respectively the sequences are stacked retrogradationally landward as a result of rapid tectonic subsidence and rifting of the viking graben rifting led to the development of an elongate graben where tidal currents were amplified wave action damped and longshore drift as sediments supply reduced or absent lowstand and forced regressive systems tracts are not identified and their absence is interpreted to reflect suppression of relative sea level falls in a rapidly subsiding basin where the basin subsidence rate outpaced any potential fall in eustatic sea level through facies interpretation and sequence stratigraphic correlations between wells these regressive and transgressive units are shown to exhibit characteristic thickness trends in the form of sigmoidal shaped wedges stacked in an offset manner in a landward to basinward orientation these thickness trends illustrate sediment partitioning within the sequences and are explained by the relationship between accommodation versus sediment supply in terms of mass balance during regression the focus of sedimentation was pushed basinward and during transgression it was pushed landward as sediments were trapped there the mapping of these sequence stratigraphic units serves as input to reservoir models and to help increase recovery and identify new exploration targets

microbially induced dolomite precipitates in eocene lacustrine siliciclastic sequences in the dongying depression bohai bay basin china evidence from petrology geochemistry and numerical modeling this study investigates the origin of dolomite by examining thick lacustrine sequences of evaporites mudstones and deep water sublacustrine fan sandstones in the lower unit of the fourth member of the eocene shahejie formation es4x in bohai bay basin china this petrographic geochemical and numerical modeling study recognizes evidence for microbially mediated dolomite precipitates in the es4x sandstones including the following 1 spherical or elliptical dolomite aggregates consisting of submicrometer sized crystals 2 negative 13cvpdb vpdb refers to vienna peedee belemnite values of the dolomite cements 6 56 to 3 35 3 relatively low precipitation temperatures of dolomite cements 39 c 65 c 102 f 149 f based on 18ovpdb values from 8 76 to 4 65 and 4 negative 34svcdt vcdt refers to vienna canon diablo troilite values of associated framboidal pyrite 3 9 to 5 7 with respect to an anhydrite precursor 21 2 to 37 8 one dimensional reactive transport modeling incorporating biodegradation kinetics was conducted to evaluate the link between biodegradation of organic matter and geochemical reactions of inorganic minerals during microbial sulfate reduction msr microbial metabolism in the model creates favorable geochemical conditions for dolomite precipitation by increasing ph carbonate alkalinity and mg2 ca2 ratio the modeling results reproduce petrographic observations associated with the msr process and indicate that the kinetics of microbial growth can significantly modify the geochemistry of simulated waters and enhance microbially mediated dolomite precipitation therefore this study illustrates the effect of msr in dolomite precipitation in a semiclosed and reducing continental lacustrine basin

fan deltas and braid deltas varieties of coarse grained deltas two types of coarse grained deltas are recognized fan deltas and braid deltas fan deltas are gravel rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland they occupy a space between the highland usually a fault bounded margin and the standing body of water in contrast braid deltas here introduced are gravel rich deltas that form where a braided fluvial system progrades into a standing body of water braid deltas have no necessary relationship with alluvial fans as exemplified by fluvioglacial braid deltas braid deltas have previously been classified as fan deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different braid deltas are a common present day geomorphic feature and are abundant in the geological record fan deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems the shoreline and subaqueous components of both are similar fan delta sequences have a subaerial component that is an alluvial fan facies comprising interbedded sheetflood debris flow and braided channel deposits fan deltas produce small a few tens of square kilometres wedge shaped bodies of sediment commonly displaying high variability in paleocurrent patterns and abrupt changes in facies the deposits are generally very coarse grained with large out sized clasts very poorly sorted matrix rich polymictic heterolithic partially cemented by penecontemporaneous carbonate and have low porosity and permeability braid deltas in contrast have a subaerial component consisting entirely of braided river or braidplain facies their deposits display better sorting roundness and clast orientation than do fan delta sediments they lack a muddy matrix they display size grading and bar migration they commonly have a sheet geometry with high lateral continuity tens to hundreds of square kilometres and they exhibit moderate to high porosity and permeability valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse grained deltaic systems are not differentiated

late quaternary high resolution sequence stratigraphy of an active rift the sperchios basin greece an analogue for subtle stratigraphic plays the sperchios basin is an active asymmetric graben bounded to the south by a major border fault system with major fault segments typically 20 30 km long the basin is dominated by a major axial fluvio deltaic system which enters the partially enclosed maliakos gulf to the east lateral sourced depositional systems within the basin comprise hanging wall and footwall derived alluvial fans and a narrow coastal plain along the footwall scarp bordering the maliakos gulf high resolution seismic data from the maliakos gulf reveals three late quaternary progradational parasequences sourced from axial and lateral depositional systems with a regional late pleistocene transgressive surface dated at circa 10 ka bp within the maliakos gulf differential subsidence of the late pleistocene transgressive surface indicates marked variation in subsidence from 2 4 m ka sup 1 at fault segment centers to 0 8 m ka sup 1 at segment boundaries the geometry and internal variability of each parasequence is controlled by the interplay of the local accommodation development and fluctuations in sediment supply and climatic conditions the sperchios rift provides a modem analogue for subtle stratigraphic plays within ancient extensional basins the study of controls on sediment source and transport patterns within active rifts has refined our appreciation of the controlsmore on potential reservoir distribution and geometries less

sequence architecture depositional systems and controls on development of lacustrine basin fills in part of the erlian basin northeast china sequence architecture and depositional systems of a jurassic cretaceous lacustrine rift succession in the wuliyashitai subbasin and erlian basin in northeastern china were investigated using seismic profiles complemented by well logs and cores five second order or composite sequences are identified on the basis of basin scale unconformities constituent third order sequences are defined by unconformities along the basin margins and correlative conformities within the central basin lowstand transgressive and highstand systems tracts are separated by major lake flooding surfaces depositional systems identified in the basin include alluvial fan incised valley fan delta braid delta and sublacustrine fan three types of lacustrine sequences consisting of distinctive depositional systems formed during different tectonic stages 1 alluvial shallow lacustrine sequences type a developed during the initial rifting stage 2 shallow lacustrine to deep lacustrine sequences type b formed during the early and late periods of rifting and 3 deep lacustrine sequences type c developed in response to rapid tectonic subsidence during the middle maximum rifting stage uplift following each rifting episode related to changes in the paleostress field appears to have been the major control on the formation of high order sequence boundaries second order and some third order sequences block rotation coupled with lake level fluctuations controlled the formation of most third order sequence boundaries forward simulation modeling suggests that development of different lacustrine sequence types can be related to a balance between tectonic subsidence and sediment input begin page 2018 deltaic sandstone bodies and incised valley fills along the hinged margins within the shallow lacustrine and deep lacustrine sequences and sublacustrine fan sandstones in the central basin are the economically most important reservoir sandstones in the basin fan delta deposits along the escarpment margin constitute another potential reservoir type

high resolution stratigraphy of an underfilled lake basin wilkins peak member eocene green river formation wyoming u s a abstract lakes tend to respond noticeably to minor changes in sediment and water balance driven by climatic tectonic or geomorphic processes this unique behavior of lacustrine basins can provide a high resolution record of geologic processes within the continental setting far from the globally averaged record of marine strata the wilkins peak member of the eocene green river formation in wyoming usa is dominated by aggradation of repetitive sedimentary facies successions recording distinct lacustrine expansions and contractions these lacustrine cycles consist of up to four successive facies associations littoral profundal sublittoral palustrine and salt pan because they comprise disparate facies that may never have been simultaneously deposited in the basin wilkins peak member cycles are non waltherian successions that do not readily equate to any established sequence stratigraphic unit the completeness of the stratigraphic record in the wilkins peak member varies continuously across the basin at least 126 cycles are present in the erda white mountain 1 core near the basin depocenter whereas only about one third as many are recognizable 53 km north nearer to the basin margin cycle boundaries terminate northward by gradual amalgamation into palustrine facies reflecting the interplay between varying lake levels and a south dipping deposition gradient evidence for complete desiccation and hiatuses is commonplace even near the basin center a truly complete record may not be present anywhere based on recent 40ar 39ar geochronology of tuffs the average cycle duration in the white mountain 1 core is approximately 10 000 years however the true average duration is shorter due to the presence of lacunae and the time required for deposition of the thinnest cycles may have been less than 1000 years no external driving mechanism is presently known for eocene cycles of such short duration raising the possibility that they are instead autogenic cycles related to geomorphic instability of the surrounding landscape evaporite deposition corresponded closely in time and space to maximum differential subsidence suggesting that tectonic influences on drainage patterns and basin accommodation exerted a primary control differential accommodation was most pronounced during deposition of the lower wilkins peak member and became progressively less so after that time based on structural and stratigraphic observations a period of increased tectonic uplift commenced concurrent with deposition of the lower wilkins peak member

petroleum resources in the nanpu sag bohai bay basin eastern china the nanpu sag is an important secondary tectonic division of the bohai bay basin and has an area of 1532 km2 591 mi2 of which 1000 km2 386 mi2 has been explored near bohai recently exploration has gradually shifted from continental to beach to shallow marine settings with significant exploration breakthroughs having occurred in the nanpu 1 2 and 3 tectonic belts indicating good resource potential however a systematic resource assessment has yet to be performed which strongly restricts the exploration progress in this study we improved upon the pareto model and reevaluated the area s resource potential using two new methods in one method the traps are divided into several types including structural stratigraphic and buried hill traps to predict their individual resource potential and total resources of this area in the other method the normalized fluid potential is used to divide the area into several accumulation systems to calculate the resource potential the nanpu sag resources are estimated at 1 45 109 t 10 6 109 bbl which represents an increase of approximately 2 70 108 t 19 8 108 bbl compared with previous evaluations because of the increase in exploration maturity and information validation the main residual resource is distributed in beach to shallow marine settings the stratigraphic and buried hill traps present better resource potential using the trap type method such information can guide the direction of exploration and selection of potential traps

depositional systems and sequence architecture of the oligocene dongying formation liaozhong depression bohai bay basin northeast china the sequence stratigraphic framework and depositional systems of an oligocene lacustrine rift succession in the liaozhong depression of bohai bay basin in northeastern china were investigated using seismic profiles complemented by well logs and cores seven sequences are identified on the basis of unconformities on basin margins and correlative conformities in the basin center depositional systems are associated with systems tracts within sequences lowstand systems tracts are dominated by sublacustrine fans transgressive systems tracts are mainly composed of beach bar deposits and highstand systems tracts are characterized by deep lacustrine fan or braid delta deposits episodic tectonic movement was the principal factor that controlled the development of the sequences lake level changes resulting from climatic oscillations may have controlled the development of these sequences the balance between tectonic subsidence and sediment supply controlled the type of lake basin the bohai bay basin was a balanced fill basin in the early and middle stages of the dongying formation and evolved into an overfilled basin at the end of deposition of the dongying formation this study enhances the understanding of depositional system configuration and systems tracts in a typical rift basin and proposes that the most favorable sandstone reservoirs are developed in sublacustrine fan deposits relative lowstand sublacustrine fan deposits capped by relative highstand prodelta or deep lacustrine mudstones form the highest potential lithostratigraphic traps

sequence stratigraphy sedimentary systems and petroleum plays in a low accommodation basin middle to upper members of the lower jurassic sangonghe formation central junggar basin northwestern china abstract the lower jurassic junggar basin is a low accommodation basin in northwestern china because of low subsidence rates and a warm wet climate deposits of the central subbasin of the junggar basin formed from fluvial deltaic shallow lake facies sequence stratigraphy and sedimentary systems of the lower jurassic members of the sangonghe formation j1s were evaluated by observing cores interpreting wireline logs and examining seismic profiles two third order sequences were recognized in the strata the distribution of the sedimentary systems in the systems tracts shows that tectonic movement paleorelief paleoclimate and changes in lake level controlled the architecture of individual sequences during the development of the lowstand systems tract lst the intense structural movement of the basin resulted in a significant fall in the water level in the lake accompanied by rapid accommodation decrease braided rivers and their deltaic systems were also developed in the central junggar basin sediments carried by braided rivers were deposited on upward slopes of the paleorelief and braid delta fronts were deposited on downward slopes during the transgressive systems tract tst the tectonic movement of the basin was quiescent and the climate was warm and humid lake levels rose and accommodation increased quickly shoal lines moved landward and shore to shallow lake deposits sublacustrine fans and deep lake facies were deposited in shallow to deep lake environments during the highstand systems tract hst the accommodation no longer increased but sediment supply continued far exceeding accommodation hst deposits slowly formed in shallow lake to meandering river delta front environments relatively low rates of structural subsidence and low accommodation resulted in coarse grained successions that were fining upward deposits were controlled by structural movement and paleorelief within the lst to tst deposits in the central subbasin fine to medium grained coarsening upward successions developed during the hst the sand bodies of braid delta fronts on the downward slopes of the paleorelief in the lst and the sublacustrine fans in the tst became reservoirs for hydrocarbon accumulation petroleum plays have only been found in the sangonghe formation j1s located on structural ridges that consist of sand bodies comprising these sequences favorable conditions for petroleum plays in hst1 lst2 occur where the sand bodies have been fractured by faults and sealed by denudation and pinch out lines then overlain by deep lake mudstone in tst2 the favorable condition of the sand bodies within tst2 occurs where isolated sand bodies have been fractured by faults

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

rift related sedimentary evolution and its response to tectonics and climate changes a case study of the guaizihu sag yingen ejinaqi basin china abstract distinguished from most existing rift basin evolutionary models the succession of deep water deposits in the guaizihu sag were mainly developed during rift initiation instead of the greatest tectonic subsidence phase this paper focuses on the detailed analysis of rift related sequence stratigraphy and sedimentary evolution in this continental rift sag and discusses tectonic and climatic controls on filling patterns the deposits of the guaizihu sag can be ascribed to four major depositional systems alluvial fan and fan delta braided delta sublacustrine fan and shallow to deep lacustrine deposits they are in part contemporaneous and some succeeding each other forming five sequence units and corresponding substages of basin evolution i rift initiation ii early rift climax iii middle rift climax iv late rift climax and v late syn rift substages with the onset of fault movement and hot humid climate conditions the first substage is characterized by a number of poorly linked depocenters which consist of alluvial fan fan delta and deep lacustrine deposits with organic rich mudstones the second substage is associated with an enhanced activity of border faults and block rotation this unit is dominated by lacustrine deposits but fan or braided delta and sublacustrine fans also can be observed the third substage is marked by the maximum subsidence rate and shallow lakes fringed by fan and braided deltas the arid environment is likely to be the main factor controlling the lithofacies and filling characteristics of this unit during the fourth substage two early sub sags gradually converged to form a uniform one the relative tectonic quiescence and climate fluctuations sub humid to sub arid favored carbonate deposition the late syn rift unit which is dominated by fine grained deposits is a consequence of degradation of source area mostly tectonic this study shows that the effects of tectonics and climate on lacustrine sedimentation are intimately interwoven tectonism determines the sag structure stratigraphic architecture and spatial distribution pattern of depositional systems climatic conditions superimposed on tectonics tends to be the major control on sediment supply lithofacies types and sedimentary features

seismic reflection imaging of a major strike slip fault zone in a rift system paleogene structure and evolution of the tan lu fault system liaodong bay bohai offshore china the tan lu fault system in the liaodong bay bohai offshore china affords an exceptional opportunity to document the structural features of a major strike slip fault using two and three dimensional seismic reflection data as well as evolution of a strike slip fault developed coeval with a rift system the fault zone displays a relatively straight throughgoing trace longitudinally bisecting the rift valley it consists of positive and negative flower structures and en echelon folds in the south bay and three parallel flower structure systems northward the middle fault bifurcates northward into two semiparallel vertical fault strands to the north the west strand bends clockwise and merges with the east strand the stepping pattern and orientation of en echelon structures indicate right lateral sense and about n10 35e azimuth of slip the fault apparently accrued about 30 40 km 20 25 mi of post early eocene slip based on the current distribution of deformation zones and depocenters tan lu fault segments with clockwise and counterclockwise orientation relative to the regional slip direction are characterized by divergent and convergent structures i e restraining and releasing bends respectively waning of rifting eliminated the cause of a major restraining bend putting an end to development of associated convergent structures in the south bay area near the central north bay deformation occurred along major normal faults related to the basin rifting although a prominent feature reflecting regional strain partitioning the tan lu fault apparently was not a major factor in the paleogene opening of the liaodong bay basin and the larger north china rift basin

burial evolution of evaporites with implications for sublacustrine fan reservoir quality a case study from the eocene es4x interval dongying depression bohai bay basin china abstract eocene sublacustrine fan sandstones that developed in a rift basin are important tight gas reservoirs in the dongying depression bohai bay basin northeastern china two units of evaporites developed at the top and bottom of the lower unit of the es4 interval es4x consist predominantly of anhydrite with subordinate gypsum evaporite and related diagenetic processes greatly influenced reservoir quality 13 c values for micritic dolomite cements in es4x are depleted 7 45 to 2 57 due to microbial sulfate reduction msr under shallow burial conditions and this interpretation is supported by large 34 s fractionation between anhydrite and framboidal pyrite precipitation temperatures for micritic dolomite are calculated as 57 5 72 8 c anhydritization of gypsum probably occurred at 100 5 145 2 c during progressive burial as evidenced by homogenization temperatures of aqueous inclusions within anhydrite cements this process resulted in dehydration fractures within anhydrite cements that increased reservoir permeability by connecting isolated pores thermochemical sulfate reduction tsr probably resulted in dissolution of gypsum and anhydrite cements under relatively deep burial conditions ankerite cements are replaced by anhydrite cements and are enclosed by solid bitumen in es4x ankerite cements likely were derived from tsr as reflected in negative 13 c values 7 12 to 3 70 and high calculated temperatures 121 3 185 1 c dissolution by products e g saddle dolomite ankerite nodular pyrite related to tsr precipitated in adjacent pores a lack of significant 34 s fractionation between parent sulfate and nodular pyrite indicates that tsr occurred in a relatively closed system therefore dissolution of gypsum and anhydrite related to tsr contributed little to reservoir quality middle fan lithofacies with better sorting porosity and permeability than inner and outer fan lithofacies constitute high quality reservoirs in es4x