The study of sequence stratigraphy often focuses on shallow marine and shelf-edge regions,while research on deep-sea stratigraphic sequences remains relatively weak.This study,based on highresolution 3D seismic data a...The study of sequence stratigraphy often focuses on shallow marine and shelf-edge regions,while research on deep-sea stratigraphic sequences remains relatively weak.This study,based on highresolution 3D seismic data and drilling information,utilized sequence stratigraphy and seismic sedimentology as guidelines,and employed seismic interpretation methods to performed a division of deepsea stratigraphic sequences within the Romney 3D seismic survey area in the deep-water Taranaki Basin,New Zealand.Furthermore,it analyzed the characteristics of typical depositional systems and their associated controlling factors.The findings are as follows:(1)Based on seismic reflection termination relationships and seismic facies characteristics,four second-order sequence boundaries and nine thirdorder sequence boundaries were identified,resulting in the delineation of three second-order sequences and twelve third-order sequences in the basin.(2)Five seismic facies were recognized,corresponding to five typical sedimentary bodies:mass transport deposits(MTDs),deep-water channel,levee deposits,deltaic deposits,and pelagic deposits.However,due to the relatively thin sedimentary thickness of carbonate sediments,the seismic facies characteristics of carbonate sediments cannot be discerned in seismic data,but can be identified based on well data.Deltaic sediments mainly developed during the rift stage of the basin,while carbonate sediments formed during the transition from a passive to an active margin.Deep-water channel and levee deposits and MTDs emerged during the active margin stage,while pelagic deposits are ubiquitous in marine environments.(3)The uplift of New Zealand's interior and climate-driven erosion caused the resurgence of clastic sediments,which began to be transported to the deep sea,the seafloor topography would directly affect the movement path of sediment gravity flow,and sediment supply can affect the development and evolution of sedimentary systems.(4)Event deposits boundaries,such as erosional scour surfaces formed by channels and unconformities created by MTDs,can serve as boundaries for the division of deep-water stratigraphic sequences.This study proposes a method for delineating deep-water stratigraphic sequences using event deposits,particularly suitable under conditions where the influence of relative sea-level changes on deep-water deposits is relatively weak.This research not only enhances the understanding of deep-water depositional sequences but also provides a reference for studies on the evolution of deep-water deposition and its controlling factors in research areas with similar geological backgrounds worldwide.展开更多
In the Northern Himalayan region of Southern Xizang (Tibet),from the Lower Triassic to Upper Eocene 73 Sequences have been identified, with an average duration of 2.9 Ma;these can in turn be grouped into 24 super-Sequ...In the Northern Himalayan region of Southern Xizang (Tibet),from the Lower Triassic to Upper Eocene 73 Sequences have been identified, with an average duration of 2.9 Ma;these can in turn be grouped into 24 super-Sequences and 6 super-sequence sets. During Mesozoic and Paleogene, several large sea - level falls occurred in the Eastern Neo-Tethys. Among the recognized sea- level falls, the important ones include those at the ages of 255 Ma, 215 Ma,177 Ma, 138 Ma, 103 Ma and 68 Ma .Those at 239 Ma, 215 Ma, 157 Ma,80 Ma, 50Ma and 36 Ma are also significant. The third-order Sequences and sea-level cycles Probably reflect mainly global sea - level fluctuations, while the higher rank cycles seem more closely related to the basin evolution of the Neo-Tethys. Based on the study, six major periods have been suggested for ths tectonic evolution of the Eastern Neo-Tethys and the plates, i. e. the Pangea Period (Pre-Triassic), continental rifting Period (Triassic to Early Jurassic ), inter-continental sea Period (Middle Jurassic ), continental divergence period (late Middle Jurassic to Early Cretaceous ), continental convergence period (Late Cretaceous ) and the continental collision Period (Paleogene ). These major Periods can be further subdivided into eight stages according to the basin evolution. In each of the periods and Stages, Sequences and their boundaries show clear characters related to the tectonic background. The study indicater that the initial breakup of the Pangea along the Indus- Yarlung may have taken Place around 239 Ma. The Late Bathonian to Early Callovian seems to have been a critical time in the evolution of the Neo-Tethys, with the turning Point around 158 Ma. The blocks split from the northern margin of the Gondwana continual did not obviously drift away from the Indian Plate until Callovian .The oceanic crust subduction in the Neo- Tethys may have Started at 113Ma, while the contraction of the ocean probably began at 107- 103 Ma. The initial contact of the Indian Plate with the Eurasian plate may have taken Place around 80 Ma, with strong uplifting and thrushng in Late Paleocene.展开更多
This research uses both three-dimensional(3D)modeling and geologic well control to piece back together the architectural parts of the Late Cretaceous formations.The goal is to figure out the sizes,directions,locations...This research uses both three-dimensional(3D)modeling and geologic well control to piece back together the architectural parts of the Late Cretaceous formations.The goal is to figure out the sizes,directions,locations,and controls of the layers of the fluvial sandstone reservoirs.Sequence stratigraphy is essential for 3D reservoir modeling and petroleum geology understanding in the Bahga oilfield.The purpose of this work is to create a static model that shows the layers and facies distribution in the reservoir interval.We will use data from nine well logs and 22 seismic lines calibrated by the Abu Roash G Member reservoir core intervals to accomplish this.The petrophysical study discovered three parts in the Abu Roash G Member reservoir rock:channel fill that is affected by tides,channel fill that is dominated by tides(intertidal sands),and channel top with lenticular bedded sandstone.The model's findings point to the existence of an NNW-oriented sand body,which could be a prime location to produce hydrocarbons.The original oil in place(OOIP)is about 3,438,279 Stock Tank Barrels(STB),and the oil reserve reaches up to 1,031,484(STB).Sequence stratigraphic analysis using seismic and well log information(SB)reveals that the Upper Cretaceous AR/G reservoir of the Bahga field is characterized by third-and fourth-order stratigraphic sequences,which are constrained by three Maximum Flooding Surfaces(MFS)and two Sequence Boundaries.The integration of the derived geological model and sequence stratigraphic results can lower future extraction risk by identifying the locations and trends of the geologic facies with the necessary petrophysical properties for the hydrocarbon accumulations.展开更多
A Oilfield is the most representative mid to deep oil field in the Bohai Sea, with the main oil bearing intervals being the upper and middle Shahejie-3 sections of the Paleogene Shahejie Formation. By combining well s...A Oilfield is the most representative mid to deep oil field in the Bohai Sea, with the main oil bearing intervals being the upper and middle Shahejie-3 sections of the Paleogene Shahejie Formation. By combining well seismic analysis, the middle section of Shahejie-3 is divided into high-level system tract and forced lake retreat system tract, corresponding to the II oil formation and I oil formation, respectively. Using sequence stratigraphy methods, based on seismic profiles and drilling lithological cycles, the high stand system tract is divided into 5 stages of delta progradation. The first and second stages are high angle S-type progradation with large sedimentary thickness, the third stage is oblique progradation, and the fourth and fifth stages are S-oblique composite progradation;By combining seismic data, we characterized the large-scale (8 small-scale) progradation bodies of 5 periods, clarified the distribution characteristics of reservoir planes, and laid the foundation for the later exploration of oilfield potential.展开更多
Silicalites are extensively developed in the Liujiang Formation(Fm.)of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales.This stratigraphic combination represents a special sequen...Silicalites are extensively developed in the Liujiang Formation(Fm.)of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales.This stratigraphic combination represents a special sequence stratigraphy formed in special deep-water environments,which not only gives the shales unusual spatio-temporal distribution features,but also induces the shales in the Liujiang Fm.to frequently be rich in organic matter(OM).This study summarises the special deep-water sedimentary succession of the Liujiang Fm.,which is mainly distributed around synsedimentary faults,as well as establishing the sequence stratigraphic frameworks of the Liujiang Fm.in the west-east and southwest-northeast directions.Under the sequence stratigraphic frameworks,the spatio-temporal distribution features of the organic-rich shales of the Liujiang Fm.and the regional variations of the Liujiang Fm.were investigated.In addition,the rock components and OM occurrence states of the organic-rich shales were also observed and described in detail under the microscope.The results show that the organic-rich shales were formed temporally primarily during the third-order sea-level falling stage,developed spatially mainly on the east and west sides of the study area,as well as that the OM accumulation is closely related to tentaculitoids and seems to be influenced by a'biological pump'.展开更多
There are 9 major coal-accumulating periods during geological history in China,including the Early Carboniferous,Late Carboniferous-Early Permian,Middle Permian,Late Permian,Late Triassic,Early-Middle Jurassic,Early C...There are 9 major coal-accumulating periods during geological history in China,including the Early Carboniferous,Late Carboniferous-Early Permian,Middle Permian,Late Permian,Late Triassic,Early-Middle Jurassic,Early Cretaceous,Paleogene and Neogene.The coal formed in these periods were developed in different coal-accumulating areas(CAA)including the North China,South China,Northwest China,Northeast China,the Qinghai–Tibet area,and China offshore area.In this paper,we investigated depositional environments,sequence stratigraphy,lithofacies paleogeography and coal accumulation pattern of five major coal-accumulating periods including the Late Carboniferous to Middle Permian of the North China CAA,the Late Permian of the South China CAA,the Late Triassic of the South China CAA,the Early-Middle Jurassic of the North and Northwest China CAA,and the Early Cretaceous in the Northeast China CAA.According to distribution of the coal-bearing strata and the regional tectonic outlines,we have identified distribution range of the coal-forming basins,sedimentary facies types and coal-accumulating models.The sequence stratigraphic frameworks of the major coal-accumulating periods were established based on recognition of a variety of sequence boundaries.The distribution of thick coals and migration patterns of the coal-accumulating centers in the sequence stratigraphic framework were analyzed.The lithofacies paleogeography maps based on third-order sequences were reconstructed and the distribution of coal accumulation centers and coal-rich belts were predicted.展开更多
Three third-order sequences and about one hundred high-frequency cycles or Milankovitchcycles within the Late Permian Changxingian to Early Triassic Griesbachian are identified in theMeishan Section of Changxing, Zhej...Three third-order sequences and about one hundred high-frequency cycles or Milankovitchcycles within the Late Permian Changxingian to Early Triassic Griesbachian are identified in theMeishan Section of Changxing, Zhejiang Province, southern China, the candidate stratotype sec-tion of the global Permo-Triassic boundary, based on a detailed study of the biological,ecological and high-resolution allochthonous cyclic events, microfacies and depositional systems.Furthermore, the stacking pattern of the depositional systems across various Changxingian andGriesbachian sedimentary facies of the Lower Yangtze and the sequence stratigraphic frameworkare outlined with the Meishan section as the principal section. In this paper the habitat types offossil biota are applied to semiquantitative palaeobathymetry and the study of relative sea levelchanges.展开更多
The Lower Permian Shanxi （山西） Formation is one of the main gas-bearing stratio graphic units in northeastern Ordos （鄂尔多斯） Basin, China. Based on an integrated investigation of well logs, cores, and outcrop, ...The Lower Permian Shanxi （山西） Formation is one of the main gas-bearing stratio graphic units in northeastern Ordos （鄂尔多斯） Basin, China. Based on an integrated investigation of well logs, cores, and outcrop, we delineated the sedimentary facies of the lower member of the Shanxi Formation and divided the succession into three third-order sequences from base to top as SQ1, SQ2, and SQ3. The lower region of Shanxi Formation was deposited in the following sedimentary facies or subfacies： subaqueous braided channel, subaqueous interdistributary, mouth bar, swamp and shelf in the Daniudi （~z~=J~） Gas Field and braided channel, and shelf and lake at Heidaigon （~J） outcrop. Braided-river deposits form the lowstand systems tract （LST） in each sequence. Braided channels mark the sequence boundaries at Heidaigou outcrop. A shelf and lake depositional environment with dark gray mudstone forms the transgressive systems tract （TST）. The location where dark gray mudstone first appears above the braided channel marks the first flooding surface （FFS）, and the end of that marks the maximum flooding surface （MFS）. The highstand systems tract （HST） deposits are fine-grained sediments with an aggradational parasequence at Heidaigou outcrop and swamp coalbed in the Daniudi Gas Field. Mouth-bar sand bodies in braided delta front, which form the LST in each sequence, form excellent reservoirs in the Daniudi Gas Field.展开更多
The Lower Cretaceous strata in the Kuqa Basin in Xinjiang are marked by a set of arid red beds. Several types of sedimentary fades can be identified in this set of arid red beds: mudstones of the plaza and intracontin...The Lower Cretaceous strata in the Kuqa Basin in Xinjiang are marked by a set of arid red beds. Several types of sedimentary fades can be identified in this set of arid red beds: mudstones of the plaza and intracontinental sebkha, aeolian sandstones, sandy conglomerates of the intermittent river, conglomerates of the pluvial fan, etc. These types of sedimentary facies constitute a typical desert system. Therefore, the Cretaceous strata in the Kuqa Basin provide a favorable condition for studies of sequence stratigraphic divisions of the desert system. With the rise and fall of the base level of the sedimentary basin, cyclicity is clearly revealed in stratigraphic records, which helps the identification of the third-order sequences. Based on the cyclicity in stratigraphic records, 5 third-order sequences can be found in the strata of the Early Cretaceous in the Kuqa Basin. These sequences comprise a second-order tectonic sequence. The primary feature of these third-order sequences is of an upward-fining sedimentary succession formed by a succession of 'coarse sediments of the alluvial system-fine sediments of the lake system'. The result of this study shows that aeolian sandstones are the best reservoirs of natural gas in the Cretaceous strata in the Kuqa Basin, and that the Kela-2 gas field is the first large gas field dominated by aeolian sandstone reservoirs in China.展开更多
In South China four depositional sequences are recognized in the upper part of Upper Devonian and Tournaisian. They are named SQ0 SQ1, SQ2 and SQ3 in ascending order. SQ0 is Strunian (uppermost Devonian), and the othe...In South China four depositional sequences are recognized in the upper part of Upper Devonian and Tournaisian. They are named SQ0 SQ1, SQ2 and SQ3 in ascending order. SQ0 is Strunian (uppermost Devonian), and the other three Tournaisian in age. These four depositional sequences appear to correlate fairly well with the four sequence recognized in Europe, North America and other areas. This may suggest that these sequences are synchronous depos- its resulted from the eustatic changes. The present study on sequence stratigraphy, biostratigraphy and event stratigraphy indicates that in neritic facies areas of South China, the Devonian-Carboniferous boundary, matching the boundary between Siphonodella praesulcata zone and S. sulcata zone in pelagic facies areas, is not only higher than the top of the Cystophrentis zone, but also higher than the top of the Devonian-Carboniferous boundary event bed. In neritic facies areas, the Devonian-Carbonifrerous boundary is marked by the most distinct transgressive surface within the Cystophrentiseudouralina interval zone, i. e. at the base of the TST of the SQ1. This boundary coincides with the top surface of the event bed resulted from the eustatic fall, and approximately corresponds to the basal part of Rseudouralina assemblage zone.展开更多
Sequence stratigraphical analysis was applied to the Upper Carboniferous-Lower Permian sedimentary succession of the northeastern Ordos Basin, north China based on data acquired from ten entire logging curves and eigh...Sequence stratigraphical analysis was applied to the Upper Carboniferous-Lower Permian sedimentary succession of the northeastern Ordos Basin, north China based on data acquired from ten entire logging curves and eight outcrops. The facies framework of the lithostratigraphical unit, the Taiyuan Formation comprises seven facies in two facies associations, varying from fluvio-delta to shelf-barrier islands. The facies are presented within a chronostratigraphical framework, linked by systems tract, which in turn are limited by flooding surfaces and sequence boundaries. Six third-order depositional sequences are recognised, bounded by six type 2 unconformities. An upwards-shallowing epicontinental sea sedimentary model is created, which consists of a sandstone, coal seam and carbonate succession.展开更多
The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence strat...The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence stratigraphy. Based on an integrated study of sequence stratigraphy with outcrop data, wells and regional seismic profiles, the Qom Formation is interpreted as a carbonate succession deposited in a mid.Tertiary back-arc basin. There are two second-order sequences （designated as SS1 and SS2） and five third-order sequences （designated as S1-S5）. Five distinct systems tracts including transgressive, highstand, forced regressive, slope margin and Iowstand have been recognized. The relationship between the sequences and lithologic sub-units has been collated and defined （S1 to S5 individually corresponding to A-C1, C2--C4, D-E, the lower and upper portions of F）; a relative sea level change curve and the sequence stratigraphic framework have been established and described in detail. The coincidence of relative sea level change between that of the determined back-arc basin and the world indicates that the sedimentary cycles of the Qom Formation are mainly controlled by eustatic cycles. The variable combination of the systems tracts and special tectonic-depositional setting causally underpin multiple sequence stratigraphic framework styles seen in the carbonates of the back-arc basin revealing： （1） a continental margin basin that developed some form of barrier, characterized by the development of multiple cycles of carbonate-evaporites; （2） a flat carbonate ramp, which occurred on the southern shelf formed by the lack of clastic supply from nearby magmatic islands plus mixed siliciclastics and carbonates that occurred on the northern shelf due to a sufficient clastics supply from the land; and （3） a forced regressive stratigraphic stacking pattern that occured on the southern shelf and in basin lows due to the uplifting of the southern shelf. Thick and widespread aggradational framework limestone usually occurs in the initial sequences （S1 and S3） of the supersequence, which led to preferential oil reservoir deposition but a lack of source and cap rocks, whereas the retrogradational and progradational framework limestone usually occurs in the later sequences （S2 and S4-S5） of the supersequence, which results in two perfect sets of source, reservoir and cap rock assemblies, so that the limestone in sub-member C2-C4 and the F-Member can be predicted as important objects for oil exploration.展开更多
Depositional sequences may be distinguished into six ranks of units as giga-, mega-, meso-, ortho-, sub- and micro-sequence, and are interpreted to be formed during the eustatic cycles with time-intervals of 500-6000 ...Depositional sequences may be distinguished into six ranks of units as giga-, mega-, meso-, ortho-, sub- and micro-sequence, and are interpreted to be formed during the eustatic cycles with time-intervals of 500-6000 Ma, 60-120 Ma, 30-40 Ma, 2-5 Ma, 0.1-0.4 Ma and 0.02-0.04 Ma respectively. All of them are thought to be essentially related to cosmological cycles, except the megasequence which may be caused by the long-term geothermal cycles on cratons. We deem that the depositional sequences, though often influenced variably by local tectonics and other factors, are primarily global and periodic in nature. We also hold that as one of the planets within the Galaxy, the earth must have been affected in various ways by other asteroids, and that the depositional sequences are merely the responses of the hydrosphere to the cosmological cycles in sedimentation.展开更多
Biostratigraphical data indicate that in the neritic facies areas of South China, the Devonian -Carboniferous boundary (DCB), matching the boundary between conodont Siphonodella praesulcata zone and S. sulcata zone, s...Biostratigraphical data indicate that in the neritic facies areas of South China, the Devonian -Carboniferous boundary (DCB), matching the boundary between conodont Siphonodella praesulcata zone and S. sulcata zone, should be drawn between rugose coral Cystophrentis zone and Pseudouralina zone, i.e. the Cystophrentis\ Pseudouralina inter val-zone. The top of the sea level fall event bed near the DCB is lower than the boundary between S. praesulcata and S. sulcata zones, but higher than the top of the Cysto phrentis zone. Sequence stratigraphical study shows that the sea level fall event bed near the DCB constitutes the shelf margin system tract (SMST) of a depositional sequence (SQ1) in both neritic and pelagic facies areas. The top surfaces of SMST of SQ1 is slightly lower than the base of S. sulcata zone in the pelagic facies areas. In neritic facies areas of South China, therefore, the Devonian - Carboniferous boundary is marked by the most distinct transgressive surface within the Cystophrentis\ Pseudouralina interval-zone, i.e. the base of the TST of SQ1. This boundary coincides with the top surface of the event bed resulted from the eustatic fall, and approximately corresponds to the base of Pseudouralina assemblage zone.展开更多
The Upper Proterozoic glacigenous rocks in the southeastern margin of the Yangtze platform were accumulated in a glacially influenced marine environment with extension set- ting. Two type I depositional sequences have...The Upper Proterozoic glacigenous rocks in the southeastern margin of the Yangtze platform were accumulated in a glacially influenced marine environment with extension set- ting. Two type I depositional sequences have been identified in the glacioclastic sediments the their boundaries enhanced by both tectonism and the incision of glaciation. The lower sequence (SQ1), comprising Changan and Fulu formations (Guangxi Province), Jiangkou and Xiangmen formations(Hunan Province) and their equivalents, is bounded by erosional unconformities both at the base and on the top. The upper sequence (SQ2), composed mainly of Nantuo Formation and its equivalents, is confined by an erosional unconformity at the base and covered by an exposure surface of karstification on the top. The depositional systems tracts are difficult to be distinguished directly and mainly characterized by the variation in glacioclastic supplies. Two types of episodic parasequeuces can be identified in the glacigenous rocks and are related to the evolution of depositional systems tracts. Both the sequences and parasequences are caused by autocyclic mechanism. The present research shows that the Upper Proterozoic glacigenous deposits are of significance for the analysis of the tectonic evolution of the Late Precambrian basin in South China.展开更多
Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）...Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）, and deltaic sandstones of the lowstand systems tract（LST） and falling stage systems tract（FSST）.Detailed petrographic observations suggest that the diagenetic features and related evolution of these deposits cannot be simply characterized and demonstrated in the depth domain.However, the occurrence of diagenetic minerals systematically depends on the studied interval within the HST, TST, LST, and FSST; therefore, diagenesis in this region can be better constrained when studied in the context of the depositional environments and sequence stratigraphic framework.The eogenetic processes in such settings include：（1） microcrystalline siderite precipitated as concretions in almost all environments and systems tracts, which inhibited further mechanical compaction;（2） grain dissolution and kaolinitization occurred in shoreface HST sandstones and deltaic LST and FSST sandstones;（3） glaucony was locally observed, which did not clearly reflect the controls of facies or sequence stratigraphy; and（4） cementation by pyrite aggregates occurred in the shoreface HST sandstones and deltaic LST sandstones.The mesogenetic diagenesis includes：（1） partial conversion of kaolinite into dickite in deltaic LST sandstones, and minor chlorite cementation in deltaic FSST sandstones;（2） transformation of kaolinite into illite and quartz cementation in deltaic LST and FSST sandstones;（3） frequent precipitation of ankerite and ferroan calcite in shoreface TST sandstones and early HST sandstones, forming baffles and barriers for fluid flow, with common calcite in shoreface HST sandstones as a late diagenetic cement; and（4） formation of dawsonite in the deltaic LST and FSST sandstones, which is interpreted to be a product of the invasion of a CO2-rich fluid, and acts as a good indicator of CO2-bearing reservoirs.This study has thus constructed a reliable conceptual model to describe the spatial and temporal distribution of diagenetic alterations.The results may provide an entirely new conceptual framework and methodology for successful gas exploration in the continental margins of offshore China, thus allowing us to predict and unravel the distribution and quality evolution of clastic reservoirs at a more detailed and reliable scale.展开更多
Various orders of sequences were recognized in the Tarim Basin from unconformities. Three mega-sequence groups, six mega-sequences, sixteen super-sequences and forty-two sequences were determined from the Sinian to th...Various orders of sequences were recognized in the Tarim Basin from unconformities. Three mega-sequence groups, six mega-sequences, sixteen super-sequences and forty-two sequences were determined from the Sinian to the Quaternary. The mega-sequences and super-sequences were in accordance with the locally tectonic events occurring in both the north and the south margins of the Tarim plate. The global sea level changes only worked to control formations in the tectonically stable periods or in the low order sequences. The sequences had close relationship to the source rocks, reservoirs and cap rocks, and the tectonic events determined the migration, accumulation, and preservation of the hydrocarbon. The three mega-sequence group cycles, including the early cycle-the Sinian-middle Devonian, the middle cycle-the upper Devonian-Triassic, and the late cycle-the Jurassic-Quaternary, corresponded to three reservoir formation cycles. So, it can be concluded that the local tectonic events controlled both the sequences and the distribution of oil and gas in the Tarim Basin.展开更多
The Shan 2 Member, Shan 1 Member and He 8 Member of the Mid-Late Permian Shanxi and lower Xiashihezi formations, in the southeastern Ordos Basin, together comprise -150 m of deltaic deposits. This sequence records an ...The Shan 2 Member, Shan 1 Member and He 8 Member of the Mid-Late Permian Shanxi and lower Xiashihezi formations, in the southeastern Ordos Basin, together comprise -150 m of deltaic deposits. This sequence records an overall evolution from deep marine environment to shallow lake associated with braided river, braided river delta and meandering river delta. Core description, well log interpretation, and stable isotope analysis, including carbon, oxygen and strontium, were conducted to understand the sedimentary evolution of Shan 2 to He 8 Member. The Shanxi Formation, which consists of the Shan 2 and Shan 1 members, is characterized by a tidal-influenced meandering river delta environment and a higher j13C value and S7Sr/S6Sr ratio and a lower jlSo value. The He 8 Member, the basal part of the Xiashihezi Formation, is featured by a braided river to braided river delta system and a lower j13C value, S7Sr/S6Sr ratio, and a higher jlSo value. Four third-order depositional sequences separated by five sequence boundaries are determined. Coarsening upward sequences of the Shan 2 Member-He 8 Member indicate a general regression trend, which can be correlated to global sea-level fall occurring during the Roadian-Wuchiapingian, as also evidenced by previous published zircon U-Pb results. The coal-bearing sequence （Shanxi Formation） to non-coal-bearing sequence （He 8 Member）, as well as a decrease of 87Sr/86Sr, suggest a trend from humid to arid climates. A combined effect of sea-level drop and a small uplift at the end of Shanxi Formation are proposed.展开更多
A rich assemblage of planktonic foraminifera has been studied from an outcrop of the Gurpi Formation, the hydrocarbon source rock in the southwest Iran, Deh Dasht area（Kuh-e Siah anticline）. Based on the distributio...A rich assemblage of planktonic foraminifera has been studied from an outcrop of the Gurpi Formation, the hydrocarbon source rock in the southwest Iran, Deh Dasht area（Kuh-e Siah anticline）. Based on the distribution of the planktonic foraminifera, eight biozones have been recognized that included：Dicarinella concavata Interval Zone（Earliest Santonian）, Dicarinella asymetrica Total Range Zone（Santonian to Earliest Campanian）, Globotruncanita elevata Partial Range Zone（Early Campanian）, Globotruncana ventricosa Interval Zone（Middle to Late Campanian）, Radotruncana calcarata Total Range Zone（Late Campanian）, Globotruncanella havanensis Partial Range Zone（Late Campanian）, Globotruncana aegyptiaca Interval Zone（Late to latest Campanian）, Gansserina gansseri Interval Zone（Latest Campanian to Early Maastrichtian）. These biozones indicates that the Gurpi Formation deposited during the Early Santonian- Early Maastrichtian. These biozones are compared to the most standard biozones defined in Tethysian domain. Based on distribution of morphotype groups of planktonic foraminifera, planktonic to benthic ratio（P/B） and content of carbonate, nine third-order sequences are recognized.展开更多
Based on a synthetic geological study of drilling,well logging and seismic data,core observations and geochemical analysis,it is recognized that Triassic sedimentary facies in the Tahe area of Tarim Basin include brai...Based on a synthetic geological study of drilling,well logging and seismic data,core observations and geochemical analysis,it is recognized that Triassic sedimentary facies in the Tahe area of Tarim Basin include braided river deposits filling erosional valleys,and sublacustrine fan,canyon and delta facies.Braided river deposits filling erosional valleys are dominated by coarse-grained lithic quartz sandstone with oblique bedding,and represent the most important sedimentation type of sandstone in the study area.Sublacustrine fan and canyon facies are mainly distributed in the Middle Oil Member.Most delta sediments are deposited in highstand system tract(HST),Because of frequent changes in base level,delta sediments are commonly eroded and rarely preserved.Sedimentary cycles are clearly reflected by lithology,sedimentary structures and well logging data,and are closely related to the changes in lacustrine level.In accordance with the basic principle of sequence subdivision,seven type-I boundaries can be recognized in Triassic strata and six type-I sequences are subdivided correspondingly.In general,lowstand system tract(LST) is well developed within stratigraphic sequences and forms the main body of reservoir sandstone in this area;highstand system tract(HST) and transgressive system tract(TST) are often eroded by upper sequences or missed,Although various factors have different influences on terrestrial sequence stratigraphy,the classical sequence stratigraphy theory proposed by VAIL can be applied to terrestrial strata.展开更多
基金the National Natural Science Foundation of China(Grant Nos.42077410 and 41872112).We acknowledge the insights and efforts of journal editor(Jie Hao)and three anonymous reviewers that improved the quality of the manuscript.
文摘The study of sequence stratigraphy often focuses on shallow marine and shelf-edge regions,while research on deep-sea stratigraphic sequences remains relatively weak.This study,based on highresolution 3D seismic data and drilling information,utilized sequence stratigraphy and seismic sedimentology as guidelines,and employed seismic interpretation methods to performed a division of deepsea stratigraphic sequences within the Romney 3D seismic survey area in the deep-water Taranaki Basin,New Zealand.Furthermore,it analyzed the characteristics of typical depositional systems and their associated controlling factors.The findings are as follows:(1)Based on seismic reflection termination relationships and seismic facies characteristics,four second-order sequence boundaries and nine thirdorder sequence boundaries were identified,resulting in the delineation of three second-order sequences and twelve third-order sequences in the basin.(2)Five seismic facies were recognized,corresponding to five typical sedimentary bodies:mass transport deposits(MTDs),deep-water channel,levee deposits,deltaic deposits,and pelagic deposits.However,due to the relatively thin sedimentary thickness of carbonate sediments,the seismic facies characteristics of carbonate sediments cannot be discerned in seismic data,but can be identified based on well data.Deltaic sediments mainly developed during the rift stage of the basin,while carbonate sediments formed during the transition from a passive to an active margin.Deep-water channel and levee deposits and MTDs emerged during the active margin stage,while pelagic deposits are ubiquitous in marine environments.(3)The uplift of New Zealand's interior and climate-driven erosion caused the resurgence of clastic sediments,which began to be transported to the deep sea,the seafloor topography would directly affect the movement path of sediment gravity flow,and sediment supply can affect the development and evolution of sedimentary systems.(4)Event deposits boundaries,such as erosional scour surfaces formed by channels and unconformities created by MTDs,can serve as boundaries for the division of deep-water stratigraphic sequences.This study proposes a method for delineating deep-water stratigraphic sequences using event deposits,particularly suitable under conditions where the influence of relative sea-level changes on deep-water deposits is relatively weak.This research not only enhances the understanding of deep-water depositional sequences but also provides a reference for studies on the evolution of deep-water deposition and its controlling factors in research areas with similar geological backgrounds worldwide.
文摘In the Northern Himalayan region of Southern Xizang (Tibet),from the Lower Triassic to Upper Eocene 73 Sequences have been identified, with an average duration of 2.9 Ma;these can in turn be grouped into 24 super-Sequences and 6 super-sequence sets. During Mesozoic and Paleogene, several large sea - level falls occurred in the Eastern Neo-Tethys. Among the recognized sea- level falls, the important ones include those at the ages of 255 Ma, 215 Ma,177 Ma, 138 Ma, 103 Ma and 68 Ma .Those at 239 Ma, 215 Ma, 157 Ma,80 Ma, 50Ma and 36 Ma are also significant. The third-order Sequences and sea-level cycles Probably reflect mainly global sea - level fluctuations, while the higher rank cycles seem more closely related to the basin evolution of the Neo-Tethys. Based on the study, six major periods have been suggested for ths tectonic evolution of the Eastern Neo-Tethys and the plates, i. e. the Pangea Period (Pre-Triassic), continental rifting Period (Triassic to Early Jurassic ), inter-continental sea Period (Middle Jurassic ), continental divergence period (late Middle Jurassic to Early Cretaceous ), continental convergence period (Late Cretaceous ) and the continental collision Period (Paleogene ). These major Periods can be further subdivided into eight stages according to the basin evolution. In each of the periods and Stages, Sequences and their boundaries show clear characters related to the tectonic background. The study indicater that the initial breakup of the Pangea along the Indus- Yarlung may have taken Place around 239 Ma. The Late Bathonian to Early Callovian seems to have been a critical time in the evolution of the Neo-Tethys, with the turning Point around 158 Ma. The blocks split from the northern margin of the Gondwana continual did not obviously drift away from the Indian Plate until Callovian .The oceanic crust subduction in the Neo- Tethys may have Started at 113Ma, while the contraction of the ocean probably began at 107- 103 Ma. The initial contact of the Indian Plate with the Eurasian plate may have taken Place around 80 Ma, with strong uplifting and thrushng in Late Paleocene.
文摘This research uses both three-dimensional(3D)modeling and geologic well control to piece back together the architectural parts of the Late Cretaceous formations.The goal is to figure out the sizes,directions,locations,and controls of the layers of the fluvial sandstone reservoirs.Sequence stratigraphy is essential for 3D reservoir modeling and petroleum geology understanding in the Bahga oilfield.The purpose of this work is to create a static model that shows the layers and facies distribution in the reservoir interval.We will use data from nine well logs and 22 seismic lines calibrated by the Abu Roash G Member reservoir core intervals to accomplish this.The petrophysical study discovered three parts in the Abu Roash G Member reservoir rock:channel fill that is affected by tides,channel fill that is dominated by tides(intertidal sands),and channel top with lenticular bedded sandstone.The model's findings point to the existence of an NNW-oriented sand body,which could be a prime location to produce hydrocarbons.The original oil in place(OOIP)is about 3,438,279 Stock Tank Barrels(STB),and the oil reserve reaches up to 1,031,484(STB).Sequence stratigraphic analysis using seismic and well log information(SB)reveals that the Upper Cretaceous AR/G reservoir of the Bahga field is characterized by third-and fourth-order stratigraphic sequences,which are constrained by three Maximum Flooding Surfaces(MFS)and two Sequence Boundaries.The integration of the derived geological model and sequence stratigraphic results can lower future extraction risk by identifying the locations and trends of the geologic facies with the necessary petrophysical properties for the hydrocarbon accumulations.
文摘A Oilfield is the most representative mid to deep oil field in the Bohai Sea, with the main oil bearing intervals being the upper and middle Shahejie-3 sections of the Paleogene Shahejie Formation. By combining well seismic analysis, the middle section of Shahejie-3 is divided into high-level system tract and forced lake retreat system tract, corresponding to the II oil formation and I oil formation, respectively. Using sequence stratigraphy methods, based on seismic profiles and drilling lithological cycles, the high stand system tract is divided into 5 stages of delta progradation. The first and second stages are high angle S-type progradation with large sedimentary thickness, the third stage is oblique progradation, and the fourth and fifth stages are S-oblique composite progradation;By combining seismic data, we characterized the large-scale (8 small-scale) progradation bodies of 5 periods, clarified the distribution characteristics of reservoir planes, and laid the foundation for the later exploration of oilfield potential.
基金financially supported by the Key R&D Program of Guangxi Zhuang Autonomous Region(2021AB30011)。
文摘Silicalites are extensively developed in the Liujiang Formation(Fm.)of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales.This stratigraphic combination represents a special sequence stratigraphy formed in special deep-water environments,which not only gives the shales unusual spatio-temporal distribution features,but also induces the shales in the Liujiang Fm.to frequently be rich in organic matter(OM).This study summarises the special deep-water sedimentary succession of the Liujiang Fm.,which is mainly distributed around synsedimentary faults,as well as establishing the sequence stratigraphic frameworks of the Liujiang Fm.in the west-east and southwest-northeast directions.Under the sequence stratigraphic frameworks,the spatio-temporal distribution features of the organic-rich shales of the Liujiang Fm.and the regional variations of the Liujiang Fm.were investigated.In addition,the rock components and OM occurrence states of the organic-rich shales were also observed and described in detail under the microscope.The results show that the organic-rich shales were formed temporally primarily during the third-order sea-level falling stage,developed spatially mainly on the east and west sides of the study area,as well as that the OM accumulation is closely related to tentaculitoids and seems to be influenced by a'biological pump'.
基金This research was supported by the Project for the Survey of Land and Resources in China(1212010633901)National Natural Science Foundation of China(Grant No.41572090)。
文摘There are 9 major coal-accumulating periods during geological history in China,including the Early Carboniferous,Late Carboniferous-Early Permian,Middle Permian,Late Permian,Late Triassic,Early-Middle Jurassic,Early Cretaceous,Paleogene and Neogene.The coal formed in these periods were developed in different coal-accumulating areas(CAA)including the North China,South China,Northwest China,Northeast China,the Qinghai–Tibet area,and China offshore area.In this paper,we investigated depositional environments,sequence stratigraphy,lithofacies paleogeography and coal accumulation pattern of five major coal-accumulating periods including the Late Carboniferous to Middle Permian of the North China CAA,the Late Permian of the South China CAA,the Late Triassic of the South China CAA,the Early-Middle Jurassic of the North and Northwest China CAA,and the Early Cretaceous in the Northeast China CAA.According to distribution of the coal-bearing strata and the regional tectonic outlines,we have identified distribution range of the coal-forming basins,sedimentary facies types and coal-accumulating models.The sequence stratigraphic frameworks of the major coal-accumulating periods were established based on recognition of a variety of sequence boundaries.The distribution of thick coals and migration patterns of the coal-accumulating centers in the sequence stratigraphic framework were analyzed.The lithofacies paleogeography maps based on third-order sequences were reconstructed and the distribution of coal accumulation centers and coal-rich belts were predicted.
文摘Three third-order sequences and about one hundred high-frequency cycles or Milankovitchcycles within the Late Permian Changxingian to Early Triassic Griesbachian are identified in theMeishan Section of Changxing, Zhejiang Province, southern China, the candidate stratotype sec-tion of the global Permo-Triassic boundary, based on a detailed study of the biological,ecological and high-resolution allochthonous cyclic events, microfacies and depositional systems.Furthermore, the stacking pattern of the depositional systems across various Changxingian andGriesbachian sedimentary facies of the Lower Yangtze and the sequence stratigraphic frameworkare outlined with the Meishan section as the principal section. In this paper the habitat types offossil biota are applied to semiquantitative palaeobathymetry and the study of relative sea levelchanges.
基金supported by the China National Key Research Project(No.2011ZX05009-002)the MOE Yangtze River Scholar and Innovative Team Program of China(No.IRT0864)
文摘The Lower Permian Shanxi （山西） Formation is one of the main gas-bearing stratio graphic units in northeastern Ordos （鄂尔多斯） Basin, China. Based on an integrated investigation of well logs, cores, and outcrop, we delineated the sedimentary facies of the lower member of the Shanxi Formation and divided the succession into three third-order sequences from base to top as SQ1, SQ2, and SQ3. The lower region of Shanxi Formation was deposited in the following sedimentary facies or subfacies： subaqueous braided channel, subaqueous interdistributary, mouth bar, swamp and shelf in the Daniudi （~z~=J~） Gas Field and braided channel, and shelf and lake at Heidaigon （~J） outcrop. Braided-river deposits form the lowstand systems tract （LST） in each sequence. Braided channels mark the sequence boundaries at Heidaigou outcrop. A shelf and lake depositional environment with dark gray mudstone forms the transgressive systems tract （TST）. The location where dark gray mudstone first appears above the braided channel marks the first flooding surface （FFS）, and the end of that marks the maximum flooding surface （MFS）. The highstand systems tract （HST） deposits are fine-grained sediments with an aggradational parasequence at Heidaigou outcrop and swamp coalbed in the Daniudi Gas Field. Mouth-bar sand bodies in braided delta front, which form the LST in each sequence, form excellent reservoirs in the Daniudi Gas Field.
基金This study was supported by the Ministry of Sciences and Technology of China(2001CB209100),
文摘The Lower Cretaceous strata in the Kuqa Basin in Xinjiang are marked by a set of arid red beds. Several types of sedimentary fades can be identified in this set of arid red beds: mudstones of the plaza and intracontinental sebkha, aeolian sandstones, sandy conglomerates of the intermittent river, conglomerates of the pluvial fan, etc. These types of sedimentary facies constitute a typical desert system. Therefore, the Cretaceous strata in the Kuqa Basin provide a favorable condition for studies of sequence stratigraphic divisions of the desert system. With the rise and fall of the base level of the sedimentary basin, cyclicity is clearly revealed in stratigraphic records, which helps the identification of the third-order sequences. Based on the cyclicity in stratigraphic records, 5 third-order sequences can be found in the strata of the Early Cretaceous in the Kuqa Basin. These sequences comprise a second-order tectonic sequence. The primary feature of these third-order sequences is of an upward-fining sedimentary succession formed by a succession of 'coarse sediments of the alluvial system-fine sediments of the lake system'. The result of this study shows that aeolian sandstones are the best reservoirs of natural gas in the Cretaceous strata in the Kuqa Basin, and that the Kela-2 gas field is the first large gas field dominated by aeolian sandstone reservoirs in China.
文摘In South China four depositional sequences are recognized in the upper part of Upper Devonian and Tournaisian. They are named SQ0 SQ1, SQ2 and SQ3 in ascending order. SQ0 is Strunian (uppermost Devonian), and the other three Tournaisian in age. These four depositional sequences appear to correlate fairly well with the four sequence recognized in Europe, North America and other areas. This may suggest that these sequences are synchronous depos- its resulted from the eustatic changes. The present study on sequence stratigraphy, biostratigraphy and event stratigraphy indicates that in neritic facies areas of South China, the Devonian-Carboniferous boundary, matching the boundary between Siphonodella praesulcata zone and S. sulcata zone in pelagic facies areas, is not only higher than the top of the Cystophrentis zone, but also higher than the top of the Devonian-Carboniferous boundary event bed. In neritic facies areas, the Devonian-Carbonifrerous boundary is marked by the most distinct transgressive surface within the Cystophrentiseudouralina interval zone, i. e. at the base of the TST of the SQ1. This boundary coincides with the top surface of the event bed resulted from the eustatic fall, and approximately corresponds to the basal part of Rseudouralina assemblage zone.
基金supported by the National Major Fundamental Research and Development Project of China(Grant No.2003CB214600)the State Key Program of National Natural Science of China(Grant No. 90814005)
文摘Sequence stratigraphical analysis was applied to the Upper Carboniferous-Lower Permian sedimentary succession of the northeastern Ordos Basin, north China based on data acquired from ten entire logging curves and eight outcrops. The facies framework of the lithostratigraphical unit, the Taiyuan Formation comprises seven facies in two facies associations, varying from fluvio-delta to shelf-barrier islands. The facies are presented within a chronostratigraphical framework, linked by systems tract, which in turn are limited by flooding surfaces and sequence boundaries. Six third-order depositional sequences are recognised, bounded by six type 2 unconformities. An upwards-shallowing epicontinental sea sedimentary model is created, which consists of a sandstone, coal seam and carbonate succession.
文摘The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence stratigraphy. Based on an integrated study of sequence stratigraphy with outcrop data, wells and regional seismic profiles, the Qom Formation is interpreted as a carbonate succession deposited in a mid.Tertiary back-arc basin. There are two second-order sequences （designated as SS1 and SS2） and five third-order sequences （designated as S1-S5）. Five distinct systems tracts including transgressive, highstand, forced regressive, slope margin and Iowstand have been recognized. The relationship between the sequences and lithologic sub-units has been collated and defined （S1 to S5 individually corresponding to A-C1, C2--C4, D-E, the lower and upper portions of F）; a relative sea level change curve and the sequence stratigraphic framework have been established and described in detail. The coincidence of relative sea level change between that of the determined back-arc basin and the world indicates that the sedimentary cycles of the Qom Formation are mainly controlled by eustatic cycles. The variable combination of the systems tracts and special tectonic-depositional setting causally underpin multiple sequence stratigraphic framework styles seen in the carbonates of the back-arc basin revealing： （1） a continental margin basin that developed some form of barrier, characterized by the development of multiple cycles of carbonate-evaporites; （2） a flat carbonate ramp, which occurred on the southern shelf formed by the lack of clastic supply from nearby magmatic islands plus mixed siliciclastics and carbonates that occurred on the northern shelf due to a sufficient clastics supply from the land; and （3） a forced regressive stratigraphic stacking pattern that occured on the southern shelf and in basin lows due to the uplifting of the southern shelf. Thick and widespread aggradational framework limestone usually occurs in the initial sequences （S1 and S3） of the supersequence, which led to preferential oil reservoir deposition but a lack of source and cap rocks, whereas the retrogradational and progradational framework limestone usually occurs in the later sequences （S2 and S4-S5） of the supersequence, which results in two perfect sets of source, reservoir and cap rock assemblies, so that the limestone in sub-member C2-C4 and the F-Member can be predicted as important objects for oil exploration.
基金This paper is an outcome of the research programof sequence stratigraphy (SSLC) supported by the Stateac~sinn of ScienCe and
文摘Depositional sequences may be distinguished into six ranks of units as giga-, mega-, meso-, ortho-, sub- and micro-sequence, and are interpreted to be formed during the eustatic cycles with time-intervals of 500-6000 Ma, 60-120 Ma, 30-40 Ma, 2-5 Ma, 0.1-0.4 Ma and 0.02-0.04 Ma respectively. All of them are thought to be essentially related to cosmological cycles, except the megasequence which may be caused by the long-term geothermal cycles on cratons. We deem that the depositional sequences, though often influenced variably by local tectonics and other factors, are primarily global and periodic in nature. We also hold that as one of the planets within the Galaxy, the earth must have been affected in various ways by other asteroids, and that the depositional sequences are merely the responses of the hydrosphere to the cosmological cycles in sedimentation.
基金The research is sponsored by the "SSLC", a state key project supported by the State Science and Technology Committee of China and the Ministry of Geology and Mineral Resources
文摘Biostratigraphical data indicate that in the neritic facies areas of South China, the Devonian -Carboniferous boundary (DCB), matching the boundary between conodont Siphonodella praesulcata zone and S. sulcata zone, should be drawn between rugose coral Cystophrentis zone and Pseudouralina zone, i.e. the Cystophrentis\ Pseudouralina inter val-zone. The top of the sea level fall event bed near the DCB is lower than the boundary between S. praesulcata and S. sulcata zones, but higher than the top of the Cysto phrentis zone. Sequence stratigraphical study shows that the sea level fall event bed near the DCB constitutes the shelf margin system tract (SMST) of a depositional sequence (SQ1) in both neritic and pelagic facies areas. The top surfaces of SMST of SQ1 is slightly lower than the base of S. sulcata zone in the pelagic facies areas. In neritic facies areas of South China, therefore, the Devonian - Carboniferous boundary is marked by the most distinct transgressive surface within the Cystophrentis\ Pseudouralina interval-zone, i.e. the base of the TST of SQ1. This boundary coincides with the top surface of the event bed resulted from the eustatic fall, and approximately corresponds to the base of Pseudouralina assemblage zone.
文摘The Upper Proterozoic glacigenous rocks in the southeastern margin of the Yangtze platform were accumulated in a glacially influenced marine environment with extension set- ting. Two type I depositional sequences have been identified in the glacioclastic sediments the their boundaries enhanced by both tectonism and the incision of glaciation. The lower sequence (SQ1), comprising Changan and Fulu formations (Guangxi Province), Jiangkou and Xiangmen formations(Hunan Province) and their equivalents, is bounded by erosional unconformities both at the base and on the top. The upper sequence (SQ2), composed mainly of Nantuo Formation and its equivalents, is confined by an erosional unconformity at the base and covered by an exposure surface of karstification on the top. The depositional systems tracts are difficult to be distinguished directly and mainly characterized by the variation in glacioclastic supplies. Two types of episodic parasequeuces can be identified in the glacigenous rocks and are related to the evolution of depositional systems tracts. Both the sequences and parasequences are caused by autocyclic mechanism. The present research shows that the Upper Proterozoic glacigenous deposits are of significance for the analysis of the tectonic evolution of the Late Precambrian basin in South China.
基金Financial support was provided by the National Science and Technology Major Project of China (No.2011ZX05023-002-003)
文摘Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）, and deltaic sandstones of the lowstand systems tract（LST） and falling stage systems tract（FSST）.Detailed petrographic observations suggest that the diagenetic features and related evolution of these deposits cannot be simply characterized and demonstrated in the depth domain.However, the occurrence of diagenetic minerals systematically depends on the studied interval within the HST, TST, LST, and FSST; therefore, diagenesis in this region can be better constrained when studied in the context of the depositional environments and sequence stratigraphic framework.The eogenetic processes in such settings include：（1） microcrystalline siderite precipitated as concretions in almost all environments and systems tracts, which inhibited further mechanical compaction;（2） grain dissolution and kaolinitization occurred in shoreface HST sandstones and deltaic LST and FSST sandstones;（3） glaucony was locally observed, which did not clearly reflect the controls of facies or sequence stratigraphy; and（4） cementation by pyrite aggregates occurred in the shoreface HST sandstones and deltaic LST sandstones.The mesogenetic diagenesis includes：（1） partial conversion of kaolinite into dickite in deltaic LST sandstones, and minor chlorite cementation in deltaic FSST sandstones;（2） transformation of kaolinite into illite and quartz cementation in deltaic LST and FSST sandstones;（3） frequent precipitation of ankerite and ferroan calcite in shoreface TST sandstones and early HST sandstones, forming baffles and barriers for fluid flow, with common calcite in shoreface HST sandstones as a late diagenetic cement; and（4） formation of dawsonite in the deltaic LST and FSST sandstones, which is interpreted to be a product of the invasion of a CO2-rich fluid, and acts as a good indicator of CO2-bearing reservoirs.This study has thus constructed a reliable conceptual model to describe the spatial and temporal distribution of diagenetic alterations.The results may provide an entirely new conceptual framework and methodology for successful gas exploration in the continental margins of offshore China, thus allowing us to predict and unravel the distribution and quality evolution of clastic reservoirs at a more detailed and reliable scale.
文摘Various orders of sequences were recognized in the Tarim Basin from unconformities. Three mega-sequence groups, six mega-sequences, sixteen super-sequences and forty-two sequences were determined from the Sinian to the Quaternary. The mega-sequences and super-sequences were in accordance with the locally tectonic events occurring in both the north and the south margins of the Tarim plate. The global sea level changes only worked to control formations in the tectonically stable periods or in the low order sequences. The sequences had close relationship to the source rocks, reservoirs and cap rocks, and the tectonic events determined the migration, accumulation, and preservation of the hydrocarbon. The three mega-sequence group cycles, including the early cycle-the Sinian-middle Devonian, the middle cycle-the upper Devonian-Triassic, and the late cycle-the Jurassic-Quaternary, corresponded to three reservoir formation cycles. So, it can be concluded that the local tectonic events controlled both the sequences and the distribution of oil and gas in the Tarim Basin.
基金supported by the National Natural Science Foundation of China(Grant No.41706063)the Basic Scientific Fund for National Public Research Institute of China(Grant No.2017Q08)the China Postdoctoral Science Foundation(Grant No.2016M602087)
文摘The Shan 2 Member, Shan 1 Member and He 8 Member of the Mid-Late Permian Shanxi and lower Xiashihezi formations, in the southeastern Ordos Basin, together comprise -150 m of deltaic deposits. This sequence records an overall evolution from deep marine environment to shallow lake associated with braided river, braided river delta and meandering river delta. Core description, well log interpretation, and stable isotope analysis, including carbon, oxygen and strontium, were conducted to understand the sedimentary evolution of Shan 2 to He 8 Member. The Shanxi Formation, which consists of the Shan 2 and Shan 1 members, is characterized by a tidal-influenced meandering river delta environment and a higher j13C value and S7Sr/S6Sr ratio and a lower jlSo value. The He 8 Member, the basal part of the Xiashihezi Formation, is featured by a braided river to braided river delta system and a lower j13C value, S7Sr/S6Sr ratio, and a higher jlSo value. Four third-order depositional sequences separated by five sequence boundaries are determined. Coarsening upward sequences of the Shan 2 Member-He 8 Member indicate a general regression trend, which can be correlated to global sea-level fall occurring during the Roadian-Wuchiapingian, as also evidenced by previous published zircon U-Pb results. The coal-bearing sequence （Shanxi Formation） to non-coal-bearing sequence （He 8 Member）, as well as a decrease of 87Sr/86Sr, suggest a trend from humid to arid climates. A combined effect of sea-level drop and a small uplift at the end of Shanxi Formation are proposed.
基金the University of Isfahan for providing financial support
文摘A rich assemblage of planktonic foraminifera has been studied from an outcrop of the Gurpi Formation, the hydrocarbon source rock in the southwest Iran, Deh Dasht area（Kuh-e Siah anticline）. Based on the distribution of the planktonic foraminifera, eight biozones have been recognized that included：Dicarinella concavata Interval Zone（Earliest Santonian）, Dicarinella asymetrica Total Range Zone（Santonian to Earliest Campanian）, Globotruncanita elevata Partial Range Zone（Early Campanian）, Globotruncana ventricosa Interval Zone（Middle to Late Campanian）, Radotruncana calcarata Total Range Zone（Late Campanian）, Globotruncanella havanensis Partial Range Zone（Late Campanian）, Globotruncana aegyptiaca Interval Zone（Late to latest Campanian）, Gansserina gansseri Interval Zone（Latest Campanian to Early Maastrichtian）. These biozones indicates that the Gurpi Formation deposited during the Early Santonian- Early Maastrichtian. These biozones are compared to the most standard biozones defined in Tethysian domain. Based on distribution of morphotype groups of planktonic foraminifera, planktonic to benthic ratio（P/B） and content of carbonate, nine third-order sequences are recognized.
基金Project(2008ZX05002-005) supported by the State Major Special Science and Technology Foundation of China
文摘Based on a synthetic geological study of drilling,well logging and seismic data,core observations and geochemical analysis,it is recognized that Triassic sedimentary facies in the Tahe area of Tarim Basin include braided river deposits filling erosional valleys,and sublacustrine fan,canyon and delta facies.Braided river deposits filling erosional valleys are dominated by coarse-grained lithic quartz sandstone with oblique bedding,and represent the most important sedimentation type of sandstone in the study area.Sublacustrine fan and canyon facies are mainly distributed in the Middle Oil Member.Most delta sediments are deposited in highstand system tract(HST),Because of frequent changes in base level,delta sediments are commonly eroded and rarely preserved.Sedimentary cycles are clearly reflected by lithology,sedimentary structures and well logging data,and are closely related to the changes in lacustrine level.In accordance with the basic principle of sequence subdivision,seven type-I boundaries can be recognized in Triassic strata and six type-I sequences are subdivided correspondingly.In general,lowstand system tract(LST) is well developed within stratigraphic sequences and forms the main body of reservoir sandstone in this area;highstand system tract(HST) and transgressive system tract(TST) are often eroded by upper sequences or missed,Although various factors have different influences on terrestrial sequence stratigraphy,the classical sequence stratigraphy theory proposed by VAIL can be applied to terrestrial strata.
