Seven third-order transgressive-regressive sequences are recognized in the Early Triassic -Early Carnian stratigraghc succession of Guizhou-Guangxi region, South China. Based on currently available ages by the correla...Seven third-order transgressive-regressive sequences are recognized in the Early Triassic -Early Carnian stratigraghc succession of Guizhou-Guangxi region, South China. Based on currently available ages by the correlation of conodont ammonites and bivalve faunas, these sequences range approximately from 1.0 Ma to 5.6 Ma, with the average of 3 Ma. They occur largely in the Griesbachian-Dienerian, Smithian,uppermost Smithian-lowermost Anisian, Lower Anisian, Middle Anisian, Upper Anisian-Upper Ladinian and the uppermost Ladinian-Lower Carnian respectively, and can be grouped into three second-order transgressive-regressive supersequences. A relative sea level curve is established from the sequence stratigraghic analysis. Transgressive-regressive sequences,bounded by transgressive surfaces and the correlatable unconformities, are real unconformity-bounded units of lower rank. Each sequence comprises transgressive, highstand and regressive systems tracts, and can be easily correlated with the depositional sequence.展开更多
The reservoirs within the Chang 8 Member of Yanchang （延长） Formation in the south- western Ordos basin are characterized by low permeability. It is significant to build a high-resolution sequence stratigraphic fram...The reservoirs within the Chang 8 Member of Yanchang （延长） Formation in the south- western Ordos basin are characterized by low permeability. It is significant to build a high-resolution sequence stratigraphic framework for the exploration and development of these reservoirs. Based on an integrated investigation of well logs, seismic data, cores and outcrops, the Chang 8 Member is interpreted as a 3rd-order transgressive-regressive （T-R） sequence, which consists of six 4th-order T-R se- quences, namely, K1, K2, K3, K4, K5 and K6, respectively, from base to top. Each 4th-order sequence comprises a transgressive systems tract overlain by a regressive systems tract. From K1 to transgressive systems tract of K4, it is characterized by the landward shifts of facies and overall retrogradational sequence stacking pattern due to accommodation increase more than sediment supply during the 3rd-order base-level rise. The distributary channels are mainly deposited in the transgressive systems tracts, and the interdistributary bays, sheet sands, and small-scale mouth bars are primarily developed in the regressive systems tracts in response to the 4th-order base-level fluctuations. From the regressivesystems tracts of K4 to K6, it is characterized by the basinward shifts of facies and overall progradational sequence stacking pattern because of accommodation increase less than sediment sup- ply during a fall in 3rd-order base level. The distributary channels are mainly accumulated in the transgressive systems tracts, and distributary channels and mouth bars are deposited in the regressive systems tracts as a result of the 4th-order base-level changes. Detailed stratigraphic and sedimentoiogical analyses indicate that sequences K1, K2, K5 and K6, as well as the basin edge of K3 and K4, remain potential for exploration and development due to their high reservoir quality in response to the low accommodation and more sediment supply.展开更多
The Chhasra Formation(CF)of Kutch Basin exemplifies a typical mixed siliciclastic-carbonate system with alternations of biostromal carbonate and fine-grained siliciclastic beds.The CF is subdivided into two members:th...The Chhasra Formation(CF)of Kutch Basin exemplifies a typical mixed siliciclastic-carbonate system with alternations of biostromal carbonate and fine-grained siliciclastic beds.The CF is subdivided into two members:the lower Claystone(CM)and the upper Siltstone(SM)member.Three CM outcrops(P1-P3)comprising buried palaeosols that formed under a specific environmental set-up involving imperfectly to poorly drained conditions,are exposed along the Berwali River.The biostromal carbonate beds,alternating with the palaeosols,contain invertebrate bioclasts(bivalves,gastropods,echinoids,etc.)and are characterized by a paucispecific firmground Thalassinoides ichnofabric.At section P1,below the contact between the underlying palaeosol and overlying carbonate,Thalassinoides transforms into firmground Gyrolithes inside the palaeosol forming a compound ichnotaxon.The palaeosol intervals of sections P1 and P2 consist of a Vondrichnus-Termitichnus-root trace ichnofabric defining the Termitichnus ichnofacies.At section P3,lenses of fully bioturbated siltstones with a monospecific firmground Thalassinoides ichnofabric can be observed within an overall silty palaeosol horizon,thereby,locally cross-cutting the pedogenic features.The ichnofabrics of section P3 indicate polyphase pedogenesis with three stages:(1)initial stage:pedogenesis in siltstone of undefined depositional affinity which was obscured by pedogenic processes,(2)transient stage:recurring marine incursions and colonization by crustaceans within the lens-shaped palaeotopographic depressions overprinting the palaeosol,and(3)final stage:subaerial exposure and another preserved phase of pedogenesis.The CM shows an apparent low-order T-R(transgressive-regressive)cyclicity within a 3rd-order TST(transgressive systems tract)that is supported by pedogenic intensity,ichnofabrics,and reciprocal sedimentation near the Miocene basin margin,though the cyclicity can be the result of both autogenic and/or lowerorder allogenic changes.展开更多
The Nenjiang Formation in the Songliao Basin is a symmetrical sequence of progradation-retrogradation,and is formed in the transgression cycle and regression cycle(T-R cycles)of the base level of deposition.We analyze...The Nenjiang Formation in the Songliao Basin is a symmetrical sequence of progradation-retrogradation,and is formed in the transgression cycle and regression cycle(T-R cycles)of the base level of deposition.We analyzed the drilling,well logging,core data,and seismic profiles of basin level,and by using the sequence stratigraphy,identified one secondary sequence boundary,two third-order sequence boundaries,and eight fourth-order sequence boundaries in the Nenjiang Formation.These eleven sequence boundaries can be divided into structural unconformity,depositional unconformity,flooding surface,and forced regression surface.Therefore the Nenjiang Formation can be subdivided into one secondary sequence,three third-order sequences,and ten fourth-order sequences.We have restored the sedimentary filling evolution within the stratigraphic framework of fourth-order sequences in the Nenjiang Formation.The sedimentary period of the first member of the Nenjiang Formation was corresponded to the global transgression period,which is also the development period of transgression cycle(T cycle),when the lake basin had the largest scope and deepest sedimentary water,the SB07(the maximum flooding surface)was formed on the top of strata during this period;covering above the SB07,there developed a set of condensation layer-oil shale,which is distributed in the whole basin and is the important source bed and regional cover.Therefore,a retrogradation sequence was formed in the T cycle of the first member of the Nenjiang Formation,characterized by the retrograding delta at a low angle.The delta has a giant front,a small plain,and many underwater distributary channels.Meanwhile,large gravity flow channels and sublacustrine fans are developed in the front of the delta.During the depositional period of the second member of the Nenjiang Formation,the R cycle began to develop due to the compression of the pacific tectonic domain;the source direction rotated 90°along with the eastern uplifting of the basin,and formed a series of east-west prograded and forced retrogradations.The prograding delta at high angel was developed in the interior of the sequence;the delta had a small front,a giant plain,and fewer underwater distributary channels,with the collapse at the foreslope,forming a series of slump fans.The slump fans can be divided into three types:discrete type,superimposed type,and fluid type.We built a whole"triad model"of the slump fan.Pointed out that the sequence of forced retrogradation formed by R cycle is a good structural mark of basin optimization,and rejected the viewpoint of"transgression"in the Nenjiang Formation of the Songliao Basin.展开更多
文摘Seven third-order transgressive-regressive sequences are recognized in the Early Triassic -Early Carnian stratigraghc succession of Guizhou-Guangxi region, South China. Based on currently available ages by the correlation of conodont ammonites and bivalve faunas, these sequences range approximately from 1.0 Ma to 5.6 Ma, with the average of 3 Ma. They occur largely in the Griesbachian-Dienerian, Smithian,uppermost Smithian-lowermost Anisian, Lower Anisian, Middle Anisian, Upper Anisian-Upper Ladinian and the uppermost Ladinian-Lower Carnian respectively, and can be grouped into three second-order transgressive-regressive supersequences. A relative sea level curve is established from the sequence stratigraghic analysis. Transgressive-regressive sequences,bounded by transgressive surfaces and the correlatable unconformities, are real unconformity-bounded units of lower rank. Each sequence comprises transgressive, highstand and regressive systems tracts, and can be easily correlated with the depositional sequence.
基金supported by the National Natural Science Foundation of China (No. 40702024)
文摘The reservoirs within the Chang 8 Member of Yanchang （延长） Formation in the south- western Ordos basin are characterized by low permeability. It is significant to build a high-resolution sequence stratigraphic framework for the exploration and development of these reservoirs. Based on an integrated investigation of well logs, seismic data, cores and outcrops, the Chang 8 Member is interpreted as a 3rd-order transgressive-regressive （T-R） sequence, which consists of six 4th-order T-R se- quences, namely, K1, K2, K3, K4, K5 and K6, respectively, from base to top. Each 4th-order sequence comprises a transgressive systems tract overlain by a regressive systems tract. From K1 to transgressive systems tract of K4, it is characterized by the landward shifts of facies and overall retrogradational sequence stacking pattern due to accommodation increase more than sediment supply during the 3rd-order base-level rise. The distributary channels are mainly deposited in the transgressive systems tracts, and the interdistributary bays, sheet sands, and small-scale mouth bars are primarily developed in the regressive systems tracts in response to the 4th-order base-level fluctuations. From the regressivesystems tracts of K4 to K6, it is characterized by the basinward shifts of facies and overall progradational sequence stacking pattern because of accommodation increase less than sediment sup- ply during a fall in 3rd-order base level. The distributary channels are mainly accumulated in the transgressive systems tracts, and distributary channels and mouth bars are deposited in the regressive systems tracts as a result of the 4th-order base-level changes. Detailed stratigraphic and sedimentoiogical analyses indicate that sequences K1, K2, K5 and K6, as well as the basin edge of K3 and K4, remain potential for exploration and development due to their high reservoir quality in response to the low accommodation and more sediment supply.
基金the following funding agencies for the research grants:Science and Engineering Research Board (SERB)Government ofIndia (grant#CRG/2018/000259 to SDG)+2 种基金Industrial Research and Consultancy Centre (IRCC)IIT Bombay (seed grant#RD/0517-IRCCSH0-035 to SDG)Council of Scientific&Industrial Research (CSIR) (doctoral scholarship for AS)。
文摘The Chhasra Formation(CF)of Kutch Basin exemplifies a typical mixed siliciclastic-carbonate system with alternations of biostromal carbonate and fine-grained siliciclastic beds.The CF is subdivided into two members:the lower Claystone(CM)and the upper Siltstone(SM)member.Three CM outcrops(P1-P3)comprising buried palaeosols that formed under a specific environmental set-up involving imperfectly to poorly drained conditions,are exposed along the Berwali River.The biostromal carbonate beds,alternating with the palaeosols,contain invertebrate bioclasts(bivalves,gastropods,echinoids,etc.)and are characterized by a paucispecific firmground Thalassinoides ichnofabric.At section P1,below the contact between the underlying palaeosol and overlying carbonate,Thalassinoides transforms into firmground Gyrolithes inside the palaeosol forming a compound ichnotaxon.The palaeosol intervals of sections P1 and P2 consist of a Vondrichnus-Termitichnus-root trace ichnofabric defining the Termitichnus ichnofacies.At section P3,lenses of fully bioturbated siltstones with a monospecific firmground Thalassinoides ichnofabric can be observed within an overall silty palaeosol horizon,thereby,locally cross-cutting the pedogenic features.The ichnofabrics of section P3 indicate polyphase pedogenesis with three stages:(1)initial stage:pedogenesis in siltstone of undefined depositional affinity which was obscured by pedogenic processes,(2)transient stage:recurring marine incursions and colonization by crustaceans within the lens-shaped palaeotopographic depressions overprinting the palaeosol,and(3)final stage:subaerial exposure and another preserved phase of pedogenesis.The CM shows an apparent low-order T-R(transgressive-regressive)cyclicity within a 3rd-order TST(transgressive systems tract)that is supported by pedogenic intensity,ichnofabrics,and reciprocal sedimentation near the Miocene basin margin,though the cyclicity can be the result of both autogenic and/or lowerorder allogenic changes.
基金supported by National Basic Research Program of China(Grant Nos.2006CB701404,2009CB219308)
文摘The Nenjiang Formation in the Songliao Basin is a symmetrical sequence of progradation-retrogradation,and is formed in the transgression cycle and regression cycle(T-R cycles)of the base level of deposition.We analyzed the drilling,well logging,core data,and seismic profiles of basin level,and by using the sequence stratigraphy,identified one secondary sequence boundary,two third-order sequence boundaries,and eight fourth-order sequence boundaries in the Nenjiang Formation.These eleven sequence boundaries can be divided into structural unconformity,depositional unconformity,flooding surface,and forced regression surface.Therefore the Nenjiang Formation can be subdivided into one secondary sequence,three third-order sequences,and ten fourth-order sequences.We have restored the sedimentary filling evolution within the stratigraphic framework of fourth-order sequences in the Nenjiang Formation.The sedimentary period of the first member of the Nenjiang Formation was corresponded to the global transgression period,which is also the development period of transgression cycle(T cycle),when the lake basin had the largest scope and deepest sedimentary water,the SB07(the maximum flooding surface)was formed on the top of strata during this period;covering above the SB07,there developed a set of condensation layer-oil shale,which is distributed in the whole basin and is the important source bed and regional cover.Therefore,a retrogradation sequence was formed in the T cycle of the first member of the Nenjiang Formation,characterized by the retrograding delta at a low angle.The delta has a giant front,a small plain,and many underwater distributary channels.Meanwhile,large gravity flow channels and sublacustrine fans are developed in the front of the delta.During the depositional period of the second member of the Nenjiang Formation,the R cycle began to develop due to the compression of the pacific tectonic domain;the source direction rotated 90°along with the eastern uplifting of the basin,and formed a series of east-west prograded and forced retrogradations.The prograding delta at high angel was developed in the interior of the sequence;the delta had a small front,a giant plain,and fewer underwater distributary channels,with the collapse at the foreslope,forming a series of slump fans.The slump fans can be divided into three types:discrete type,superimposed type,and fluid type.We built a whole"triad model"of the slump fan.Pointed out that the sequence of forced retrogradation formed by R cycle is a good structural mark of basin optimization,and rejected the viewpoint of"transgression"in the Nenjiang Formation of the Songliao Basin.
