Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a se...Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation(KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS,the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity,its ichnologic signature, and the depositional regime change refer to a higher-resolution(i.e., lower-order)sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.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 computerized geochemical modeling, a useful tool to understand the diagenetic processes influencing the quality of hydrocarbon reservoirs, is performed by using different modules of computer codes based on the the...The computerized geochemical modeling, a useful tool to understand the diagenetic processes influencing the quality of hydrocarbon reservoirs, is performed by using different modules of computer codes based on the thermodynamic and chemical kinetic principles and their associated parameters. As observed in the reservoir lithofacies deposited from the marine sediment-gravity flows, a case study of diagenesis is presented here from the Espírito Santo Basin in southeastern Brazil. The study uses the Geochemist＇s Workbench（GWB～（TM））, PHREEQC～（TM） and TOUGHREACT～（TM） computation packages. The comparison of performances of these packages demonstrates the convergence of results from the software-based geochemical modeling with the petrographic observation of dissolution, albitization, kaolinization, and the precipitation of calcite and dolomite. Moreover, with limited data points, e.g., the sedimentary petrographic data acquired from limited number of boreholes, the computer simulation establishes itself to be a powerful quantitative method estimating the degree and type of diagenetic alteration of turbidite reservoir bodies in contact with a source of saline-water influx associated with salt tectonics.Therefore, using the limited petrographic data points, the geochemical computer-simulation method can even be utilized and extrapolated for areas where similar geological context is interpreted but no borehole data are available. Hence, porosity of turbidite reservoir lithofacies can be predicted in relation to the spatial distribution of dissolution, kaolinization, and albitization of feldspars and authigenic carbonate precipitation.展开更多
基金Science and Engineering Research Board (SERB), Government of India (Grant # CRG/2018/000259 to SDG)Industrial Research and Consultancy Centre (IRCC), IIT Bombay (Seed Grant # RD/0517-IRCCSH0-035 to SDG)Council of Scientific and Industrial Research (CSIR) (doctoral scholarship for AS),University Grants Commission (doctoral scholarship for KC),IIT Bombay and Ministry of Education of India (doctoral scholarship for MD)。
文摘Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation(KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS,the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity,its ichnologic signature, and the depositional regime change refer to a higher-resolution(i.e., lower-order)sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.
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.
文摘The computerized geochemical modeling, a useful tool to understand the diagenetic processes influencing the quality of hydrocarbon reservoirs, is performed by using different modules of computer codes based on the thermodynamic and chemical kinetic principles and their associated parameters. As observed in the reservoir lithofacies deposited from the marine sediment-gravity flows, a case study of diagenesis is presented here from the Espírito Santo Basin in southeastern Brazil. The study uses the Geochemist＇s Workbench（GWB～（TM））, PHREEQC～（TM） and TOUGHREACT～（TM） computation packages. The comparison of performances of these packages demonstrates the convergence of results from the software-based geochemical modeling with the petrographic observation of dissolution, albitization, kaolinization, and the precipitation of calcite and dolomite. Moreover, with limited data points, e.g., the sedimentary petrographic data acquired from limited number of boreholes, the computer simulation establishes itself to be a powerful quantitative method estimating the degree and type of diagenetic alteration of turbidite reservoir bodies in contact with a source of saline-water influx associated with salt tectonics.Therefore, using the limited petrographic data points, the geochemical computer-simulation method can even be utilized and extrapolated for areas where similar geological context is interpreted but no borehole data are available. Hence, porosity of turbidite reservoir lithofacies can be predicted in relation to the spatial distribution of dissolution, kaolinization, and albitization of feldspars and authigenic carbonate precipitation.
