Sediment Partition In Rift Basin: Processes And Responses

Sediment partition processes and responses analysis have been the subject of increasingly intense study in recent years,but are still far away from detailed understood.This study uses core data,well log data,3D seismic data,thin sections and grain size data to investigate the sequence distribution,sandbody types and distribution,fan architecture and source to sink system which reveal the variability of sediment partition in a single rift lacustrine basin.Subsiquently,based on the comparisons of sequence distribution,sandbody evolution between the Nanpu Sag and the Dehui Sag,this study describes the spartial and temporal variations of sediment partition between different rift lacustrine basins.Finally,this study discusses the controls of fault evolution,tectonic subsidence rate and sediment supply on the processes and responses of sediment partition in rift lacustrine basin.The analysis of sediment partition variations in a single rift lacustrine basin reveals that the area and distribution of accommodation show spartial and temporal variations.The area of the sequence increased from the early stage to the late stage,while the subsidence center and depocenter developed from isolated to uniform and migrated from north to sourth.The sequence architecture of different structure belts of the same period shows variations.Four types of sequence architecture are identified,which are fault-cliff type,fault-slope type,relay ramp type,fault-terrace type.The sandbody distribution also shows spartial and temporal variations.The fan size increased from down to up whereas the fan type is stable.The sediment pathway of different structure belts shows variations.The paleogeomorphy controls the sediment pathway of the Laoyemiao and Beipu structure belts.The transverse anticline and antithetic fault steps control the sediment pathway of the Laoyemiao,while the rolling anticline and normal fault steps control that of the Beipu.The fan architecture shows vertical variability within the same structure belt,which can be evidenced by that the channel deposits proportion,multi-story channel number,channel scale,channel vertical stacking density increase upward,whereas mouth bar and overbank deposits proportion decrease upward.Based on the quantitative measurement of different topography units of source to sink system and analysis of sediment partition,three source-to-sink systems which consist of the Laoyemiao,Beipu,No.2 systems are reconstructed and their spartial and temporal variations are also be compared.The accommodation distribution and sandbody evolution of different rift lacustrine basins also show differences.The depocenter and subsidence center are isolated and adjacent to the boundary faults,while the fan type show strong spartial and temporal variations in the Dehui Sag.Tectonic movements play significant role in controlling the sediment partition in rift lacustrine basin.The growth and evolution of boundary fault control the catchment size,sediment input,accommodation size and distribution.The secondary structure belt and secondary faults of the sink control the sediment pathway.The subsidence rate shows a negative relationship with the channel vertical stacking density.High subsidence rate corresponding to a fan architecture of channel and mouth bar dominant whereas low subsidence rate corresponding to a channel dominant fan architecture.The catchment size and relief control the sediment supply and then control the channel scale and fan size.Fault evolution controls the morphological evolution and variations of the source to sink system.Afrormationed results enriched the analysis of source to sink and relations between tectonics and sediment partition in rift basins and have a significant contribution to hydrocarbon exploration.