Sedimentary characteristics of braided-meandering distributary channels in shallow-water delta of Huagang Formation in the central and southern parts of Xihu Depression
The upper section of Huagang Formation in the central Xihu Depression is an important exploration layer series for structural-lithologic oil and gas reservoirs.The study area is mainly composed of shallow-water delta sedimentation,where significant differences exists in the types and scales of sand body facies in the vertical and horizontal directions.Through the analysis of sedimentary backgrounds such as ancient water bodies,paleogeomorphology,and paleoclimate of Huagang Formation,it is believed that the SQ3 sequence of Huagang Formation developed shallow-water delta plain distributary channel sediments,which were controlled by factors such as mid-term base level,micro ancient landforms,and sediment supply.The distributary channels in delta plain exhibited braided and meandering characteristics.The research results indicate that:①During the rising and falling periods of the mid-term base level,the sediment is mainly provided by the northeast source,with a small amount from the northwest.The accommodation space is relatively small.The low terrain areas are mainly dominated by braided distributary channels,with coarse sediment grain size and development of multi-stage scouring surfaces and retained gravels,as well as the development of sand bodies of channel bars.The logging facies are mainly box shaped,and the cross-section presents a thick and wide trough shape.②During the transition period of mid-term base level,the southwest source is dominant,while the northeast is weakened,and the accommodation space is relatively large.The low terrain areas are mainly characterized by meandering distributary channels,with fine sediments and tearing mud and gravel on the erosion surface.The logging facies are mainly bell shaped,and the cross-section presents an asymmetric lens shape.
the central and southern parts of Xihu DepressionHuagang Formationshallow-water delta plainbraided-meander distributary channel
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