Architecture and depositional processes of sublacustrine fan systems in structurally active settings: An example from Weixinan Depression, northern South China Sea

• DOI: 10.1016/j.marpetgeo.2021.105380
• Publication Date: 2021-10-19T16:59:22Z
• Authors: Entao Liu; Hua Wang; Songqi Pan; Chunyu Qin; Ping Jiang; Si Chen; Detian Yan; Xiaoxia Lü; Zhenhua Jing
• Keywords: Bedding; Turbidity current

Abstract Sublacustrine fans developed in structurally active settings are commonly characterized by complicated depositional characteristics, which create great challenges to hydrocarbon exploration. To advance understanding their sedimentary architecture and depositional processes, a large-scale sublacustrine fan system in the Eocene Weixinan Depression, northern South China Sea has been identified and investigated through the comprehensive analysis of 3-D seismic, well-logging, and core data. This fan was deposited during a lake-level falling stage, covering an area of 55 Km2. It can be divided into two sections in the vertical direction by the sedimentary characteristics. The lower section mainly consists of thin layers of well-sorted fine sandstones with parallel bedding, which are interpreted as deposits of turbidity currents. By contrast, the upper section comprises thick layers of gravelly coarse sandstones with various deformation structures and widespread floating clasts, which should be the deposits of cohesive debris flows. Provenance analysis suggests that the development of complicated sedimentary characteristics has a close relationship with the occurrence of multiple sediment supply directions. The lower section was sourced by the western delta with long-distance transported well-sorted sediments, while the northern fan delta sourced the upper section with short-distance transported coarse-grained sediments. Its depositional process was mainly controlled by paleo-geomorphology, sediment supply, and relative lake level changes. The lower section, controlled by the flexure slope belt, is a typical sand-rich sublacustrine fan characterized by the low gradient (