Sedimentary Characteristics and Depositional Model of the Crocker Submarine Fan: Evidence from Outcrop Areas in Sabah, Malaysia

[Objective]The southern continental margin of the South China Sea, as a convergent margin, records the closure process from the rift-drift-foreland tectonic stages. The Crocker Fan is a large deep-water submarine fan formed during the Oligocene to Early Miocene following the Sarawak collision. [Methods]This study systematically summarizes the sedimentary characteristics of the Crocker Fan based on observations from 10 outcrop profiles in the Sabah region of Malaysia. [Result]Research indicates that the West Crocker Formation is primarily composed of unmetamorphosed submarine fan and deep-sea muddy sediments, roughly equivalent to the Miri Zone in the northern Borneo collision belt. It covers an area of over 25,000 km2 and is distributed along the coastal zones of Sarawak and northern Sabah. The Crocker Fan is an unconfined deep-water submarine fan. Due to scattered outcrops and a lack of seismic data, it is inferred to be part of a large submarine fan complex formed along the collision zone. The fan is mainly composed of sandy high-density turbidites consisting of fine- to medium-grained sandstones and argillaceous low-density turbidites composed of siltstones, with occasional coarse sandstone or gravel-bearing mass transport deposits. The sedimentary facies include tens-of-meters-thick turbidity channels, medium-to-thick turbidity channel/levee deposits, lobe deposits, and thin sheet sands interbedded with mudstones. Incomplete Bouma sequences are observed in the lobe and sheet sand deposits, with sole marks and trace fossils being very common. Additionally, abundant plant debris is visible on the bedding planes of the interbedded thin sheet sands and mudstones, and vitrinite bands are occasionally observed, indicating that coastal peat swamps in a narrow shelf setting were transported into deep-water deposits. [Conclusion]These well-exposed profiles provide excellent examples of submarine fan deposition in a narrow shelf environment. The research findings hold significant importance for understanding the dynamics of the South China Sea continental margin and the study of deep-sea reservoirs.