DEPOSITION AND MIGRATION OF SEDIMENTS IN SUBMARINE CANYONS OF BAIYUN SAG AND THEIR EFFECTS ON GAS HYDRATE ACCUMULATION

A series of submarine canyons characterized by unidirectional sediment migration are investigated using a grid of high resolution seismic data in Baiyun Sag, northern South China Sea (NSCS). The unidirectional migrating canyon system and the dynamic bottom simulating reflectors (BSRs) are the result of the interaction between turbidity currents and bottom currents. The South China Sea Warm Current (SCSWC), an important bottom current in NSCS, is thought to be the main reason for the migration of canyons. The evolutionary history of a single canyon can be divided into three stages:erosion-dominated stage, erosion-deposition stage and the deposition-dominated stage. Four types of architecture elements consist of the fill of a single canyon, which are erosion surface (ES), basal lag (BL), mass transport deposits (MTD) and lateral inclined packages (LIP). Two distinct BSRs developed on each flank of the canyon because of the migration:the erosional flank undergoes more erosion than deposition, while the depositional flank is just the opposite. In consequence, the base of gas hydrate stability zone (BGHSZ) tends to move down on the erosional side of the canyon where sediments are removed by turbidity currents, while BGHSZ tends to move up on the depositional side where sediments become thicker.