Architecture, evolution history and controlling factors of the Baiyun submarine canyon system from the middle Miocene to Quaternary in the Pearl River Mouth Basin, northern South China Sea

Abstract Since the middle Miocene, a series of northeastward unidirectionally migrating canyons (UMCs) have developed in the Baiyun Sag, Pearl River Mouth Basin. Seven closely spaced submarine canyons have been investigated in detail under the integrated analysis of 2D/3D seismic and well data. Five architectural elements of canyon-fill deposits are identified: basal lag (BL), slump and debris-flow deposits (SDFDs), canyon confined sheets (CCSs), laterally inclined packages (LIPs) and channel-levee complexes (CLCs). Three evolutional stages of canyon development are recognized for the first time: (1) the middle Miocene stage, during which U-shaped, slope-confined vertical aggradation-dominated UMCs developed; (2) the late Miocene stage, during which U-shaped, shelf edge-indented lateral migration-dominated UMCs developed; and (3) the Pliocene-Quaternary stage, during which slope-confined vertical aggradation-dominated UMCs developed. Extensive slope failures which developed during this final stage had a close relationship with the extensive release of focused fluid flow. The UMCs identified in all of these three stages suggest that along slope bottom currents have been active in the Baiyun Sag since the middle Miocene. Evolution of the Baiyun canyon system was likely controlled by sediment supply, regional tectonic activity, sea level fluctuations and paleo-ocean current. Based on the contrast of UMCs in this study area, two different types of UMCs are identified. The first type of UMCs with their heads coupling with areas of high coarse-grained sediment supply, usually indent the shelf edge, generating canyon-fills with sand-rich BL in the bottom grade upward into SDFDs and finally into LIPs, and downslope submarine fans/aprons. The second type of UMCs with their heads coupling with areas of starving sediment supply, usually do not indent the shelf edge, generating canyon-fills with mud-rich BL in the bottom grade upward into SDFDs, thin CCSs and CLCs and finally into LIPs, which are dominated by retrogressive mass wasting processes, exhibiting highly aggradational morphologies, and absence of downslope fans/aprons. Both these two types of UMCs form U-shaped heads and result from the interaction between gravity flow and bottom current, however, the first type of UMCs are influenced by the surface current (mainly the South China Sea Warm Current) and the intermediate water current, but the second type of UMCs are only influenced by the intermediate water current.