Three dimensional seismic anatomy of multi-stage mass transport deposits in the Pearl River Mouth Basin, northern South China Sea: Their ages and kinematics

Three superimposed Quaternary mass transport deposits (MTD1, MTD2 and MTD3) in the Pearl River Mouth Basin of the northern South China Sea are identified using high-resolution three dimensional seismic data. This study dissects the three stacked MTDs in detail and interprets their distribution based on antecedent bathymetry and their kinematics from identified structures and sedimentological models. Each MTD is characterized by linear grooves at its base, by chaotic seismic reflections and complex internal structures, such as remnant, rafted and faulted blocks. The linear grooves and internal structures of MTDs indicate that the sediments mainly flowed from the NW to SE in the study area. Moreover, internal structures suggest that MTD2 is a spread and MTD3 is a rotational slump, both terminating upslope at a regional linear escarpment. MTD1 is interpreted as the distal part of a larger MTD. The ages of MTD1, MTD2 and MTD3, based on seismic correlation with ODP Site 1146, are 0.54 Ma, 0.79 Ma and 1.59 Ma respectively. High-amplitude seismic reflections observed below the MTDs are interpreted as coarse-grained turbidites. Headscarp locations are controlled by both the underlying structures (such as basement highs and related faults) and the distribution of weak layers that are probably gas-bearing thin turbidite silt beds. This study provides precise ages of stacked MTDs in the northern South China Sea for the first time and at least locally provides clear evidence for the flow directions and controlling factors of the stacked MTDs. Similar lower slope-rise MTDs, of local origin, may be widespread elsewhere, but would be difficult to distinguish without 3-D seismic data.