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TitleThree dimensional seismic anatomy of multi-stage mass transport deposits in the Pearl River Mouth Basin, northern South China Sea: Their ages and kinematics
AuthorSun, Q; Xie, X; Piper, D J W; Wu, J; Wu, S
SourceMarine Geology 2017.,
Alt SeriesEarth Sciences Sector, Contribution Series 20160098
Mediapaper; on-line; digital
File formatpdf
AreaSouth China Sea; Pearl River Mouth; China
Lat/Long WENS 114.0000 118.0000 21.0000 18.0000
Subjectssediment transport; fluvial transport; seismic surveys, marine; seismic data; seismic surveys; bathymetry; submarine features; turbidites; silts; seismic reflection data; submarine morphology
Illustrationslocation maps; seismic reflection profiles; seismic profiles; graphs
ProgramMarine Geohazards, Public Safety Geoscience
AbstractThree superimposed Quaternary mass transport deposits (MTD1, MTD2 and MTD3) in the Pearl River Mouth Basin of northern South China Sea are identified, using high-resolution three dimensional seismic data. This study dissects the three stacked MTDs in detail and demonstrates their kinematics, formation times and controlling factors. They are bounded upslope by steep scarps 30-120 m high at the seabed, at a water depth of ~2500¿2900 m, deepening to the southeast. Each MTD is characterized by linear grooves on their base and by chaotic seismic reflections with complex internal structures, such as remnants, rotational blocks, and imbricated thrust faults. The younger MTDs directly overlie and in places erode the older ones and they are separated by basal shear surfaces (negative high-amplitude seismic reflectors).The linear grooves and internal structures of MTDs indicate that the sediments mainly flowed from the NW to SE in the study area but the distal parts of MTD2 and MTD3 turned and flowed to the SW. MTD1, MTD2 and MTD3 are dated to 0.19 Ma, 0.50 Ma and 1.59 Ma, respectively, based on seismic correlation to the synthetic seismogram of ODP Site 1146. Free gas is characterized by enhanced seismic anomalies in sharp contact with the surrounding strata. Coarse-grained sediments characterized by high-amplitude seismic reflections, likely turbidites, are observed below the MTDs. Internal structure demonstrates that MTD2 is a spread and MTD3 is a rotational slump, both terminating upslope at the regional line of scarps. The scarps are controlled by both the underlying structures (such as basement highs and related faults) and the distribution of weak layers, probably gas-bearing thin turbidite silt beds, that do not extend farther upslope. During earthquake shaking, failure occurred along these weak layers and the headscarps are interpreted to represent the upslope limit of those weak layers. Similar lower slope¿rise MTDs, of local origin, may be widespread elsewhere, but would be difficult to distinguish without 3-D seismic data.
Summary(Plain Language Summary, not published)
The geometry of several lower slope landslides indicates that their distribution is controlled by the presence of thin turbidite silts, probably gas charged. They emphasise the point that large marine landslides may be initiated on very low gradients.