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ABSTRACT: Continental Margin Stratigraphy and Structure Offshore Vietnam, South China Sea Between 11° and 16°N

Sugiarta Wirasantosa, Joel S. Watkins

Seismic reflection profiles offshore Vietnam show a long, narrow rift basin trending NNW parallel to the margin. Sediments of more than 3.0 sec (twtt) fill the basin and overlie a pronounced unconformity. This unconformity, which appears to be a breakup unconformity, deepens to the SSE and overlies older, faulted prerift and synrift sediments.

Variation in postrift sediment thickness indicates that sedimentation rates varied throughout the area. Most of the time during deposition, sediment supply seems to have been low, which resulted in sigmoidal depositional patterns. Sea level was probably rising rapidly during this time as well.

Reflector dip throughout the study area indicates that sediment provenance is from the west. The shelf tilted progressively eastward during deposition and the sediments were distributed through submarine channels and one large canyon cut into shelf and slope. Seismic sequences show evidence of the channels and channel migratory paths. Slope sediments are faulted and slumped.

Sediment ages are mainly Oligocene and younger. The ages are consistent with opening of the South China Sea during this interval as suggested by a previous study of the Yingge basin to the north of the study area.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990