Contrasting
Controls on Deep-Water Sediment Delivery on the Periphery of the South China
Sea
Dickson, William G.1, James W. Granath2, Mark E. Odegard3, Janice M. Christ4
(1) Dickson International
Geosciences (DIGs), Houston, TX
(2) Midland Valley
Exploration, Golden, CO (3) Grizzly
Geosciences, Sugar Land, TX (4) Geological
Consultant, The Woodlands, TX
Deep-water sand bodies were deposited
around the South China Sea (SCS) margin in distinctive tectonic environments
distinguished and mapped on various inversions of gravity data trained by
published examples. Three selected systems lie in tectonically defined
compartments of sediment thicks with
onshore-to-offshore distributary patterns often channelised into corridors by coastline segmentation.
The Pearl River Mouth Basin (PRB) sand
delivery system was established probably in earliest Tertiary. Since the
Oligocene, sands have been confined to one segment of the south China coast by NW-SE
accommodation structures. The shallow to deep transition was apparently defined
by relative sea level so the sediment thick comprises stacked sand systems with
outboard components composed of distal sands periodically re-deposited in
deeper water.
The Northwest Borneo system has been
continually deformed, first by convergence of Borneo with the SCS margin and
then by gravity-driven toe thrusting. Deltaic sediments of this margin
northeast of the Luconia platform overtop the
convergent system. Most shallow-water deltaic sediment was concentrated near
the coast on the southeast flank of the sediment thick, while deep-water fan
bodies were trapped behind the distal toe thrust system to the northwest. The accretionary prism's Neogene
portion is therefore composed bilaterally of deltaic sediments on one side and
fan complexes on the other.
In southern East Vietnam offshore, deep-water
fan systems appear to dominate sediment fill in the narrow,
continental-borderland-related Phu Khanh basin. Sediment input was localized across a narrow
continental shelf into the also narrow, strike-slip related basins with little
if any shallow-water architecture developed.