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.