Print this pageMiocene Carbonate Platforms of the South China Sea Region: Tectonic Controls on Platform Inception and Termination
DOROBEK, STEVEN L
The inception and termination of Miocene carbonate platforms around the South
region are intimately linked to local patterns of deformation and differential
subsidence and to major tectonic events (e.g., onset of seafloor 
spreading
In
SCS, timing of ridge axis jumps, inversion events, onset of post-rift
subsidence). Comparison of platform histories with published sea level curves
shows that tectonics played an important, if not dominant, role in platform
evolution.
Miocene platforms from the northern and western sides of the SCS are located
on remnant fault-bounded highs that formed during earlier extension or
transtension. Many platforms were initiated at the onset of post-rift thermal
subsidence. Basement tilting is recorded within the internal stratigraphy of the
platforms as subtle divergence or convergence of stratal reflectors. Basement
tilting may be related to: 1) limited extension and rotation of fault-bounded
basement blocks during latest stages of rifting, 2) flexural loading by
Pliocene-Recent progradational siliciclastic she f facies, 3 the onset of
regional thermal subsidence, or 4) all of these factors. Differential tilting of
basement explains the backstepping behavior of some platform margins. Geometric
analyses of "growth strata" allow estimation of fault geometries and the amount
of fault block rotation. These analyses suggest that some platforms are
underlain by listric faults that flatten at depths between 10-20 km. Burial by
progradational shelf strata probably occurred after drowning, when platform tops
were at water depths of 200-400 m. This indicates that siliciclastic influx
probably was not an important factor in terminating many platforms.
Along the southeastern side of the SCS, synorogenic isolated platforms on the distal side of Miocene foreland basins are influenced by post-rift thermal subsidence and flexural subsidence of continental crust that is located northwest of Borneo and Palawan. The combined effects of post-rift thermal subsidence and flexural loading resulted in a highly modified flexural profile, rapid subsidence, and extremely rapid drowning of Miocene carbonate platforms across the foreland. Siliciclastic sediment shed from tectonic highlands in Borneo also contributed to platform termination.