The Philippines is made up of two major tectonic units,
namely, a) the stable rifted continental block to the west
and b) the mobile Philippine arc to the east. The
offshore West Palawan and the Sulu Sea region belong to
the rifted block that separated from mainland China as a
direct consequence of the opening of the South China Sea
basin in the Oligocene. The block, considered an
integral part of the Eurasian plate, is basically
continental in nature except for marginal basins created
along its edges.
The offshore West Palawan consists of three sedimentary
basins namely, Northwest Palawan, Southwest Palawan and
Reed Bank. The Sulu Sea region is composed of the
East Palawan and the Sulu Sea basins including the
sub-basins of Balabac, Bancauan and Sandakan. The
area of each basin ranges from 36,000 to 92,000 sq km (Sulu
Sea is bigger but it is partly covered by oceanic crust).
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