The geology of Sarawak deepwater and surrounding areas

Abstract

A geological and geophysical investigation of several key transects ofthe 1989 vintage seismic grid in the Sarawak deepwater was conducted in order to understand the sedimentation history and structural geology of the area. In the study area, two tectonostratigraphic provinces can be recognised, namely the North Luconia and West Luconia Provinces. The deep sedimentary basin of North Luconia is filled with 7-8 km of Tertiary sediments and are characterised by NNE-SSW trending extensional fault bounded features, buried hills and local occurrences of forced folds. On the eastern boundary, a major, NNE-SSW trending basin boundary fault separates it from the Northwest Sabah Platform. The latter by contrast is an attenuated crustal terrain characterised by NE-SW trending rift systems and generally thinner sedimentary cover of about only 2-4 km thick. To the southeast, the West Luconia Province which is a thick sedimentary basin with up to about 13 km of sediments, contains a very thick pile of post mid Miocene sedimentary section and is characterised by E-W trending growth faults and °a series of slumps and toe thrusts formed by gravity gliding. These overlie an older normal-faulted section at a mid Miocene unconformity. Generally, the crustal extension in the South China Sea and peripheral areas have generated various patterns of rift orientation and extensional axes. In North Luconia the NNE-SSW trending extensional elements parallel some of the basin axes in the N am Con Son Basin, offshore Vietnam. Finally, based on sequence stratigraphic framework, up to five sub-megasequences are recognised in the Sarawak deepwater. The age determination from well controls and correlation with the episodic crustal rifting and seafloor spreading in the South China Sea Basin has provided some insight on the tectonic evolution.