Through seismic interpretation, the team observed a complicated structural feature in West Balingian Province which is probably a product of wrench-fault assemblage tectonic. Cycle I and older rocks were folded as a result of compressional force during the Late Eocene’s collision of Luconia block and Borneo Basement. During Oligocene, Sarawak margin subsided rapidly due to overburden Cycle I sediment infill from the uplifted of Rajang group. The uplifting happened again during Late Oligocene, top of Cycle I was eroded, forming unconformity at base Cycle II. From Cycle II upwards sequences, series of normal faults associated with graben structure were observed in the seismic data. These faults are probably result of extension component derived from wrench movement during Early Miocene to Pleistocene when South China Sea opened. The opening alongside with anticlockwise rotation of Luconia Block (Borneo) induced strike-slip movement at the study area which results in the wrench faulting (Hazebroek and Tan, 1993; Hazebroek et al., 1994). Major unconformities were also observed in seismic data at base of Cycle III resulted from uplifting of NW Balingian sub-province. All structures are interpreted using 3D seismic data, analyzed its age of deformation with the framework of regional tectonic history.


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