--> Abstract: The Structure and Stratigraphy of Deepwater Sarawak, Malaysia: Implications for the Tectonic Evolution of the NW Borneo Contin; #90063 (2007)

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The Structure and Stratigraphy of Deepwater Sarawak, Malaysia: Implications for the Tectonic Evolution of the NW Borneo Continental Margin

 

Madon, Mazlan1, Kim Cheng Ly2, Robert Wong1 (1) PETRONAS, Kuala Lumpur, Malaysia (2) Petronas Carigali, Kuala Lumpur, Malaysia

 

The structural-stratigraphic history of the Sarawak deepwater is related to the tectonic history of the South China Sea. Seismic interpretation reveals a regional unconformity separating rifted basement from overlying undeformed bathyal sediments. Well data indicate that the unconformity is caused by uplift/erosion at ~16 Ma. This Mid-Miocene Unconformity (MMU) occurs over the entire NW Borneo margin, and is related to the Dangerous Grounds-Sabah collision during Mid-Miocene. The post-MMU sediments are marine muds and turbidites derived from the Sarawak shelf are ponded in depositional lows.

 

The pre-MMU section comprises half-grabens filled with fluvial and coastal-plain sediments. The synrift is correlated with the Paleocene-Eocene (pre ~32 Ma) rifting of the South China margin. The 32-Ma event is regarded as the break-up unconformity marking the initiation of sea-floor spreading. In Sarawak, this event is probably related the uplift of the Rajang foldbelt in the Late Eocene, following the collision of Luconia Block with Borneo. That collision resulted in a foreland basin to the north of the Rajang foldbelt. An interval of transparent seismic facies above the synrift is interpreted as transgressive, deep marine shale, representing the “flysch” phase of the foreland basin sedimentation. The bathyal marine shale interdigitates with, and passes upward into, fluvial and coastal plain sediments (the “molasse” facies) derived from the uplifted Rajang turbidites. The foreland basin sedimentation (Oligocene to Mid-Miocene) was interrupted by the deformation event at the MMU, after which the Sarawak basin evolved essentially as a passive margin post-Mid-Miocene times. The present-day NW Sabah margin is a useful analog for the pre-MMU foreland basin of Sarawak.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California