Observations on Sediments and Deformation Characteristics,
Sarawak Foreland, Borneo Island
SSB/SSPC Shell Exploration Asia Pacific
Locked Bag 1, 98009 Lutong
Sarawak, Malaysia
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To be published in the upcoming Q1/2008
Bulletin of the Geological Society of Malaysia
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Abstract: Based on some 120 days of GPS-calibrated fieldwork by land and boat, attempts are made to clarify the geologic picture of the Oligocene-Neogene Sarawak Foreland, in context with the older “Rajang” sequences. Sediments of the Sarawak Foreland are molasses deposits and consist of NW-prograding, and shallowing/ coarsening -upwards sequences. Tectonics appear to be area-specific. Amount and style of deformation vary strongly between the areas of Luconia and the “Baram Delta.” Inversion, folding, reverse faulting, and thrusting can be related to a NW/SE compressive stress field that culminated at the Late Miocene/Pliocene boundary. The contact between the mildly folded Oligocene-Neogene foreland, and the intensely folded inner-Borneo KK-Eocene Rajang/Crocker mountain belt was mapped on satellite pictures and calibrated in two localities. Both mountain belt and foreland area were welded together at the end of the Miocene. The potential for alpino-type nappe tectonism within the KK-Eocene mountain belt is discussed. A case is made for one single boundary fault/thrust front running from Sarawak to Sabah.
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