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Syn-Tectonic Depositional Signatures in Shelf to Fluvial Sequences of a De-Forming Margin: the Temburong and Belait Formations (Lower-Middle Miocene), Labuan Island, Malaysia

Madon, Mazlan 1; M Som, M Rapi 1; Abd Kadir, M Fauzi 1; WM Sulaiman, WM Khairul 1
1 Petronas Research Sdn Bhd, Kajang, Malaysia.

Sedimentary sequences deposited in actively deforming margins provide a record of the in-terplay between sea-level change and subsidence/uplift. This paper describes a Miocene suc-cession from the island of Labuan, eastern Malaysia, where sedimentary features indicate rapid base-level changes that were strongly influenced by tectonic uplift. Labuan is one many anticlinal structures produced by compressional tectonics associated with foreland basin de-velopment following continental collision and the formation of the Deep Regional Uncon-formity (DRU) in the Middle Miocene. This unconformity separates deep to shallow marine Temburong Formation from overlying fluvial to shallow marine Belait Formation. Onshore in West Sabah, the DRU is the peneplanation surface above the outcropping West Crocker For-mation turbidites. Like other regional unconformities in the basin, the DRU is a syntectonic unconformity which gradually becomes conformable basinwards in offshore NW Sabah ba-sin.

Depositional features in the shelf and fluvio-marine deposits above and below the DRU show evidences for syn-tectonic sedimentation, which include: (1) evidence for rapid shoaling to-wards the upper part of the Temburong Formation below the DRU, suggesting penecontem-poraneous growth of the Labuan anticline (2) pervasive syn-sedimentary deformation and remobilization, including slumps, micro-faults, and load structures, suggesting gravitational instability induced by the tectonic steepening of the depositional gradient, (3) upward-increase in current-generated angle-of-repose stratification in a storm- and wave-dominated shelf succession, and
4 a relatively thin fluvial to shallow marine transition above the DRU, implying rapid deepening due to the steepening depositional surface, coupled with rising sea level.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009