Bulletin of the Geological Society of Malaysia, Volume 41, Dec. 1997, pp. 61 – 84
Petronas Research & Scientific Services Sdn. Bhd., Lot 3288/3289, Kawasan Institusi Bandar Baru Bangi, 43000 Kajang, Malaysia
Abstract: The sedimentological features of lower to middle Miocene sedimentary rocks in the northern part of Labuan Island, offshore west Sabah, are described. The Temburong Formation (or “older Setap Shale”) forms the core of the Labuan Anticline. Excellent exposures of the Temburong Formation occur along the coast near Tg. Layang-Layangan, where the formation consists of an overall regressive (shallowing) sequence of heterolithic facies deposited in environments ranging from relatively deep water and unstable slopes to shallow nearshore settings.
The Belait Formation crops out in the northern part of Labuan as a prominent strike ridge that extends from Tg. Kubong to Tg. Layang-Layangan and in the eastern part of the island from Tg. Kubong to Tg. Batu, essentially forming the two limbs of the northeastward-plunging Labuan Anticline. The sedimentology of the Belait Formation is described based on field work in the Tg. Kubong area, which included detailed logging of a major road-cut at the Chimney. Here, the basal Belait is a sequence of conglomerate and sandstone laid down by fluvial systems that were eroding into the uplifted Temburong Formation. A transition from high-relief low-sinuosity to low-relief high-sinuosity fluvial system is indicated by the upward-decreasing grain size and pebble content in the channel fill deposits, and by the occurrence of coal in the overlying alluvial plain deposits, which are exposed on Bukit Kubong. The fluvial succession passes upwards into a transgressive (deepening) sequence of nearshore and offshore shallow marine sandstone and mudstone dominated by hummocky cross-stratified sandstone intercalated with shale. Syndepositional deformational structures are a common feature of the shallow marine deposits in both the Temburong and the Belait Formations which resulted from sedimentation on the once actively-deforming continental margin of NW Sabah.