Sedimentary facies analysis of a thin-bed-dominated turbidite succession in the Miocene Temburong Formation, Kampung Bebuloh, Labuan Island, Malaysia

Abstract

Thin-bedded turbidites are important hydrocarbon-bearing reservoirs in many mature fields throughout the world. The type of turbidite depositional setting strongly influences vertical and horizontal continuity of the reservoir. However, distinguishing between lobe and levee associated thin-bedded turbidites remains challenging due to their generally similar facies characteristics. This study aims to contribute some insights to this problem by conducting a detailed bed-scale facies analysis on the Early Miocene Temburong Formation exposed at Kampung Bebuloh, Labuan Island, Malaysia, which may uncover features that can help in differentiating between both depositional types. Six facies are recognized in the Temburong Formation, which are interpreted as low density turbidites (F1–F4), hybrid event beds (F5), and sustained turbidites (F6). Detailed facies and ichnology analysis reveal features which are consistent with a lobe fringe deposit rather than levee-associated environment interpretation, including tabular bed geometries, presence of hybrid event beds, and the absence of thick-bedded channel-fill sandstones. Five facies associations are identified and interpreted as representing sub-environments within an overall lobe depositional setting. A diverse trace fossil assemblage, comprising the Nereites ichnofacies is consistent with a deep marine environment. Further identification of the Paleodictyon and Nereites sub-ichnofacies indicates a distal turbidite system setting, most likely lobe fringe. Based on the thick accumulation of FA2 and FA3 and no distinct observable vertical trend, the Early Miocene Temburong Formation in Labuan is interpreted as turbidites deposited at the fringes of lobe complexes rather than a single lobe fringe. Earlier works into the Temburong Formation in SW Labuan proposed a middle slope to proximal basin floor setting where the thin-bedded intervals were interpreted as potentially representing either levee deposits or the fringes of confined lobe deposits. Conversely, the Temburong Formation at Kampung Bebuloh exhibits characteristics of an unconfined lobe setting, suggesting an evolutionary change in depositional conditions over time.