Sedimentology of the Jalan Salaiman and Bukit Melinsung outcrops, western Sabah: is the West Crocker Formation an analogue for Neogene turbidites offshore?

Abstract

Outcrops of the West Crocker Formation in western Sabah are dominated by coarse-grained sandstones interbedded with shale, although numerous bedding-plane thrust faults that form preferentially in the shales and weathering that favours exposure of sandstone suggest that the actual sand-shale ratio may be significantly lower. The sandstones occur as amalgamated units with individual beds that are generally 1-6m thick within 25-65 m thick parasequences. Most sandstones are massive and display partial Bouma sequences. The sands are texturally immature with a high proportion of rock fragments and poorly sorted. Their sedimentary structures and texture are consistent with a short transport path down a relatively steep slope and then rapid deposition from collapse fall-out in high density turbidity currents. In the outcrops studied in detail, comprising nearly 500 m of succession some of which is laterally continuous up to 500 m, most beds are sheet sands and a few are lobate and there is no evidence of channeling. The bed geometries, texture and depositional mechanism all suggest relatively small lobes that coalesced to form a sand-rich slope apron.Palaeocurrent directions are consistently to the north, indicating a transport direction that is oblique to the northeast-southwest marginal basin. This suggests that the West Crocker strata were derived from nearby Rajang Group sediment, possibly in response to the initial phase of the uplift that formed the Deep Regional Unconformity. The tectonic setting, facies distribution, stratigraphic architecture, sand body orientation, texture and sorting of the West Crocker turbidites are all significantly different from those of the Neogene turbidites offshore and, therefore, they are a poor analogue for the younger sands.

The structural evolution of folds in a deepwater fold and thrust belt – a case study from the Sabah continental margin offshore NW Borneo, SE Asia

“…This collision history is reflected in significant compressional deformation documented onshore northern Borneo in folded sedimentary units of late Early Miocene age (e.g. Tongkul, 1994;Sandal, 1996;William et al, 2003). Subsequently, northern Borneo experienced further compression as documented onshore in folded sedimentary units of Middle to Late Miocene ages (e.g.…”

Organic petrographic characteristics of the Crocker Formation, NW Sabah, Malaysia

“…The NE-SW trending elongated basin in which the West Crocker sediments were deposited was created by the perpendicular NW-SE compression in the Late Cretaceous-Early Eocene, and is related to the opening of the Southwest sub-basin of the South China Sea Basin (Tongkul, 1994). The sediments were probably derived from the south, as indicated by consistent northwards palaeocurrent direction (William et al, 2003). An eastward source is considered unlikely, as it is insufficient for the Crocker Formation and Rajang Group (Crevello, 2002).…”

“…The West Crocker Formation consist mainly of coarsegrained sandstones interbedded with shale (William et al, 2003). This formation is classified as turbidite deposits and considered an unattractive exploration target due to its poor quality reservoir sands and lack of hydrocarbon (Crevello, 2002).…”

A tuffaceous volcaniclastic turbidite bed of Early Miocene age in the Temburong Formation of Labuan, North‐West Borneo and its implications for the Proto‐South China Sea subduction in the Burdigalian

“…A smectite‐rich tuff bed is described from the Temburong Formation on the southern part of the island of Labuan, off the Malaysian coast of Sabah in Borneo (Figure 1). The Temburong Formation is a deep water turbidite deposit which is the time equivalent of the better known West Crocker Formation (WCF), one of the largest Palaeogene to Neogene sedimentary deposits of South‐East Asia (Crevello, 2006; Hattum et al, 2013; William et al, 2003; Zakaria et al, 2013). The smectite‐rich bed is interpreted as an altered volcaniclastic turbidite deposited in deep water.…”