Variability and Process Sedimentology of Thick Massive Sandstone Facies of West Crocker Formation, NW Sabah, Borneo

Abstract

The sand rich, deep water facies association of the West Crocker Formation has been ascribed to four principal facies elements viz a metre scale, thick, massive sandstone facies; thin tabular, planar to ripple laminated sandstone –mudstone facies; sand or mud rich debris flow with occasional slump facies; and lastly plane laminated mudstone facies. The predominant facies, thick massive sandstone facies, which is apparently massive, presents significant variability. Six sub facies of the massive sandstone facies attributed to different processes of occurrence are: i. Massive, structureless sandstones ii. Sandstones with faint, crude planar laminations or cross stratifications iii. Sandstones with random floating clasts iv. Sandstones with fluid escape and dish structures v. Sandstones with convolute lamination vi. Sandstones with rugose upper surface and upward sand injectites. The aim of this article is to exemplify that simplified, apparently massive, thick sandstone units have different processes of occurrence. All the details and distinctive observed sedimentary structures, bed thickness, grain size, grain and matrix composition, all allow the finer distinction of these massive to apparently massive sandstone associated with gravity flow deposits from turbulent to truly laminar flow processes in aspect of process sedimentology for sand rich deep water depositional system.