Jurassic-Cretaceous fluvial channel and floodplain deposits along the Karak-Kuantan Highway, central Pahang (Peninsular Malaysia)

Abstract

A fluvial succession of probable Jurassic-Cretaceous age is well exposed at Km 160 along the Karak-Kuantan highway, central Pahang. Although the exact age of these rocks is unknown, the depositional environment of the rocks, and their relatively unmetamorphosed nature and low structural dips compared to surrounding rocks, suggest that they are equivalent to the 'post-orogenic' continental deposits, generally referred to as the Jurassic-Cretaceous Gagau Group. Such outcrops are rarely found preserved anywhere in Peninsular Malaysia, and if conserved, provides a good locality for the study fluvial deposits. The succession comprises fining-upward channel fill sands and muds, intercalated with red and green overbank and floodplain mudstones. There are four major sandbodies, three of which represent fining upward channel/ channel margin sands (>2 m thick), while the fourth consists of at least four tabular/sheet-like sandstones (1.5 m thick) interpreted as crevasse-splay sheet sand deposits. Their facies characteristics suggest that the sediments were deposited in a low-lying meandering channel-floodplain system. The co-existence of red and green mudstones in the floodplain facies suggest that there could be seasonal/climatic fluctuations that affected the geochemical conditions in the basin.