Sedimentology and Depositional Environment of the Semantan Formation, Central Pahang

The name of Semantan Formation was erected by Jaafar (1976) for a succession of predominantly carbonaceous shale with rhyolitic tuff of Triassic ages that outcroped in the Karak-Temerloh area. A detailed study comprising sedimentology was carried out on five well-exposed outcrops in this area to characterize the facies and facies association of the Semantan Formation in order to propose a new depositional model. The main facies recognized in the field include thick amalgamated sandstone, interbedded sandstone-shale, chaotic mixture of sandstone-mudstone, lenticular bedded of sandstone-shale, fine laminated siltstone-shale and shale dominated. The interpreted facies associations consist of channel levee, channelized lobe, slumps deposits and shale dominated. The debris flow and turbidity current are identified as main depositional process in Semantan Formation. As a result, the sedimentary succession is classified as sand-rich submarine fan environment which divided into three major zones (1) inner fan for channel levee deposits, (2) mid-fan consists of channelized lobe deposits and (3) distal part of the fan dominated by shale or intercalated with siltstone.