Evidences for syn-depositional tectonism in the Tertiary boulder beds of Batu Arang

Abstract

Based on a preliminary sedimentological and deformational study, the Tertiary Boulder Beds ofBatu Arang can be divided into two distinct sequences-the Red and the Gray Conglomeratic units, separated by an angular unconformity. The Red Conglomeratic Unit was deposited sub-areally, whilst the Gray Unit was deposited in a reducing, subaqueous environment. Numerous evidences for the interplay between tectonism and sedimentation are found within the Boulder Beds. These includes: 1. the immaturity of the sediments, compositionally and texturally; 2. cyclicity of the fining-upward sequences; 3. the occurrence of the intrabasinal angular unconformity between the Red and the Gray Units; 4. the presence of syn-depositional structures. These evidences suggest that the Boulder beds were deposited in a fault-controlled basin. The presence of post-depositional strike-slip faults suggest that tectonism outlasted sedimentation and together with the proximity of the basin to the Kuala Lumpur Fault zone, may suggest that the basin may have developed along a strike-slip fault.