Bulletin of the Geological Society of Malaysia, Volume 36, Dec. 1994, pp. 67- 80
Petronas Research & Scientific Services Sdn. Bhd., Lot 1026, PKNS Industrial Estate, Ulu Kelang, 54200 Kuala Lumpur
Abstract: The regional elements in the west-central margin of the Malay Basin largely comprise a platform area and a hingeline zone which runs parallel (NW-SE) to the basin margin. The Tertiary basement of this margin is divided into three structural units based on fault trends and basement structural contours. The northern unit is characterised by fault trends controlled by basement highs. Central unit represents a zone of fault bifurcation. Within the southern unit, there is a fault zone which is aligned to the Dungun graben. The causative maximum horizontal compression acted on the pre-Tertiary basement is in the 20°-40° direction.
Right lateral wrenching could have occurred at the west-central margin of the Malay basin as early as Jura-Cretaceous and continued till pre-Oligocene. It has initiated the formation of Tok Bidan Graben and is shown by the occurrence of basement faults transecting the Jura-Cretaceous as well as pre-Oligocene sediments in the Tok Bidan Graben. Tok Bidan Graben resembled a rhomboid pull apart basin by right lateral wrenching. The continual right lateral wrenching during pre-Oligocene could have initiated the formation of NW -SE trending Dungun faults and its associated half grabens. The Dungun graben is located at the south-east end of the Dungun faults. This graben is also a right lateral wrenched rhomboid pull apart basin. The location of this graben at the south-east end of the Dungun faults suggested the movement of the Dungun faults in a dextral sense.
Right stepping en echelon faults within ?Miocene sediments in the Dungun Graben suggested a reversal of wrench movement during ?Miocene time. The stress regime within this graben changed from transtensional to transpressional. However, such reversal was not recorded in Tok Bidan Miocene sediments: the Dungun faults could have buffered the changes in stress during Miocene. The absence of wrench reversal in the Tok Bidan Graben indicated that Tok Bidan area could be stabilising during Miocene time. This Miocene reversal of wrench movement could be the manifestation of the changes in the stress regime within this portion of the basin. Changing stress direction is observed since Jura-Cretaceous. These changes could have resulted from the change of motion of the Pacific Plate and the progressive northward advancement of the Indo-Australian Plate during Miocene.