The Tectonostratigraphic Evolution and Tertiary Petroleum Systems of SE Asia - An Updated Model

Longley, Ian M.
Exploration, GIS-Pax, Perth, WA, Australia.

SE Asia is covered by numerous Tertiary Basins. The formation of these basins on the Sundaland pre-Tertiary promontory was triggered by an Middle Eocene global plate re-organisation at 50Ma. The regorganisation caused a slow down of subduction rates and arc parallel extension in the backarc portion of the Sunda Arc that formed the southwestern and southern boundaries to Sundaland. The rest of Sundaland experienced a phase of regional extension where two sequential rift systems propagated westwards from the "open" Pacific margin. The first formed Makassar Straits and the second opened the South China Sea. The drift blocks in the SCS eventually choked and extinguished subduction beneath the NW Borneo subduction system in the middle Miocene uplifting the hinterland of Borneo triggering erosion and the deposition of sediments into the proto-Baram and Kutei/Mahakam deltas.

In the Sunda backarc basin areas the post-Eocene evolution comprises a second slowdown of subduction rates caused by the "Hard Collision" of India into Eurasia in the middle Oligocene (~35Ma) which caused a widespread subsidence phase. Subsequently the progressive clockwise rotation of Sumatra caused inversions, the Great Sumatra Fault to form and eventually the opening of the Andaman Sea.

In the Indo-China area the onset of hard collision caused two sequential extrusion fault systems to develop. The first linked dextral extrusion fault movements through onshore Thailand forming extensional basins at releasing bends and extending down through the Gulf of Thailand, Malay and West Natuna areas where the older Eocene rifts were overprinted. The second extrusion exploited the Red River Fault suture forming the Yinggihai rhombochasm.

In the east blocks sliced from the northward moving Australian plate were transported eastwards and eventually collided with the eastern edge of the Sundaland area in the middle and late Miocene. These collisions formed Sulawesi and established through going wrench systems that linked across northern Borneo to form a foldbelt in the northern Baram Delta area.

This tectonic evolution model detailed via a set of tectonic reconstruction sketches and paleogeographic maps explains the origin, fill and inversion of the major basins of SE Asia and when integrated with an understanding of the source rocks in the basins it can explain relative richness/endowment and phase mix (oil vs gas nature) of all the basins.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012