Abstract: Changes in Tectonic Stress Field in the Northern Sunda Shelf Basins

H. D. Tjia, K. K. Liew

The Tertiary hydrocarbon basins of northern Sunda Shelf are underlain by continental and attenuated continental crust characterized by moderate to high average geothermic gradients in excess of 5°C/100 m. In the Malay basin, Oligocene and younger sediments are more than 12 km thick. The smaller basins (which are commonly half grabens) and probably also the main Malay basin were developed as pull-apart depressions associated with regional north-to-northwest-striking wrench faults. Initial basin subsidence took place during the Oligocene, but at least one small basin may have developed as early as the Jurassic. Sense of movement of the regional wrench faults was reversed during mid- to late Miocene and in some of these faults, evidence was found for yet a younger phase of lateral d splacement. These offsets range up to 45 km right-laterally along north-trending fault zones. During most of the Cenozoic, succeeding wrench faulting with sense of movement in the opposite direction caused structural inversion of the basin-filling sediments, which became folded. The regional wrench faults act as domain boundaries, each tectonic domain being characterized by different stress fields. The evolving stress system can be attributed to varying degrees of interference of plate motions coupled with changes in movement directions and/or rates of the Pacific plate Indian Ocean-Australian

plate and possible expulsion of southeast Asian crustal slabs following the collision of the Indian subplate with the Eurasian plate.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994