Subsidence nature of a strike-slip related basin: an example learned from the Sarawak Basin

Abstract

The subsidence nature of a strike-slip related basin is the least Wlderstood as compared to the rift basin and the basin formed by the lithospheric flexure which is al~o ~owr:t ~ a foreland basin. In brief, the rift basin of McKenzie model has a subsidence profile w~h is characterised by fast initial subsidence and followed by a slower thermal subsidence. In contrast, th,~ forelapd basin is charactensed by a slower initial subsidence and followed by rapid subsidence to the en4 of basin formation. The subsidence profile ofSarawak Basin was selected for this discWJs~on ,as the seismic interpretations concluded that the basin was formed by strike-slip tectonism, contra4ictmg ~ a foreland basin in terms of its tectonic origin; i.e. it was created by lithospheric flexure by th~ ~w>ducijon of South China Sea oceanic crust beneath the NW Sarawak continental crust. The study has been conducted using commercial software, Basin Modelling System Version 4 by Platte River Associates. The result of the study shows that the burial hjstory curves for the wells representative of the Sarawak Basin show many of the profiles with e,ai-Jy r~pid subsidence fonowed by a later phase where basement subsidence is slower, indicative of rifted style qftectonic origin. These are followed either by a series of later compressional basin inversion or cpntinued with thermal subsidence similar to a rift basin profile. The evaluation of stretching factors and heat-flow shows a direct reJati.onship through out the basin which are consistent with the origin of a basin dominated by strike-slip ~ctonics. The finding of this study helps in understanding the nature of subsidence in the strike-slip r:el~~e,~ ,b~in which concurrently challenges earlier models for a subduction-related origin for the S~awak Basin.