BASIN TYPE ANALYSIS FOR SARAWAK BASIN

Controversies occur with the type of Sarawak Basin. Through analyzing the regional tectonic background, evolutionary stages, subsidence curves and reconstructing geological events, we acquire the following results: 1) The evolution of the basin can be divided into three phases: a) Subduction-accretion phase (Late Cretaceous-Late Eocene)—The Rajang oceanic crust subducted into Borneo base and formed volcanic island arc along the subducted edge ; b)Foreland basin phase (Oligocene-Early Miocene)—the collision between the Luconia plate and Borneo following the termination of oceanic crust subduction resulted to the development of peripheral foreland basin; c)Passive margin phase (Middle Miocene to present)—the opening of South China Sea, collision and uplift of Borneo leading to the stable subsidence of this basin. 2) Tectonic subsidence curves for the selected wells in Sarawak Basin resemble with the theoretical subsidence curves of a foreland basin—slow subsidence in early stage and rapid subsidence in later stage. 3)Reconstruction of geotectonic events for this basin reveals that in the late evolutionary stage, it is located at the passive margin setting. Based on the evidence mentioned above, it is concluded that the basin has experienced the process from peripheral foreland basin to passive continent margin basin.