Abstract

The various structures in the West Natuna Basin were formed deformation during two distinct deformation periods. The first phase was one of crustal extension, lasting from 40-29 m.y., which resulted in graben development in the Boundary area. The second phase was dominated by compression, and this resulted in basin inversion (in two stages) and a population of geometrically consistent structures. The compressional phase commenced about 29m.y., with the onset of left-lateral wrench movement, and after a priod of quiescence from 20-15 m.y., right-lateral movement occurred until about 10 m.y. by which time most of the compressive structures were formed. These NE-SW anticlines are important oil-bearing structures in the West Natuna Basin. The two deformation types are interpreted to be the result of the collision of India with Eurasia, and the consequent extrusion and clockwise rotation of Indo-china-Sunda. Pre-collision reconstruction of Eurasia suggests that an extensive Jurassic suture, separating Indochina and Sunda, was responsible for allowing the propagation of the Malay-Natuna-Lupar shear zone, and consequently this facilitated basin development in the area.