The kinematics of extension and inversion in the Malay Basin, offshore Peninsular Malaysia

The evolution of the Malay Basin, a Tertiary extensional basin offshore Peninsular Malaysia, is explained in terms of a simple kinematic model that accounts for the following key observations: (1) Major basement faults along the basin axis are E-trending rather than NW-trending, (2) Through-going strike-slip faults are absent from the basin axis and margins, and (3) En echelon fold pattern in postrift strata seems to have been influenced by the geometry of underlying extensional half-grabens. Basin development during late Eocene-early Oligocene began with sinistral transtensional shear of a broad NW-trending shear zone (axial shear zone) which contains pre-existing E-trending basement faults. The shearing caused crustal blocks that are bounded by the faults to rotate anticlockwise and form E­ trending half-grabens between them. Reversal of shear during the early to middle Miocene, from sinistral to dextral, caused transpressive deformation and inversion of the half-grabens. The intensity of deformation increases southeastwards towards the West Natuna Basin as a result of the buttressing effect of the N atuna basement ridge which resisted the dextral motion along the axial shear zone.