Collision and Post-Collision Tectonics in Indonesia: Roles for Basin Formation and Petroleum Systems

Proceedings, Indonesian Petroleum Association
Thirty-Second Annual Convention & Exhibition, May 2008

Collision and Post-Collision Tectonics in Indonesia: Roles for Basin Formation and Petroleum Systems

Awang Harun Satyana*, Cipi Armandita*, Rudhy Laurel Tarigan**
* BPMIGAS
** PMU Petronas

Abstract
Collision occurs following subduction and accretion when two buoyant crustal masses collide. Collisional orogens result from collision. Shortly after collision, post-collisional tectonics occurs as tectonic compensation to collision. Isostatic gravity exhumation (uplift of once subducted continent), collapse of nearby basement, and lateral escape by strike-slip faults away from the collision zone are what represent post-collision tectonics. Collision and post-collision tectonics play significant roles for basin formation and the resultant petroleum system.

Collision and post-collision tectonics are elemental in Indonesia. We examined collisions in Indonesia which are important from the petroleum geology point of view: (1) Meratus, SE Kalimantan, (2) Buton and Banggai, Eastern Sulawesi, (3) Seram, (4) Timor-Tanimbar, (5) Lengguru, the Bird’s Head of Papua, and (6) Central Range of Papua.

In collision, the once subducted continent will eventually break off its oceanic slab due to its density and start to exhume and uplift its overlying collisional orogen. The uplift is isostatically re-adjusted by subsidence or collapse of the nearby basement and forms a post-collision sedimentary basin. The Neogene basins of the Barito, Buton, Banggai, Seram, Timor, Bintuni, Akimeugah, Iwur, and Meervlakte-Waipoga-Rombebai (North Irian Basins) were formed in this way. Continuing collision resulted in fold and thrust belts within the collided masses and its sedimentary basin migrating from the core of collisional orogen to the basin rim. This formed structural taps and multiple thrust sheets subsiding the basin’s source rocks. The maturation of source rocks were also by the burial of sediments of molassic deposits eroded from collisional orogen areas. Generated petroleum migrated to the available traps following the regional dip and lateral continuity of the carrier beds. Thick post-collisional molassic deposits may affect reservoir quality. Intensive deformation could risk the traps and complicate the migration routes.

Petroleum plays within collision areas are unique and need comprehensive understanding of collision and post-collision tectonic history. Proven petroleum accumulation in some collisional basins of Indonesia may provide references for other unproven collisional basins.

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