Abstract

A new model based on surface geology, seismic and well data is presented for the evolution of the Bone Basin. The basin, located between the south and southeast arms of Sulawesi, is interpreted to be a composite basin, with its origin as a subduction zone and suture between Sundaland and Gondwana-derived microcontinents, which subsequently evolved as a submerged "intramontane basin".

The Bone Basin began to develop in early Miocene time when eastern Sulawesi, a microcontinent derived from Australia, moved north-westward(?) and was partially subducted beneath western Sulawesi along the eastern margin of Sundaland.

A major collisional event occurred between east and west Sulawesi during the late Miocene time in Central Sulawesi and the intervening oceanic crust was obducted and overthrust eastwards onto eastern Sulawesi. The sedimentary package over the collision zone was folded and the carbonate build-ups in the northeastern part of the basin were tilted down to the west. In the southern part of the Bone Basin, westerly movement of eastern Sulawesi did not reach the collision stage with western Sulawesi. Instead, southeast Sulawesi was rotated eastward resulting in a major extensional fault cutting along the middle of the basin. The compression from the collision propagated a major back-thrust system westward to the subduction zone, generating foldbelts as indicated by the west-verging Kalosi and Majene foldbelts. The two colliding plates were locked up during the Pliocene and the continued plate convergence was accommodated by strike-slip movement along the Walanae, Palukoro and other faults.

A major erosional event in the Pliocene truncated the uplifted areas around the collision zone, while marginal marine and marine sedimentation continued within the basin. Clastic sediments from the surrounding mountains to the east, north and west were deposited progradationally southward toward the southern depocenter of the basin until present time.