Abstract

The Makassar Straits, located on the south-eastern margin of Sundaland, between the islands of Borneo and Sulawesi, is an under-explored deep-water domain, adjacent to a world class hydrocarbon province (Kutai Basin, primarily deltaic and shelfal).

Geological development of the Makassar Straits commenced during the Eocene in response to crustal extension that propagated south-westwards from the Celebes Sea spreading centre. After initial opening of the Makassar Straits, early-phase Eocene horst and graben terrains were overlain by basinal sag sediments during the subsequent Oligocene to Miocene era. Following uplift of Borneo during the Neogene and resultant massive outbuilding of the Mahakam Delta, considerable amounts of sediment were redeposited as turbidite facies in the North Makassar Basin.

During the Plio-Pleistocene, prior extensional settings in the Makassar Straits became compressional as successive fragments of micro-continental material, initially sourced from the Australian Plate ("Australoid"), collided with the south-eastern margin of Sundaland. This recent collision not only assembled the island of Sulawesi into its current (ephemeral) K-shape but also formed the West Sulawesi Fold Belt, which obscures the eastern part of the original Eocene rift in the Makassar Straits.

Traps within the foldbelt are mapped as compressional folds over a thin-skinned detachment within probably over-pressured, late Eocene to early Miocene mudrocks. Neogene turbidite reservoirs are postulated to be charged from both Paleogene and Neogene source rocks.