Abstract

The Banggai-Sula Microcontinent, located in the Provinces of Central Sulawesi and Maluku, is interpreted as being a fragment of the Australia - New Guinea Continent that became detached during late Mesozoic times. This is supported by similarities in the pre-Cretaceous stratigraphy resting on Paleozoic granitic and metamorphic basement. During the Middle Miocene to Pliocene the Microcontinent collided with the Asiatic PLate resulting in the eastward obduction of ophiolites in north-eastern Sulawesi.

Reconnaissance geological field mapping and sampling since 1983 has identified interesting Mesozoic outcrops on Peleng, Banggai, Taliabu and Mangole Islands. The sequence is dominated by an early Jurassic continental to shallow marine coarse clastic formation (Bobong) followed by deeper marine argillaceous facies (Buya). Late Cretaceous to Paleocene deep water carbonates (Tanamu Formation) represent the top of the sequence. Deposition is believed to have initially taken place within a rift-graben setting, followed by restricted shallow marine conditions and finally by subsidence and open, deep water marine conditions. Formations (Salodik/Pancoran) of Tertiary age follow unconformably and are dominated by shallow water platform carbonates.

Multichannel reflection seismic from the adjacent offshore areas also shows a well bedded Tertiary section resting unconformably on a thickly developed older interval, tentatively interpreted as being of Mesozoic age. A late stage Tertiary compressive episode, probably associated with the Sulawesi collision, has overprinted many of the older structural features.

Attractive reservoir objectives have been identified from outcrop samples within both the Jurassic Bobong Sand-stones and the Tertiary Salodik Limestones. Possible source rock potential exists within black anoxic Buya Shales and the early organic rich Salodik Carbonates. Organic maturities for the Mesozoic vary from post-mature (even for gas generation) in parts of Mangole, to immature for oil generation in Peleng and north-eastern Sulawesi. The Tertiary section everywhere remains immature at outcrop.

The generation and migration of hydrocarbons in the Banggai-Sula area appears to have taken place locally as indicated by the recent discovery of active surface gas (and possible oil) seepages.