Abstract

The greater Moluccas are bounded by the Pacific and Indian Oceanic plates and the greater Australian and Sunda continental crustal plates or shelves. The effect of their opposing movement is a giant counterclockwise sworl. The island arcs within this pattern include parts of subduction zones between the opposing plates. The Sorong transform, left lateral fault resulted from these forces, and remnants of the Irian Jaya shelf terrain are offset at least 700 kilometers westerly to the Sula Islands. Fossil subduction zones are present in the form of melanges, including a persistent zone extending in an “S” pattern from Timor through Ceram, Buru, and Sulawesi. The age of emplacement of this zone in part is post-Lower Miocene to pre-Middle Pliocene.

Sedimentary rocks of Miocene to Permian age occur notably in Timor and the Sula Islands. In most localities, they are deformed and indurated to the extent of making them economic basement. Plio-Pleistocene linear sedimentary basins follow the “S” trend and reach a maximum of 3000 meters in thickness in northeast Ceram and Timor. Rocks include deep water claystones, shelf and lagoonal clays, bar and beach sands, and barrier coral reefs.

Oil seeps occur on Ceram, Timor, and Buton (asphalt), mostly from Plio-Pleistocene rocks. Oil is produced at Bula, Ceram, from Pleistocene bar and shoreline sands in stratigraphic traps. A recent development at Bula is prolific production from an extremely permeable Pleistocene coral reef.

The data suggest that oil accumulation per unit volume of sediments is abnormally high in the Plio-Pleistocene. Reasonable extrapolation indicates that major oil fields may be found in prospecting the “S” trend. Most likely traps will be stratigraphic with accumulations in beach, bar and reef limestones, and possibly turbidite sands. Prospects also exist in other than Plio-Pleistocene in other portions of the Moluccas. Prospecting for these subtle, elusive traps may be rewarding, if geologists exchange certain negative prejudices for a positive optimistic approach in combination with good imaginative geology.