Tectonics and Oil Prospects of the Moluccas, Eastern Indonesia

The greater Moluccas are bounded by th e Pacific and Indian oceanic plates and the greater Australian and Sunda continental crusta l plates or shelves. The effect of their opposing movement is a giant counterclockwise swor!' The island a rcs within this pattern are parts of subduction zones between the opposing plates. The Sorong transform left lateral fault resulted from these forces and offset remnants of the West Irian shelf terrane 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 T imor through Ce ram. Buru. and Sulawesi. T he age of emplacement of thi s zone in part is post-Lower Miocene pre-Middle Pliocene. Sedimentary rocks of pre-Pli ocene to Permi an age occur notably in Timor and th e Sula Islands. In most localities they are deformed and indurated to the extent of making them economic basement. Plio-P leistocene li near sed imentary basins follow the " S" trend and reach a maximum of 3.000 meters in thi ckness in northeast Ceram and Timor. Rocks include deep water claystones. shel f and lagoona l clays. bar and beach sands. and barrier coral reefs. Oil seeps occur on Ceram. Timor. a nd Buton (asphalt) mostly from Pli o Pleistocene rocks. Oil is produced at Bula. Ceram. from Plei stocene bar and shoreline sands in strat igraph ic traps. A recent development at Bula has established prolific production from an extremely permeable Pleistocene reef. The data suggest that oi l accumulation per unit volume of sediments is abnorm all y high in the Plio-Pleistocene. Reasonable extrapola tion indicates that major o il fields may be found in prospecting the "S" trend. Most likel y traps wi ll be stratigraphic with accumulations in beach. bar. a nd turbidite sands and reef limestones. Prospects a lso ex ist in other than Plio-Pleistocene in other portions of the Mo luccas. Prospecting for th ese subt le. elu s ive traps may be rewardin g if geologists exchange cer tain negative prejudices for a positive optimi sti c approach in combination with good ima gin at ive geology.