The Central Range of Irian Jaya is expressed by fold belt with dominantly south or southwest directed thrusting. This fold belt represent a suture zone between the Pacific Oceanic Plate in the north and the Australian Continental Plate in the south. Most of the area consist of Australian Continental Margin sediment. Structures in the Central Range reflect thrusting from the north or northeast, asymmetrical anticlines, with thrust faults and narrow steep south flanks. Most of the anticlinal axes and associated thrust faults trend is WNW-ESE. The Central Range is formed by over 6000 meters of platform sediments. The sediments are predominantly arenaceous and argillaceous rocks of Paleozoic to Mesozoic age overlain by the Tertiary New Guinea Limestone Group. The oldest rock is the Pre Cambrian low metamorphic elastic. A similar geology of the Central Range is the fold belt of Papua New Guinea. Landsat imagery shows several WNW-ESE trending surface anticlines in the western part of this area. These structures at the surface are up to 5 km wide and 15-20 km long,very similar to the productive structure in Papua New Guinea, where numerous oil seeps , oil and gas are discovered in the Late Jurassic and Early Cretaceous sandstones in the frontal thrust zone. Data obtained from recent geological surveys have furthermore increased the knowledge concern-ing the geological aspects of this area. A good potential hydrocarbon source rock sediment was recorded in Mesozoic shales of Kopai and Piniya formations and Paleozoic shales of Aiduna Formation. Four potential reservoir formations are present. They are sandstone in Tipuma, Woniwogi and Ekmai forma-tions with limestone in New Guinea Group. Hydrocarbon indications have been proven in the Central Range area as oil seeps and oil stained at Tiom, Wamena, Magi and Oro.
Authors : Dudu Masduki & Harry Sugiharto