Structure of Papuan Foldbelt, Emerging Hydrocarbon Province in Papua New Guinea

Kevin C. Hill

The 500-km long, northwest-southeast-trending, Mio-Pliocene foldbelt of west-central Papua New Guinea is part of an extensive 2,000-3,000-m high mountain belt through New Guinea that is similar in structural style to the Canadian Rockies. The southwesterly thrust-faulted sediments of the foldbelt are bound to the northeast by major sinistral wrench faults, with allochthonous metamorphic terranes to the north. The sedimentary section comprises 3-4 km of Mesozoic clastics, containing the main hydrocarbon reservoir, overlain by 1-1.5 km of Tertiary limestone.

The northeast two-thirds of the foldbelt has a Tertiary limestone duplex at surface and, by inference, Mesozoic duplex(es) beneath, with 70+ km of shortening. In the southwest foldbelt, there is considerable inversion of preexisting extensional faults and the limestone duplex is absent, implying deeper detachment. Shortening in the southwest was approximately 20 km.

Along strike, the foldbelt is divided into three segments by major regional lateral ramps. These ramps connect areas with different basal detachments, particularly in the southwest. The northwest segment decollement is 10-12 km into basement along the mid-crustal detachment. The resultant 200-km long Muller anticline exposes basement in the core and is prospective for hydrocarbons in the parasitic structures, such as the Juha gas-condensate field. The central segment prospective structures, such as the Mananda and Hides anticlines, are detached just above basement such that the entire sedimentary section is repeated. The southeast segment detachment is within the Mesozoic, but the structures, such as the Iagifu oil field, involve the sandstone reservoir and are prospective.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.