ABSTRACT: Thick-Skinned, Basement-Involved Structures in the Western Part of the Papuan Fold and Thrust Belt, Papua New Guinea

VALENTI, GERARD L., Chevron Overseas Petroleum, Inc., San Ramon, CA

Recent hydrocarbon exploration activity has yielded new insights into the structural style of the western Papuan fold and thrust belt between Irian Jaya and ~142 degrees 30 minutes E longitude. Interpretation of surface mapping, remote sensing imagery, well data, and seismic data defines a structural style which, in contrast to the thin-skinned eastern Papuan foldbelt, is characterized by thick-skinned, basement-involved structures. The first order, 50 km-wide Muller Anticline dominates this area of the foldbelt and is proven to have basement involvement in at least the western two thirds of its extent by gravity data and by outcrops of granite of Permian age in the Strickland River gorge. Between the Blucher Range (142 degrees 15 minutes E longitude) and Irian Jaya, surface data sugg st that subsidiary structures to the Muller Anticline are also thick-skinned. Reflection seismic data over one such second order structure, Maipe Anticline, directly establish basement involvement and show fault displacement at depth terminating upward into anticlinal folding at shallower levels.

Using the seismically imaged Maipe feature as an analog, P'nyang Anticline, delineated only by remote sensing imagery and surface geology, was also interpreted as being a basement-involved compressional anticline. Subsequent drilling confirmed this interpretation by penetration of granodioritic basement rocks dated by K-Ar methods as being of Latest Triassic-Earliest Jurassic (205 + 5 my) age. The economic significance of these thick-skinned anticlinal structures has been established by recent drilling at P'nyang, where significant quantities of gas and condensate have been discovered in good reservoir quality sands within the Cretaceous Toro and Jurassic Imburu Formations.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)