Abstract: Neogene Carbonate Exploration Play Concepts for Northern New Guinea: New Iteration from Field Work and Seismic Stratigraphy Along the Northern New Guinea Fault Zone
John D. Pigott, Carsten Geiger
Recent field reconnaissance, petrography, nanno and foraminifera age determinations, and seismic stratigraphy of the Sepik and Piore subbasins of northern New Guinea reveal the existence of an extensive, tectonically unstable, Miocene-Pliocene carbonate
shelf system. These findings represent the first recorded evidence of northern Papuan limestones coeval in age to those of the hydrocarbon productive Salawati Basin of Irian Jaya. Moreover, these observations also demonstrate the significance of episodic activities of the northern New Guinea fault zone upon the changes in carbonate sedimentation and diagenesis.
During the Neogene, algal biosparites (grainstones-packstones) to foraminiferal biomicrites (wackestones-mudstones) defined the clean portion of a mixed clastic-carbonate shelf system of the northern New Guinea basin, which began at the central New Guinea cordillera and deepened northward. This shelf was interrupted by coral-coralline algal boundstone fringing- to patch-reef buildups with associated skeletal grainstones. Clean carbonates were spatially and temporally restricted to basement blocks, which episodically underwent uplift while terrigenous diluted carbonates were more common in adjacently subsiding basement block bathymetric lows. These tectonic expressions were caused by the spatially transient nature of constraining bends of the evolving north New Guinea fault. As shown b seismic stratigraphy, by the late Miocene to the early Pliocene the uplift of the Bewani-Torricelli Mountains sagittally divided the shelf of the northern New Guinea basin into the Ramu-Sepik and the Piore basins. Continued regional sinistral transpression between the Pacific and the New Guinea leading edge of the Indo-Australian plates led to the reverse tilting of the Piore basin, the shallowing of the former distal shelf with concomitant extensive biolithite development (e.g., on subsiding volcanic islands), eventual uplifting of the Oenake Range, and en echelon faulting of the Bewani-Torricelli Mountains.
Hydrocarbon exploration play concepts developed from this study are sea level highstand algal grainstone-fringing reef boundstone belts, isolated patch-pinnacle reef boundstones, and tectonically fractured packstone-wackestones as reservoirs owing to vadose porosity creation during subsequent sea level lowstands. These carbonates would be sourced by hydrocarbons underlying pre-Neogene shales, which matured at geothermal gradients higher than those observed at present. Conduits for the near-vertical hydrocarbon migration were Pliocene and younger, transpressionally derived, down-to-basement faults.
AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994