Abstract

Sequence analysis using reflection seismic integrated with borehole data documents the evolution of the Northern New Guinea Basin. The data reveal the Piore and Sepik Basins, two present-day sub-basins of the Northern New Guinea Basin, to have been depositionally contiguous during the Miocene. Both sub-basins are floored by a complex Paleogene basement assemblage that includes fragments of a volcanic arc and sporadic occurrences of Bliri Sequence sediments. The overlying Miocene Sepik Sequence baselaps and consists of shallow marine to pelagic carbonates and axially transported slope systems which thin northward. A Late Miocene relative fall in sea level is recorded by a basin-wide unconformity. The subsequent Pliocene uplift of the Bewani-Torricelli Mountains along the active Northern New Guinea Fault System sagitally separated the two basins, segmenting the North New Guinea Basin into the Sepik Basin to the south and the Piore Basin to the north. The segmentation is recorded within the Wewak Sequence sediments, as a Bewani unconformity.

The post Bewani unconformity Piore Basin experienced north to south tilting toward the Bewani-Torricelli Range, accelerated subsidence in the south, and gradual uplift in the north culminating in the Quaternary emergence of the Oenake Range. Northward prograding fluvial-deltaic systems initiating from the Bewani-Torricelli Mountains deposited the Wosera Sequence within the Piore Basin. In comparison, the Sepik Basin experienced a southward tilting away from the Bewani-Torricelli Mountains with the Wosera Sequence sediments recording west to east prograding systems which vertically grade from marine slope to deltaic to fluvial depositional environments. Proximal to the Northern New Guinea Fault Systems, both basins are overprinted by a variety of wrench fault style structures. The resulting basement-penetrating faults may afford potential hydrocarbon pathways from depth for the observed surface oil seeps, among apparent thermally immature source rocks.