The 62-mi (100 km) wide New Ireland basin extends north-westward from southwest of Bougainville to north of the Admiralty Islands. We have studied some 5,000 mi (8,000 km) of geophysical data from the basin north of Bougainville to west of Manus Island. The data were gathered by CCOP/SOPAC, the Australian Bureau of Mineral Resources, Gulf Oil Co., and a French Consortium.

The part of the New Ireland basin studied here is a fore-arc basin which contains Neogene sediments, and lies between two ridges formed as part of an old north-facing arc-trench system in the Oligocene and Miocene. The southern ridge is the old volcanic axis and consists of volcanic rocks forming New Ireland, New Hannover, and the Admiralty Islands. The northern ridge appears to be an accretionary prism which forms the southern flank of the West Melanesian Trench uplifted during its active phase in Oligocene-Miocene times.

The central New Ireland basin is generally a simple, little-deformed synclinal basin, with as much as 3 mi (5 km) of well stratified sediment along its axis. The basin fill contains several seismic discontinuities and unconformities and probably consists of Miocene-Pliocene-Quaternary volcaniclastic and carbonate sediments. The older sequences are lateral equivalents of sediments outcropping on New Ireland and other islands, but younger flat-lying carbonate oozes and turbidites are ponded in the basin. North of New Ireland a number of volcanic islands consisting largely of pyroclastic rocks and lavas have cut through the basin.

Northeast of Manus Island, folding and faulting in the basin increase markedly, with faults forming large scarps on the sea floor. Volcanism may have had a more active role in sedimentation, reducing seismic penetration in the sediments in areas of extensive flows. North of Manus Island, young deformation and volcanism have replaced the flat-lying strata common to the central basins area, obliterating further traces of the deeper basin, if it exists.

The thickness of the sedimentary sequence, and the possible presence of some carbonate buildups at depth in the central basin, indicates that the basin may have some petroleum potential. Major unknowns are source rock potential, and the thermal gradient history in the basin. Carbonate buildups are the most likely reservoir rocks for any petroleum generated in the basin.

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