Seismic, borehole, and field data acquired over the last 12 years demonstrate that the structural style in the Papuan Fold Belt comprises inverted basement extensional faults and asymmetric detachment folds that break through the overturned forelimb. The previous fault-bend fold model was flawed because of a lack of data and because of inappropriate analogs that ignored the mechanical stratigraphy.

In the oil province of Papua New Guinea, the deformation front has not yet impinged on strong Australian lithosphere, so a relatively low fold belt occupies its own foreland basin. The adjacent gas-condensate province in the western Papuan Fold Belt has just impinged on the strong lithosphere, developing a foreland basin and basement-cored anticlines. Along strike in the Irian Jaya Fold Belt, the deformation front has encountered the buttress of the strong Australian lithosphere, causing a 15-km-thick Paleozoic and Mesozoic sequence to be thrust to the surface along a previously extensional, basin-margin fault. Focusing deformation on one fault has created mountains 5 km high and an adjacent foreland basin. Structures in the mountains are breached, but the adjacent foreland basin has hydrocarbon potential. Farther west, in the “Bird's Neck” area, the poorly known Lengguru Fold Belt resembles the oil province in the Papuan Fold Belt, but Pleistocene extensional faulting may have caused breaching. In addition, deep burial by thick Tertiary carbonates has probably destroyed reservoir porosity, except in the north, where additional discoveries like the 30-tcf Tangguh gas province are possible.