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A revised lithostratigraphy is presented for the Finisterre, Sarawaget and Adelbert Mountains of northern Papua New Guinea, which form a thrust complex within the modern, broad, transpressive transform-fault system between the New Guinea Trench and the New Britain Trench. The region is underlain by the ?Eocene to Middle Miocene Wantoat Group (Finisterre Volcanics and Mebu Formation) and the conformably overlying reef carbonates and related sedimentary rocks of the Middle Miocene to Pleistocene Gowop Group. In the Finisterre and Sarawaget Mountains these units overthrust the continentally derived ?Eocene to Pliocene Mena Formation, the Pliocene Nariawang Formation and the Upper Miocene to Pliocene Ouba Formation, which was probably derived from uplift of the Papua New Guinea Highlands. There is a gradational relationship between the Ouba Formation and the upper part of the Gowop Group and a probable gradational relationship between the Ouba Formation and the Mena and Nariawang Formations. The Ouba Formation overlies the Wantoat Group unconformably, and the Mena Formationand the Finisterre Volcanics interdigitate. These lithostratigraphic relations demand a reappraisal of the interpretation of the Finisterre Volcanics as an allochthonous terrane, which collided with the Australian – Papua New Guinea craton in Pliocene times. The Finisterre Volcanics are most readily interpreted as having formed as an autochthonous plateau in the backarc basin or intra-arc rift-basin of the Sepik Arc t o the south which collided with Australia during the Oligocene.

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