The Bonaparte Gulf Basin is a north-pitching syncline of Phanerozoic sediments, which are bounded to the south by Precambrian rocks and extend northward beneath the Timor Sea (Fig. 1). The landward part of the basin has been fragmented by faults, uplift, and erosion into a main outcrop area and three outliers. The eastern edge of the original depositional basin corresponds approximately with the present eastern margin, but the original extent to the south and west is unknown. Within the main outcrop is a Precambrian inlier, the Pincombe Inlier, which influenced deposition during the Upper Devonian and Lower Carboniferous. The main outcrop (Fig. 2) comprises Lower Cambrian volcanics, and Cambrian, Lower Ordovician, Upper Devonian, Carboniferous, Permian, Lower Triassic, and Lower Cretaceous sediments. The outliers contain only the lower part of this sequence, up to and including the lower part of the Upper Devonian.