The western Woodlark Basin is one of the best areas to study the processes of rifting as a precursor to seafloor spreading. It is one of the few areas of the world where a very strong case can be made for rifting related to large-scale simple shear on a relatively low-angle (~30°) extensional detachment fault (Taylor et al., 1995). Extension was achieved by westward propagation of a spreading center into the previously rifted continental crust of Papua New Guinea (Benes et al., 1994; Taylor et al., 1999). A preexisting subduction-related arc, the Miocene Trobriand arc, was rifted at ~6-8 Ma to form the Pliocene-Pleistocene western Woodlark rift basin, adjacent to Papua New Guinea (Weissel et al., 1982; Taylor et al., 1999). Here, we refer to the Woodlark Basin as the entire sedimentary system associated with the western Woodlark Basin, including the uplifted footwall to the south forming the Moresby Seamount, the deep rift basin, and the downflexed rift margin further north (Fig. F3).
Interpretation of sediment provenance within the Woodlark Basin must take into account a complicated regional tectonic setting (Davies et al., 1987; Honza et al., 1987; Lock et al., 1987). During Neogene time, calc-alkaline volcanoes were active within an arc that was mainly located to the south of the present Woodlark Basin in Papua New Guinea (Smith, 1982; Smith and Milsom, 1984). However, similar calc-alkaline volcanoes were located further north within the present forearc region (e.g., Woodlark Island) (Ashley and Flood, 1981). Papua New Guinea, an obvious potential source of terrigenous sediment in the Woodlark Basin, is geologically complex and includes Neogene arc volcanics, a Paleogene ophiolite, and underlying metamorphic rocks (Davies and Jaques, 1984).