In the western Pacific, oceanic crust is Jurassic in age based on magnetic anomaly lineations. However, drilling expeditions have instead recovered mid-Cretaceous age basalts in deep, supposedly Jurassic age basins such as the Nauru, East Mariana, and Pigafetta. In the southern Nauru Basin, mulitchannel seismic reflection and sonobuoy refraction data support an off-ridge tectonic setting for the emplacement of mid-Cretaceous flood basalts over original Late Jurassic-Early Cretaceous oceanic crust. Forward modeling of refraction data provide velocity structure for coincident seismic reflection data to determine the types and thickness of materials overlying oceanic crust in the southern Nauru Basin. From these models the detection of thin, high velocity sills/flows within a thick, lower velocity layer are evident over a rough reflection surface interpreted as oceanic crust, with an age given by Mesozoic magnetic anomaly lineations. Oceanic crust clearly exists in the southernmost Nauru Basin without the overburden of high velocity sills/flows. Observations of thin sills/flows and oceanic crust beneath reflections from the mid-Cretaceous material cored at Deep Sea Drilling Project Site 462 indicate the presence of previously unsampled lithologic units in the Nauru Basin, notably oceanic crust
