Marine Geology of the Southern Lord Howe Rise, Southwest Pacific

Abstract

In April 1972 Mobil Oil Corporation’s research vessel M/V FRED H. MOORE traversed several JOIDES Leg 21 drill sites on the southern Lord Howe Rise. The combination of these drilling results and Mobil’s high-quality seismic records provides important insights into the geology of this area. Neogene and Paleogene sedimentary thicknesses observed on our seismic records and derived from sonobuoy refraction measurements show a much greater degree of diversity than could be deduced from JOIDES data alone. Cenozoic thicknesses of about 3,000 m recorded in the New Caledonia Basin are most likely due to large-scale slumping from the flanks of the Lord Howe Rise and the Norfolk Ridge. Rapid sedimentary thickness changes from 0 to 1,300 m on top of the Lord Howe Rise are largely caused by a strong Neogene unconformity, beveling the highly block faulted Paleogene and older section. New seismic evidence strongly suggests the occurrence of continuous, explosive-type deep-water vulcanism throughout the Cenozoic. This region represents a margin between oceanic and “intermediate” crust (which in Late Cretaceous was at sea level).