Annotated record of the detailed examination of Mn deposits from DSDP Site 65, Leg 7 (Cores 65-7, 65-9, 65-14, 65-17, 65A-1)

An acoustically very transparent layer is present over much of the deep basin—here termed the Central Basin—between the Gilbert and Marshall Islands on the west and the Line Islands on the east. The Pacific Panel recommended drilling in this region to sample at least the upper transparent layer, and the first opaque layer beneath. Several possible sites were considered by the panel and by the shipboard party. Of paramount importance in choosing a particular site was a concern that sufficient sediments be present to bury the bottom-hole assembly (the drill collars and bumper subs) before the bit struck hard rock. A set of nearly continuous cores of an apparently uninterrupted section of radiolarian ooze ranging in age from middle Eocene to Recent was obtained, but the bit did not reach the deepest seismic reflector. Below depths of 127 meters, in the Oligocene and Eocene, thin chert and turbidite beds are sparsely interbedded with ooze.