The Oligocene gap in the formation of Co-rich ferromanganese crusts and sedimentation in the Pacific Ocean and the effects of bottom currents

The Marcus Wake and Magellan guyots formed about 129–74 Ma ago at 10°–30° S and drifted 1700–4400 km to their present-day latitudinal position across the equatorial zone of maximum deposition. Cooling of the Pacific plate brought these guyots to the northern arid zone during the Turonian–Maastrichtian, to depths at which sediment accumulation rates were low and the conditions promoted precipitation of Co-rich Fe–Mn crusts from the Campanian to the present. Nonprecipitation of Co-rich Fe–Mn crusts during the Oligocene was caused by the action of bottom currents. The presence of a hiatus identified in cores from drill holes was used as the basis for reconstruction of the directions of bottom currents in the Oligocene.