The Oligocene Gap in the Formation of Co-rich Ferromanganese Crusts and Sedimentation in the Pacific Ocean and the Effects of Bottom Currents

摘要

The Marcus Wake and Magellan guyots formed about 129-74 Ma ago at 10 degrees-30 degrees 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-Maastrich-tian, 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.