RELATIONSHIP BETWEEN BATHYMETRY AND FERROMANGANESE DEPOSITS IN THE NORTH EQUATORIAL PACIFIC

Detailed surveys of the abyssal seafloor between the Clarion and Clipperton Fracture Zones have revealed a variety of bathymetric settings and a corresponding variety of ferromanganese nodule deposits. In the absence of large features such as seamounts, bathymetric settings are distinguished by their microtopographic character recognized on 12-kHz reflection profiles at scales of 0.5-sec sweep or less. Previous investigations have attributed the origin of microrelief on abyssal hills to contemporaneous sedimentation and tectonism (block faulting and extrusion volcanism) along minor structural trends. This survey found that rough areas, showing microrelief ranging from meters to tens of meters, contain generally higher coverages (kg/m2 of nodules that are more variable in bulk chemical composition and seafloor distribution than deposits in smooth bathymetric settings. Nodule distribution, however, is quite variable in all survey areas, with seafloor coverage typically varying by a factor of 2-5 × over distances of a kilometer or less. A volcanic influence to nodule distribution and chemistry is indicated by the narrow and somewhat lower Mn Fe range and moderate coverage (5.75 kg/m2) of a deposit located on an abyssal plain adjacent to several large seamounts. To explain these chemical and distributional trends, localized geologic processes that could regulate the exposure of basaltic rock, horizontal sediment redistribution, and hydrothermal activity are discussed in relation to nodule nucleation and growth along the sediment/seawater interface. © 1979.