Mineralogy, geochemistry, and origin of Pacific red clays: A review

Abstract

Abstract Pacific red clays are dominantly allogenic in origin. The allogenic component is derived principally from aeolian dust from central Asia, Australia, and Central America. The highest input of dust is from central Asia. Sedimentation rates of red clays are therefore higher in the North Pacific than in the South Pacific. Being composite in origin, the allogenic fraction of red clays is similar in composition to that of shales. However, this does not necessarily imply a genetic origin of red clays from shales. Sedimentation of red clays is variable through time. The highest rates of allogenic sedimentation were during glacial periods when aeolian dust transport was a maximum. Red clays are found in oxic pelagic environments where reduction of nitrate by organic carbon in the pore waters does not occur. This permits oxidation of Mn and Fe to their higher valencies with the consequent adsorption of certain transition elements on their oxides. This situation corresponds to sedimentation rates of <40 mm/...