Clay Sorting and Settling in the Ocean

Abstract

It is well known that shore and shallow marine sediments often contain few finegrained particles, even if clay minerals of natural or industrial origin are rarely totally absent from these environmeents (e.g., Griffin 1963, Stone and Siegel 1969). Except on muddy tidal flats and in some coastal depressions, clay particles are usually swept away, which was enhanced in late Quaternary periods by hydrodynamic variations linked to sea-level changes. The scarcity of the clay fraction in shallow water sediments, due to winnowing through the action of waves, tide, and currents, contrasts with the huge accumulation of argillaceous deposits in the rest of the oceanic range. A general grain size sorting therefore exists in marine basins between shore and offshore sediments, and one may wonder whether such a phenomenon affects the distribution of individual clay species. Early investigations already suggested the existence of clay sorting processes. Van Andel and Postma (1954) distinguished in the Gulf of Paria, Eastern South America, the delta platform characterized by dominant illite with associate kaolinite and smectite, and the other parts of the gulf somewhat enriched in smectite relatively to illite. Differential flocculation was considered as the most probable explanation among the four possible reasons discussed. Gorbunova (1962) observed in Indian Ocean sediments a decrease in kaolinite abundance with increased distance from India, and envisaged changes in conditions of marine transportation.