On the origin of Ethmodiscus ooze

Abstract

Ethmodiscus ooze is essentially a monospecific diatomaceous deposit found in the equatorial parts of the oceans. Laboratory dissolution experiments on fossil diatom assemblages from the deep-sea floor show that Ethmodiscus rex is very resistant to dissolution. This species is therefore concentrated in the diatom assemblages subjected to experimentally controlled dissolution in seawater. Examination of deep-sea sediments, labelled in the literature as E. rex oozes, indicates that two different types of sediments are involved. In the first type the entire siliceous assemblage is made up by Ethmodiscus fragments. The second type is numerically dominated by Ethmodiscus fragments but includes an amount of etched, dissolution-resistant species. It is suggested that the first type of Ethmodiscus ooze is formed by a combination of differential dissolution and winnowing, whereas the second is created by differential dissolution.