Nomenclature for Sedimentary Rocks

Abstract

Despite the many excellent papers on classification of sedimentary rocks, there is still so much loose and variable usage of names that it is not possible to be certain of--or in some cases even to guess at--the intended meanings of terms found in the literature. This paper is presented to redraw attention to this confusion, to plead for wider employment of clearly defined terms, and to offer a general system of nomenclature which could provide greater uniformity and precision in terminology. This system is not revolutionary, but merely proposes restricted meaning for many current names and a general scheme for systematically deriving other names. The classical concept of sedimentary rocks as mixtures of mechanical and chemical fractions is the principal nomenclatural bas s in this system. The main name reflects the most abundant constituent of the dominant fraction. A finer division of silicate sandstone than customary is believed practical and desirable. Three terms are proposed to fill a conspicuous gap in terminology. Aggregal and integral describe textures of mechanical and chemical origin, respectively, but are defined petrographically. Accretic, a term correlative with clastic, describes aggregal textures composed of grains formed by accretion. The most important criterion for a nomenclature is that it must enable the reader to understand the terms employed by the writer. This understanding can be assured if the writer refers to an explicit classification or nomenclatural system.