Wacke, Graywacke and Matrix--What Approach to Immature Sandstone Classification? 论文

摘要

Huckenholz (1963) showed that the original arkose and graywacke overlap completely in both texture and composition; perhaps uppression ofone or both terms is indicated. Graywacke has the longer, if not more signif-icant (albeit confused), history. For 100 years in Germany and 50 in Britain, before development by Sorby of thin section petrography, graywacke was used as a purely hand specimen term based chiefly upon texture. It seems pointless to change this emphasis for an important, large, texturally-similar yet compositlonally-varied rock clan. Modal analysis and interpretation f immature sandstones presents many problems, especially that of matrix which is increasingly attacked as a classificatory parameter, chiefly of maturity. But it matters not how or when conspicuous matrix of graywackes formed for it to be useful for descriptive "coarse " separation ofpure (arenite) and impure (wacke) sandstones; genesis of fine material must be interpreted inany sand, recent or ancient. Finer subdivision can be made on a compositional basis following flexible schemes such as Gilbert's. Sedimentary struc-tures, tectonics, provenance, depositlonal process and environment should be avoided in petrographic classifica-tion. If textural and compositional maturity be accepted as the prime guides in classification, then purely quanti-tative placing of a rock within each maturity spectrum could replace all troublesome varietal names.