Facies of regional epi- and metagenesis

Abstract

This paper discusses the gradational relationship of regional facies of sedimentary epigenesis (diagenesis) and of low grade metamorphism with particular emphasis on the arenaceous sediments. Formation of stable mineral assemblages representative of each facies is dependent upon the bulk composition of the original rock and the conditions under which changes take place. Rock families are classified into: 1) quartz-kaolinite; 2) lithoclastics; 3) acidic arkoses; 4) intermediate arkoses; 5) volcanic graywackes. processes of mineral transformation listed in order of increasing intensity are: a) early epigenesis;, b) deep (late) epigenesis; c) early metagenesis; d) late metagenesis. Each rock family develops a distinct mineral assemblage or facies during different stages of epigenesis and metagenesis. They are as follows: 1) quartz-kaolinite family — a) inherited composition, b) quartz-dickite, 9) quartz-pyrophyllite, d) cyanite; 2) lithoclastic family — a) inherited composition, b) chlorite-hydromica, c) muscovite-chlorite, d) epidote-muscovitechlorite-stilpnomelane, e) biotite; 3) acidic arkose family — a) vermiculite-femic relicts, b) quartzalbite-hydromica, c) muscovite-chlorite, d) epidote-muscovite-chlorite-stilpnomelane, e) biotite; 4) intermediate arkose family — a) vermiculite,femic relicts, b) laumontite, c) prehnite-muscovitechlorite, d) epidote-muscovite-chlorite-stilpnomelane, e) biotite; 5) volcanic graywacke family — a) heulandite-hydromica, b) laumontite, c) prehnite-muscovite-chlorite, d) epidote-muscovitechlorite-stilpnomelane, e) biotite. These are illustrated in tabular form and discussed in detail. Such facies are mappable on a regional scale. R. C. Epis