MAIN ASPECTS OF THE EPIGENESIS PROBLEM.

This paper presents the main trends in epigenetic research in the U.S.S.R. in the last. years: (1) Study of epigenetic zonality in thick series of sedimentary rocks of various ages and tectonic regions, (zones of unaltered clay matrix, of altered clay matrix, of quartizitic structures and hydromica-chloritic cement, and of prick-like structures and phyllite-like schists). (2) Principals of stadial analysis and mineral indicators of different epigenetic stages (clay minerals, organic matter, zeolites, feldspars, sulfides). (3) Facies of regional epigenesis connecting the main petrographic families or unaltered terrigenic rocks (quartz sandstones with kaolinitic matrix and the same composition of associated clays, acidic arkoses with hydromicaceous clays lithoclastic sands with several matrix components and associated clays, and volcanogenic greywackes) with ’related’ facies of regional metamorphism. (4) Some practical aspects of epigenesis are: for petroleum geology: maximum depth of burial according to porosity, interruption of quartz, feldspar, sphene, epidote, carbonate, biotite, and clay mineral epigenesis by oil migration; and for ore geology: (a) initial epigenesis: ore impregnation (e.g., volkonskoite of rock fragments; (b) deep epigenesis: e.g., galena impregnations due to release of trace elements during dissolution of rock forming minerals e.g., feldspars; and (c) metagenesis: ’Alpine’ veins across and along bedding, filled, e.g., with copper ores. [ABSTRACT FROM AUTHOR]