SUMMARY The paper presents the dynamics of the structural change of kaolinite and its polymorphous (polytype) modifications at different stages of sedimentary rock formation. Sedimentogenesis is characterized by a gradual disordering of structure of triclinic kaolinite, the degree of disorder produced being proportional to the intensity and duration of the influence of the hydrodynamic medium. Epigenesis (deep) is connected with gradual transformation of kaolinite into dickite through the stage of mixed‐layer growths inheriting the structure of twin rotations of disordered kaolinite from the sedimentogenesis stage. In metagenesis filling of fissures with dickite or nacrite takes place. The former is peculiar to the general thermodynamic medium of deep epigenesis/metagen‐esis, whereas nacrite is an indicator of intense stress and seems to be due to transformation of dickite.

SUMMARY This paper presents the main trends in epigenetic research in the U.S.S.R. in the last years: 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 quartzitic structures and hydromica‐chloritic cement, and of prick‐like structures and phyllite‐like schists). Principles of stadial analysis and mineral indicators of different epigenetic stages (clay minerals, organic matter, zeolites, feldspars, sulfides). Facies of regional epigenesis connecting the main petrographic families of 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. 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 in wood remains) due to intrastratal solution of heavy minerals and leaching 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.

For the purposes of this paper, the sediments have been grouped into "series" (Figure 2). The "series" do not necessarily correspond to "units" as defined by shipboard sediraentologists (see Site Report chapter, this volume). Also, the sediment terminology is that of the authors, and may not correspond to shipboard designations. Sample numbers are those assigned by the authors for the investigations.

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