Geochemistry of Epigenesis

In its classical sense "epigenesis" refers to all geological processes originating at or near the surface of the earth. It thus embraces all those phenomena which we associate with the land scape; Perel'man has already written extensively on this subject. The landscape, in the physical sense, is controlled by the interac tion of exogenic and endogenic agencies-on the one hand, the atmo sphere, the wind, the rain, and other components of the weather, the forces of running water and the planetary controls of gravitational and tidal nature; and on the other hand the materials of the earth's crust, from sediments to metamorphic rocks and igneous materials from deep endogenic sources. In practical terms the epigene region involves the products of weathering, the soils, the transported material, the colluvium of hillsides, and the alluvium of stream valleys. It involves those landforms that are products of the erosional sculpturing of the landscape, as well as those that result from accumulation, such as glacial moraines and desert sand dunes. The science of geomor phology is gradually beginning to evolve from a passive cataloging of scenery and its deduced causes (in the Davisian sense) into a vigorous study of dynamic processes. These are partly geophysical, in the sense of hydraulics and mechanical studies, and partly geo chemical.

Texte du rabat

In its classical sense "epigenesis" refers to all geological processes originating at or near the surface of the earth. It thus embraces all those phenomena which we associate with the land­ scape; Perel'man has already written extensively on this subject. The landscape, in the physical sense, is controlled by the interac­ tion of exogenic and endogenic agencies-on the one hand, the atmo­ sphere, the wind, the rain, and other components of the weather, the forces of running water and the planetary controls of gravitational and tidal nature; and on the other hand the materials of the earth's crust, from sediments to metamorphic rocks and igneous materials from deep endogenic sources. In practical terms the epigene region involves the products of weathering, the soils, the transported material, the colluvium of hillsides, and the alluvium of stream valleys. It involves those landforms that are products of the erosional sculpturing of the landscape, as well as those that result from accumulation, such as glacial moraines and desert sand dunes. The science of geomor­ phology is gradually beginning to evolve from a passive cataloging of scenery and its deduced causes (in the Davisian sense) into a vigorous study of dynamic processes. These are partly geophysical, in the sense of hydraulics and mechanical studies, and partly geo­ chemical.

Contenu

1. Geochemical Role of Living Matter (Biogenic Migration).- Formation of Living Matter.- Decomposition of Organic Matter.- Biologic Cycle of Chemical Elements.- Living Matter in Geologic History.- 2. Geochemical Parameters of Elements Which Condition Their Physical and Chemical Migration.- Chemical Bonds and Crystal Lattices of Minerals.- Valence.- Dimensions of Ions and Atoms.- Isomorphism.- Ionic Potential.- Solubility.- 3. Law of Mass Action in Geochemistry.- Dissociation Constant and pH of Water.- Dissociation Constants of Acids.- Complex Ions.- Undissociated Molecules.- Solubility Product.- Ionization Power of Natural Waters.- Concentration of Elements in Natural Waters and Its Significance to the Formation of Minerals.- 4. Analysis of Energy Involved in Supergene Migration.- Chemical Affinity.- OxidationReduction Reactions.- Electrochemical Leaching of Sulfide Ores.- Stability Ranges of Minerals and Chemical Compounds.- LeChatelier Principle.- Fersman's Geoenergetic Theory.- Principle of Retardation of Reactions.- 5. Migration of Colloids.- Occurrence of Colloids in the Supergene Zone.- Migration of Substances in the Colloidal State.- Sorption.- Principal Groups of Colloidal Minerals.- 6. Occurrence of Chemical Elements in the Supergene Zone.- 7. Natural Media of the Supergene Zone.- Soil.- Weathered Crust.- Surface and Ground Waters.- Geochemical Landscapes.- Water-Bearing Strata of the Catagenetic Subzone.- Weathering and Cementation.- Epigenetic Zoning.- 8. Factors in the Development of Media in the Supergene Zone.- Climate.- Zoning.- Geologic Structure.- 9. Classification of the Epigenetic Processes Operating in the Supergene Zone.- Typomorphic Elements.- Aeolean and Aqueous Migrants.- Intensity of Aqueous Migration of Chemical Elements.- Classificationof the Supergene Processes.- 10. Epigenetic Processes of Oxidation.- The Sulfatic Processes.- Acid Processes.- The Neutral Carbonatic Process.- The Chlor-Sulfatic Process.- The Soda Process.- 11. The Gley Processes of Reduction in Epigenesis.- 12. Epigenetic Processes in Reducing, Sulfidic Environments.- The SulfatoSulfidic Process.- The OxysaltSulfidic Process.- The SodaHydrogen Sulfide Process.- 13. Geochemical Barriers.- The Principal Types of Geochemical Barriers.- Epigenetic Concentration of Elements During Cementation (Approximate Calculations).- 14. Development of Epigenetic Processes Through Geologic History.- 15. Conclusions.- The Uniqueness of Migration.- Geochemical Types of Epigenetic Processes in Natural Media of the Supergene Zone.- The Geochemical Classification of the Natural Media in the Supergene Zone.- The Criteria for the Recognition of Epigenetic Processes.- The Geochemical Types of Reducing Environments.- The Geochemical Classification of Natural Waters.- Vertical Hydrochemical Zoning in Ground Waters.- Supergene and Hydrothermal Processes.- Formation of Mineral Deposits Surrounded by Secondary Dispersion Haloes.- Methods of Studying Epigenetic Processes.