The Place of Clays in the Geochemical Cycle

Abstract

The reconstruction of the path and the behavior of chemical elements in the course of evolution of the earth's crust is fascinating work. The ``geochemical cycle'' is the evolutionary succession that occurs during the following stages: weathering, transportation, sedimentation, diagenesis, metamorphism, and genesis of crystalline rocks. Clays belong within the first four stages of this cycle, these being surficial stages. In fact, after that, they are transformed by metamorphism and granitization. Clays have thus a birth and a death, or better, several births and deaths during the geochemical cycle. In order to situate correctly the place of these births and the place of clays in the succession of events, it is necessary to study the main geochemical characteristics of sedimentary rock series. This study will be subdivided as follows:I.Geochemistry of normal sedimentary series.II.Geodynamic interpretation of this series.III.The positive and negative sedimentary sequences.IV.The evolutionary series of pedological origin.V.Confrontation and general view on sedimentary series.VI.The place of clays in the surficial part of the geochemical cycle.