Diagenesis in Clay Minerals—A Review

Abstract Diagenesis refers to the process, and the changes (usually excluding cation exchange) that take place in sediments after deposition, but definitions of the process vary widely over which changes, and what part (or all) of the time between the transportation of the sediment and the time that the sediment(ary rock) is studied, should be included in diagenesis. Furthermore, Weaver, Griffin, and others, have favored alternative explanations to account for many clay mineral distributions that previously have been interpreted as representing changes in clay minerals in both recent and ancient sediments, and which were referred to diagenesis. Although agreeing that such alternative explanations account best for many distributions of clay minerals, additional evidence that presumably is convincing of diagenesis is presented herein to account for the formation of certain other occurrences of glauconitic mica, glauconite, illite, corrensite, kaolinite, and vanadiferous micaceous clay. A two-stage mechanism is proposed for a possible process by which illite and probably corrensite are formed: (1) cation sorption driven by energy (activities) of the ions in solution, and binding energy of the clay minerals, and (2) subsequent rearrangement of ions in the clay mineral to produce illite. It is finally proposed that diagenesis of clay minerals is characterized by the addition to and incorporation into them of Me ions, such as Mg, K, Ca, Na, Al, Fe, V, SiO 2 , and others, driven mainly by chemical energy and aided by mechanical and thermal energy, but as the latter two become more effective the process is designated metamorphism (anamorphism). Long-time, diagenetic reactions after burial of sediments are probably less important, volume-wise, than provenance and terrestrial weathering in determining the mineralogy of argillaceous sedimentary rocks in the geologic column.