地球科学における粘土の意義(第25回記念粘土科学討論会特別講演集)

概要

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Significance of clay studies in the field of earth sciences has emerged from the merit of the clay-mineralogical viewpoint. As one point of view, the nature of clay minerals may be termed a wide variety (diversity) of crystallographic, mineralogic and chemical properties, and a variable behaviour (variability) being susceptible to the effects of physical and chemical attacks as evidenced by laboratory experiments. Clay mineralogists have learned that intergradient or mixed-1ayer minerals had specifically widely varying properties. Geologic field observations have provided a tremendous amount of available data on the mode of occurrence and distribution of clay minerals in various lithological types and geological age. On the basis of field and laboratory studies, clay minerals can be viewed as varied responses of rock material to particular geoscientific environmental conditions under which they were formed or altered, and likewise they will ultimately prove to be an important clue in unraveling the conditions. In the sequence proposed for the geologic events (such as hydrothermal alteration, weathering and diagenesis), the direction and cycle of changes in terms of materials and energy are visualized as illustrated by decreasing or increasing temperatures and pressures. and destructive or constructive processes of materials. Field observations and synthesis experiments lead to the belief that most intergradient or mixed-layer minerals can be viewed as hybrid silicate substances occurring in an intermediary stage of clay-mineral transformation, and thereby their formation may be an enough response to a continuously varying environmental condition as holding promise for applying to an indicator product of an environment which can be described in terms of the direction and cycle of changes. On the basis of the empirical laboratory data the condition of clay-mineral formation can be defined in physical-chemical terms. Geoscientists adapt the data to "an earth-size laboratory", and carry the geoscientific interpretations of argillization in the earth crust by reconstructing the geologic, petrologic and pedologic conditions in terms of physical-chemical parameters and likewise clay-mineralogical parameters. This review was written for the purpose of discussing the role of clay minerals in the field of earth sciences specifically in the light of the concept of intergradient and mixed-layer clay-minerals. Preparing this review, stimulation of thought comes often from the rccent trend of using several advanced chemical methods for clay, mineral studies as holding great promise for opening new aspects even in the field of earth sciences, and likewise from the old concepts such as the step rule and template principle, which merit renewed investigation and will help to put the present and future into perspective. In the final part of this review, the writer reported the study concerning the geologic interpretation of mixed-layer minerals in the sediments distributing in some oil fields of Japan. This work was done bringing together the knowledge of geology, crystallography and chemical kinetics. The discernible subsurface illite-montmorillonite mixing with an ordered interlayering is likely controlled by the factors such as geothermal gradients, rates of subsidence of sedimentasy basins, and certain stratigraphic horizons. The depth frequency of the first mixed-layer occurrence is likely in a statistically consistent relation to that of some organic geochemical parameters.
日本粘土学会の論文

著者

須藤俊男
日本粘土学会

地球科学における粘土の意義(第25回記念粘土科学討論会特別講演集)

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