MIXED-LAYER GLAUCONITE–NONTRONITE CLAY MINERALS FROM BIOMORPHOSES AND HOST ROCKS OF THE GZHEL STAGE MOSCOW REGION

During the study of the internal structure of the recently described new species of sponge Gzhelistella cornigera [Davydov et al., 2023] and fusulinids from the Gzhelian stage of the Moscow region, numerous polymineral biomorphoses were discovered, composed of mixed-layer clay minerals, goethite, chalcedony and sanidine. A detailed structural and crystallochemical study of clay minerals from biomorphoses and the host rock has revealed for the first time the structural heterogeneity of these mixed-layer minerals. Using the diffraction pattern modeling method, it has been established that the clay material in the studied samples is represented by two authigenic mixed-layer phases, glauconite-nontronite, with a contrasting relationship between different layers content and/or order in their alternation, but identical structural and crystallochemical characteristics of the crystallites. It has been shown that such formations should be considered as a single heterogeneous mixed-layer structure, in which the relationship and/or order in the alternation of different layer types in crystals vary within certain limits. It has been established that the structural and crystallochemical characteristics of mixed-layer minerals from brown biomorphs and from host rocks are almost indistinguishable, whereas for green biomorphs these parameters are significantly different. It is assumed that newly formed clay minerals from host rocks, like their brown analogs, were formed under similar physicochemical conditions. It is also obvious that during the formation of mixed-layer phases, brown biomorphoses were already deprived of biogenic organic matter, while green biomorphoses retained it in sufficient quantity to locally change the environmental conditions locally within themselves.