Abstract—: The complex mineralogical–geochemical and isotope–geochronological study of globular phyllosilicates (GPS) of glauconite–illite series from Upper Proterozoic deposits of the Olenek Uplift (North Siberia) was performed. The Rb–Sr and K–Ar dates of the post-diagenetic transformation stages of GPS from the Osorkhayata and Arymass formations of the Solooly series were obtained. These dates along with the model cation distribution in the structure of minerals and comparison of the model results with the Mössbauer and IR spectroscopic data give grounds to assume that the post-diagenetic transformation of crystalline structure of GPS and their chemical and isotope compositions occurred during the Pre-Debengda hiatus (1280–1250 Ma).