In recent decades, researchers have identified an important and in some cases leading role of biological processes, primarily microbiota activity, in the formation of weathering crusts. The study of new features associated with crust formation is of both theoretical and practical interest. The aim of this work is to clarify the role of microbiota in the formation of the Mesozoic kaolinite-type weathering crust (exemplified by the Turgoyakskoye kaolin deposit) using microprobe analysis and electron microscopy. The research showed active involvement of diverse microbial communities in the formation of kaolin clays: scientists found various fossilized bacterial structures, including mineralized biofilms, pseudomorphs after coccoid and rod‑shaped bacteria, glycocalyx remnants, and filamentous microfossils. This microbiota is morphologically similar to bacterial forms described in laterites, but the biominerals composing them are fundamentally different. In kaolins, they consist of silicates and aluminosilicates, while in laterites they consist of Fe, Al, and Mn oxides and hydroxides, which indicates a different species composition of microbiota involved in the formation of lateritic and kaolinitic weathering crusts. These findings likely show that during weathering, climate controls not only chemical but also bacterial mineral formation. Unlike laterites, the distribution of microorganisms in kaolin clays is uneven – ranging from isolated remnants to mass accumulations. During kaolin formation, microbiota biomechanically destroys the matrix of the parent rock and simultaneously synthesizes new minerals, forming biomorphs from them. Among the latter, biomorphs after “titanium” bacteria are of particular interest. Their discovery confirms Academician V.I.Vernadskii’s view on the predominantly biogenic nature of titanium in rocks of mature weathering crusts.