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This paper is devoted to the X-ray diffraction study of bone fragments of Permian parareptile Deltavjatia vjatkensis obtained from the Kotelnich vertebrate fossil site, one of the richest of the Permian period, which is characterized by the excellent preservation of fossil remains because of their burial in a silty anaerobic environment similar to modern bogs. The bone is well-preserved and consists of fluorapatite, calcite, quartz, and dolomite. The refined apatite unit-cell parameters of a and b-axis (9.3526 ± 0.0001 and 9.3587 ± 0.0001) Å and c-axis (6.8930 ± 0.0001 and 6.8968 ± 0.0001) Å correspond to F-apatite. Crystallinity index determined as the full width at half maximum of the 002 reflection in degrees 2θ is 0.266–0.250, which is typical for Mesozoic vertebrate bones. Apatite crystallite size (length 70.3–74.9 nm, width 30.7–30.3 nm) in fossil pareiasaur bone is larger than in subfossil and recent mammal bone and is in a good agreement with the values for seismosaurus bone. Both crystallite size and aspect ratio (2.3–2.5) are independent of the fossil pareiasaur bone length.

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The study of the mineralogy and geochemistry of biomorphic ore formations has great importance for studying the processes of transformation of plant tissues during the formation of the sedimentary rocks, including ore mineralization. Forms of biogenic mineralization in sedimentary rocks are represented by various processes. The pyritization of organic residues is one of the most common forms. The purpose of this work was to conduct a detailed mineralogical and geochemical study of biomorphic ore formations collected from Mesozoic (Upper Jurassic) deposits of the right bank of the Volga river. The initial conditions for the fossilization of the objects of study were the same. Therefore, the structural and morphological features of the pyrite aggregate developing on them can be caused not only by geochemical conditions but also by the structure of the residues themselves. Samples were examined by optical microscopy, X-ray phase analysis, gamma-ray spectrometric analysis, X-ray computed tomography and X-ray fluorescence analysis. As a result of research, the stages of mineralization of wood were established, which reflect the features of sedimentation.

The Kotelnich pareiasaur site, one of the richest of the Permian period, is characterized by the unique integrity of fossil vertebrate assemblages and the preservation of bones’ internal structure (including fossil cellular structures) due to their burial features. Pareiasaur and suminia are two most widespread and most frequently encountered representatives of fossil fauna at the Kotelnich site, belonging to the herbivorous form of trophic affiliation. In the present work, a high degree of the structural preservation of the hard dental tissues of pareiasaur and suminia is demonstrated using scanning electron microscopy and energy dispersive X-ray spectroscopy. Fluorapatite composition of tooth tissues is indicated with trace rare earth elements and uranium incorporated from the host rock as a result of diagenetic alteration during fossilization. No secondary mineralization has been found in the pulp chamber uncovered by a cleavage. The features of its primary internal structure are observed such as pseudomorphs of iron-containing minerals over the fibrils of collagen fibers connecting odontoblastic processes with the walls of dentin tubules, as well as spherical pseudomorphs over blood-like cells.