Geology and Paleontology of the Unique Mansurovo Locality of Early Triassic Tetrapods and Ichnofossils (Orenburg Region, Russia)

This paper discusses the geology of the unique Mansurovo tetrapod and trace fossil locality in the Orenburg Region of Russia (Gostevskaya Formation, Lower Olenekian Substage, Ustmylian Horizon). Sections of 16 trenches are described bed-by-bed and correlated throughout. Based on fossils (Wetlugasaurus malachovi grouping of the Wetlugasaurus Fauna) and lithology, the Mansurovo section correlates with the middle part of the stratotype section of the Gostevskaya Formation (Buzuluk Depression of the East European Platform). The site geology suggests that the four recognized geological members of the section were formed in a varying channel-floodplain environment during alternating depositional cycles. The depositional settings were reconstructed based on rock structure and texture and microlithological examination of thin sections. The tetrapod faunal assemblages, macrofloral remains and unique trace fossil assemblages are also studied. Based on the lithology and facies analysis, the depositional environment is reconstructed for the locality, showing the irregular riverine depositional pattern due to the wandering of river channels and their periodic drying out in a hot and semi-arid climate during the Early Olenekian. Taphonomy of fossil occurrences suggests that the burial took place in a riverine depositional environment affected by strong currents, and that the Temnospondyli probably died in subaquatic conditions.