Vendian Paleosol of Gubakha (Perm Krai, Russia) As a New Example of the Interaction of Terrestrial Biota and Substrate at Near-Sea Lowlands in the Late Proterozoic

The paper focuses on a preliminary description of a paleosol profile (microprofile) of Late Proterozoic (Vendian) age. The profile was found on the left bank of the Kosva River downstream of the Shirokovsky water reservoir (Gubakha raion of Perm krai). The upper part of this profile (genetic horizons of B and BC) is dissected by vertical cracks of desiccation. The lower part of the profile (siltstone of the horizon C) contains fossils of soft-bodied metazoan organisms, including pinnate forms (Petalonamae), bilateral movable benthic forms (Proarticulata), medusoids, and cyanophyte-bacterial films. A distribution model for the studied facies and paleoecological habitats is proposed. The paleosuccession is reconstructed on the basis of the sections studied and discussed. The matrix containing the paleosol profile formed under conditions of a near-coast shallow-water basin. The siltstones of the matrix with a lumpy structure and small spherical concretions were exposed to aerial conditions, which influenced the structure of the initial sediment from a stratificated layer to a lumpy soil matrix as a result of vertical cracking of the initial sandy-clayey matrix. After that, the conditions of shallow-water marine or lagoon basin returned, and the biota of soft-bodied organisms developed there. Then, after the shallowing of the basin, the deposited sediments were exposed to aerial conditions again, perhaps in a wave-breaking zone near the littoral. The presence of water allowed the bacterial-algal community to develop. Atmospheric agents together with insolation led to cracking of the upper surface of the forming soil microprofile FPS-Sh1.