The outcrop of the Middle Ordovician (Darriwilian stage) and Upper Devonian (Frasnian stage) Yakhnovo as a unique geological feature in the East of the Main Devonian Field

At present, within the Baltic-Ladoga structural-facies zone characterized by the distribution of coastal-marine and coastal-continental deposits of the Lower and Middle Frasnian outcrops of bedrock are practically lost. In the Yakhnovo outcrop, rocks of the Volkhov Formation (Darriwilian), as well as the Vazhinskaya and Syasinskaya Formations (Lower Frasnian) are exposed. The rocks of the Volkhov Formation contain a complex of soft-bottom ichnofossils with the dominant ichnogenus Thalassinoides Ehrenberg, characteristic of the sublittoral environment above the base of storm waves and below the base of normal waves, as well as a hardground surface with characteristic traces of Trypanites Mägdefrau drilling. Traces of Arenicolites Salter, occurring in deposits of highly dynamic shallow water zones, have been established in the rocks of the Syasinskaya Formation; a large arthropod trace was found in limestone blocks in the talus, presumably belonging to the ichnogenus Rusophycus Hall, considered as a domihnia (burrow) of arthropods. Findings of large arthropods have not previously been recorded in the Frasnian rocks of the eastern Main Devonian Field. The study has proved the historical, stratigraphic, ichnological, paleoecological, paleogeographic value of the Yakhnovo section, which is actually the only outcrop demonstrating the features of the carbonate-terrigenous section of the lower Frasnian, formed in the shallowest zone of the early Frasnian Sea.