About the Age of Fossil Flora of the Kygyltasian Regional Stage of the Upper Paleozoic in the Verkhoyansk Region, Northeastern Russia

The Kygyltasian Regional Stage is widespread throughout the Verkhoyansk Region, where it reflects a large transgressive-regressive cycle of the Verkhoyanian terrigenous sedimentation. Over the years, a huge amount of material has been accumulated on biostratigraphic division, facies features, and paleontological characteristics of this large stratigraphic unit, but its age is still debatable. The main fossils in the upper part of the Kygyltasian Regional Stage are higher plants, the remains of which were studied in the last century using outdated taxonomy. This study is devoted to revision of the collection of fossil plants from the type locality of the Kygyltasian Regional Stage (Western Verkhoyanie) in order to clarify the taxonomic composition and the age of the Upper Kygyltasian floristic association. The dominant cordaite leaves in the association were studied using the morphological and microstructural methods. This made it possible to clarify the previous paleontological definitions of the genus Noeggerathiopsis and bring them in line with modern taxonomy. The species Noeggerathiopsis heteroclitus Tolstych and N. khorokytica Tolstych were validated for type specimens. The following species were identified from the Upper Kygyltas Subformation of the Khorokyt section: Cordaites heteroclitus (Tolstych), C. cf. neuburgae Gluchova, C. cf. zalesskyi Durante, C. krychtofovichii (Radczenko), Cordaites ? khorokytica (Tolstych), Cordaites sp. sp. sp. sp. Rufloria ( Praerufloria ) Sphenophyllum cf. Sphenophyllum ? sp., Sphenopteris sp., Paracalamites sp. Based on the results of the study, the Upper Kygyltasian floristic association of the Western Verkhoyansk Region was compared with floristic associations of the Alykaeva Formation (Kuzbass) and the Upper Kata Subformation (Tunguska basin). From the above, the Late Carboniferous age of the upper part of the Kygyltasian Regional Stage follows. The results obtained are in good agreement with the correlation of the Verkhoyanian Carboniferous-Permian deposits for marine invertebrates.