About the Lower Boundary of Artinskian in Permian of the Verkhoyansk Region
Artinskian-Sakmarian boundary in the Verkhoyansk region is located within the lithological monotonous and paleontological poor lower part of the Echian horizon. To replace of extensive Arkachanian ammonoid association in the base of Artinskian Endybalian association appeared which was taxonomic depleted and locally distributed. It is proposed to consider as the main indicator of Artinskian lower boundary the appearance of subspecies Neoshumardites triceps hyperboreus, which morphologically and genetically is very similar to the Early Artinskian Neoshumardites of South Urals. The spread of the South Urals Neoshumardites in the Verkhoyansk region was probably due to the period of maximum warming of seawater, which occurred at the Sakmarian-Artinskian transition. As a result of this warming, the brief invasion of the biota of the Urals occurred, which was later superseded by Siberian invertebrate taxa. In the absence of the ammonoids findings to determine of Artinskian lower boundary it is possible to use a change in section of brachiopods genus Jakutoproductus by Inoceramus-like bivalves. Paleontological characteristics of the main sections, located in the mouth of the Dielendzha river (the Tumara river basin) and the Arkachan-Echij interfluves are briefly considered.