Age of the upper part of the Devonian tuffogeneous unit from the Middle Timan (the Pizhma river) according to the results of U-Pb (SIMS)-zircon dating

An important feature of the Devonian sediments in the Timan Ridge is that they contain basaltic volcanic rocks. The paper provides results of study of tuff-rich interlayers in the Valsovskaya and Ust’chirkinskaya Formations located in the Pizhma River (Middle Timan) from which zircons were extracted. U-Pb dating of zircons yielded the ages of 376.8 ± 6.7 Ma and 372.4 ± 8.3 Ma respectively. These ages correspond to Late Frasnian and Early Famennian and contradict the biostratigraphic data according to which the age of the rocks is Late Givetian and Early Frasnian. Rejuvenation of the zircon ages is supposed to be related to the time-extended crystallization of zircon crystals.