New data on age of Lower Devonian deposits of the West-Magnitogorsk zone of the Southern Urals

Lower Devonian deposits of the West-Magnitogorsk zone of the Southern Urals in some regions are represented by Mansurovo, Iltibanovo, Uskul’ and Ryskuzhino strata. For a long time these strata were considered as a part of the Irendyk suite due to the macroscopic similarity, insufficiency of biostratigraphic data and complicated tectonic structure of the territory. After the adoption a new Stratigraphic scheme of the Urals in 1993 and the geological survey, carried out in the study area, the age identity with the Lower Devonian Mazovo suite was established. Based on the results of detailed stratigraphic and geological studies of the Devonian sections, V. A. Maslov and O. V. Artyushkova decided to consider the Lower Devonian strata as independent units. The Uskul’ strata are located in the Uzynkyr subzone of the West-Magnitogorsk zone (Republic of Bashkortostan, the southwestern shore of the Uscul’ Lake and the northwestern slope of the mountain of the same name). They are composed of volcaniclastic, carbonaceous and siliceous rocks, rarely volcanic rocks. The apparent thickness of the section is approximately 700 m. For a long time, the age of the Uskul’ strata was determined by the fauna from the lentiform limestones located in the upper part of the section. The article presents the first finds of macrofauna from a rhythmic packet of tephroturbidites lying in the lower part of the section. The fauna is represented by fossils of brachiopods and crinoids. Brachiopods correspond to the Early Devonian Pragian-Emsian age. The new data allow to speak about close time of sedimentation tephroturbidites and overlying limestones, and in general to determine the age of the Uscul’ strata as Pragian-Early Emsian based on conodonts.