Geologicheskii Vestnik

The fi rst description of the Frasnian deposits at the Lake Yalangaskul region is given. Their thickness is maximal for the Southern Urals (about 2500 m). The section is composed of greywackes and cherts of the upper part of the Ulutau formation, the Mukasevo formation and the lower part of the Biyagoda formation. The thickness of cherts and greywackes, and their quantitative ratio vary. This leads to the lenticular structure of the Frasnian deposits. This is most clearly seen in the lower level of the Biyagoda formation. Three lenses are distinguished in it: Yalangas, Idyash-Kuskarovo and Khudolaz. Their size and composition of clastic material diff er. The Yalangas lens is composed of an acidic volcanic clastic. Its thickness is 350 m, length is about 30 km. The 150 m-thick Idyash-Kuskarovo lens is composed of volcanic clastic material of diff erent composition. The Khudolaz lens has a thickness of 1500 m and a length of more than 30 km. Khudolaz lens greywackes are composed of quartz, plagioclase, fragments of magmatic, metamorphic and sedimentary rocks. Lenses are cross sections of deep-water fans. The fi rst two are relatively small. The Khudolaz lens is a cross section of a large fan cone consisting of several blades. The formation of a Khudolaz lentil is correlated with the global Upper Kellwasser event.

the Ulutau formation, the Mukasevo formation, Biyagoda formation, greywacke, turbidite, deep-water fan, the Upper Devonian, the Frasnian, global event, Upper Kellwasser, South Urals

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