Reference section of the Uk Formation of the Upper Riphean (Karatavian) in the Alatau anticlinorium (Southern Urals)

Abstract

Research subject. The deposits of the Uk Formation of the Upper Riphean (Karatavian) in the Alatau anticlinorium (Southern Urals) were studied in the section of the right bank of Basu river and its tribute Manaysu located to the east of the Kulmas settlement.Results. The structure of the sections of Uk Formation along Basu River (Kulmas) in the Alatau anticlinorium and its stratotype at the Yuryzan river near town of Ust-Katav in the Suleimanovo anticline is identical: the Lower Uk Subformation is represented by irregular alternation of sandstones, siltstones and shales with rare layers of limestones and dolomites with Patomella kelleri Raaben and Tungussia bassa Kryl. stromatolites and microphytolites of the IV complex, while the Upper Uk – by limestones with Linella ukka Kryl. and Linella simica Kryl. stromatolites and microphytolites of the IV complex. However, the sandstones and siltstones of the Lower Uk Subformation in the stratotype at the Yuryuzan river (Ust-Katav) are polymictic, while in the reference section along Basu river (Kulmas) they have mostly quartz composition. These petrographic features may be a result of different provenance. In the rocks of Uk Formation in the Basu section (Kulmas), the epigenetic processes (dolomitization and silicification) are strongly manifested. In the limestones of the Upper Uk Formation the caverns and fractures along with layers enriched by a bitumen (?) are observed.Conclusions. The reference section of the Uk Formation along the river Basu (Kulmas) is proposed as a hypostratotype, in which the deposits of the lower subformation of the Uk suite are most fully represented in comparison with the stratotype along the river Yuryuzan (Ust-Katav). Cavernous-fractured limestones of the Uk Formation with layers enriched by a bitumen (?), may be regarded as an interesting search object for hydrocarbons, taking into account that a large hydrocarbon deposit has been discovered in the silicified cavernous-fractured dolomites of Kamovskaya Formation of the Upper Riphean of the Siberian platform.