Carbonate successions of the early Lower Devonian (Lochkovian-early Pragian) from the Mindigulovo section (West Zilair Zone, western slope of the South Urals) can be globally correlated using diverse conodont faunas. The number of the documented widespread or cosmopolitan taxa of the Lochkovian and early Pragian age enables the definition of globally recognized conodont successions and the establishment of a refined regional conodont biozonal scale. The present three-fold global subdivision of the Lochkovian Stage can be applied as well to the studied area. The Lochkovian in the South Urals is represented by two Horizons (regional terminology) with different facies development: 1. The Siyak Horizon of the lower Lochkovian characterized by the dominance of shallow-water organogenic limestones of the hesperius-optima and optima-omoalpha Zones, and 2. The Sherlubai Horizon of the middle and upper Lochkovian age characterized by the dominance of carbonate-terrigenous successions. The middle and upper Lochkovian is subdivided into five biozones (using a binominal system): omoalpha-eoeleanorae, eoeleanorae-eleanorae, eleanorae-trigonicus, trigonicus-pandora beta and pandora beta-sulcatus eta/steinachensis. The Lochkovian-Pragian boundary and the early Pragian time are determined by the presence of eognathodontid and icriodontid stocks. The established regional conodont zonal scale in the South Urals provides a solid basis for refined correlation with the Lochkovian-early Pragian carbonate rocks of peri-Gondwana and Euramerica. •

Biostratigraphic subdivision and correlation of Ordovician different-facies sections on the western slope of the Southern Urals are carried out based on conodonts and chitinozoans. Upper Ordovician conodonts are defined in the West Zilair zone, in the carbonate-terrigenous section near Nabiullino Village. They belong to important cosmopolitan taxa which allow distinguishing biostratigraphic units corresponding to the North Atlantic standard conodont scale. Successions of Middle and Upper Ordovician conodont and chitinozoan assemblages are identified in the terrigenous-siliceous sections of the East Zilair zone. Middle Ordovician chitinozoans are found in the Uraltau zone, in the metamorphic rocks of the Belekei Formation of the Suvanyak complex, previously assigned to the Precambrian. Most of the taxa in the conodont and chitinozoan assemblages have a good correlation potential due to their wide geographic range. A positive δ13C excursion of 3.3‰ was first recorded in the Nabiullino section (West Zilair zone), suggesting the initial phase of the HICE isotopic events in the Southern Urals. The development of shallow-water conodont biofacies at the top of the section suggests a sea level fall in the Late Ordovician.

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