Home – Home – Jornals – Russian Geology and Geophysics 2016 number 2

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 a carbonate-terrigenous section near Nabiullino Village. They belong to important cosmopolitan taxa which permit distinguishing biostratigraphic units corresponding to the North Atlantic standard conodont scale. Successions of Middle and Upper Ordovician conodont and chitinozoan assemblages are detected 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 owing to their wide geographic range. A positive δ¹³C excursion of 3.3 ‰ has been first recorded in the Nabiullino section (West Zilair zone), suggesting the initial stage of the HICE isotopic event 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.