The Mid-Carboniferous boundary in the eastern slope of the Southern and Middle Urals: carbon and oxygen isotopic composition in limestones

Abstract

Research subject. Limestones of the Mid-Carboniferous boundary interval of the Urals eastern slope (“Khudo-laz”, “Khudolaz-gully” and “Bolshoy Kizil” sections at the Southern Urals, as well as “Iset quarry” and “Lugovaya” sections in the Middle Urals) are considered. Methods. Carbon and oxygen isotopic composition in bulk samples was analyzed.Results. The carbon and oxygen isotopic composition in carbonate deposits of the Serpukhovian-Bashkirian boundary interval in the sections of the Southern and Middle Urals eastern slope was studied. It is shown that the value of δ13C in the most complete sections varies from 1.5 to 3.8‰, while δ18O – from 23.1 to 30.7‰. Conclusions. Variations in the carbon and oxygen isotopic composition are associated with both global and local events. In the East Uralian basins (northern periphery of Paleotethys), the shift in carbon isotopic composition of carbonate sediments appeared in the Late Serpukhovian. In some cases, this trend correlates with the positive excursion of δ18O, which is most likely associated with the global short-term cooling (glaciation).

Keywords

• eastern slope of the urals
• the lower and middle carboniferous sub-systems
• the mid-carboniferous boundary
• biostratigraphy
• carbon and oxygen isotopes
• unconformity (hiatus)