A thick series of carbonates, widespread on the eastem slope of the South Urals in the center of the
Magnitogorsk Megasynclinorium constitute the Kizil Formation established by L.S. Librovitch [1936).
Sedimentation of the Kizil Formation occurred in a shallow-water shelfbasin from the Late Viséan, through-
out the Serpukhovian and most of the Bashkirian, and was terminated in the Askynbashian by the raising of
a carbonate platform.  The Kizil Formation extends along the Ural, Bolshoi Kizil and Khudolaz rivers. lt
overlies the volcanic rocks of the Berezovskaya Formation and is overlain with an unconformity by conglom-
erates of the Urtazym Formation of Moscovian age.  Due to the considerable thickness of the formation and
the abundance of small algal bioherms and biostromes, this sequence of rocks was described as a reefoid
formation [Korolyuk et al., 1983].  The largest bioherms are found in the Bashkirian portion of the section
[Shchekotova, 1978].
      Much research has been done on the biostratigraphy and fossils of the Kizil Formation [lvanova et
al., 1972; Ivanova, 1975; Kochetkova et al., 1977; Kochetkova, 1983; Simonova, 1990; Stepanova, 1997;
Stepanova, Kucheva, 2006; Zainakaeva, 2004; Kulagina et al., 2001, 2002; Kulagina, 2007].
      The outcrops of the Kizil Formation along the Khudolaz River constitute the stratotype section of the
regional stratigraphic subdivisions of the eastern subregion of the Urals, and the hypostratotype of the
Averinian (Upper Viséan) [Stepanova, Kucheva, 2006, whereas the outcrops of carbonates along the Bolshoi
Kizil River constitute the stratotype of the Kizil Formation.  The stratotype section along the Bolshoi Kizil
River shows a faunal assemblage of the bioherm facies accumulated in an open shallow marine basin with
many brachiopod shoals and banks, and with algal and coral bioherms.