The Riphean (1500–1450 to 1000–950 Ma, 40Ar/39Ar, K/Ar) section of petroliferous peritidal carbonates in the Baikit uplift (western Siberian Platform) contains five sequences, each divided into three to five subsequences, distinguished on the basis of sedimentology and isotope geochemistry. The five sequences deposited in the period from 80 to 100 Ma and reflect major sea-level changes. The stability of δ13C estimates is confirmed by petrographical, geochemical, and isotopic data (over 350 analyses) showing that early diagenetic dolomites may retain almost invariable primary δ13C signal. The δ13C values in the lowermost carbonates (1450–1350 Ma) are about zero (–0.2 to 0.5 ‰). The overlying section contains long intervals with low positive δ13C of 0.5 to 2.0, occasionally to 3.0 ‰, alternating with shorter intervals of mostly negative δ13C (to –2.2 ‰). The negative shifts correspond to the deposition of the lower Yurubchen (∼1350 Ma), upper Yurubchen-Dolgokta (1270–1250 Ma), Kopchera (1100–1080 Ma), and upper Yukta-lower Tokur (about 1000 Ma) sections. The main trends in the sea-level fluctuations correlate well with the δ13C record: The negative excursions coincide with the boundaries of the five major sequences; the intervals with medium positive δ13C record high sea stand and correspond to the periods of carbonate shelf aggradation; most of low δ13C values correlate with the boundaries and lower parts of the subsequences. Isotopic and geological data from other regions indicate that the lowstand periods marked by the subsequence boundaries in the Baikit uplift are most likely associated with global geological events and reflect eustatic changes.

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