Home – Home – Jornals – Russian Geology and Geophysics 2002 number 3

The Riphean (1500-1450 to 1000-950 Ma, from ⁴⁰Ar/³⁹Ar and K/Ar age methods) section of petroliferous peritidal carbonates in the Baikit uplift in the western Siberian Platform contains five sequences, each divided into three to five subsequences, distinguished on the basis of sediment logy and isotope geochemistry. The five sequences deposited in the period from 80 to 100 Ma and reflect major fluctuations of the sea level. The stability of 13C estimates is confirmed by petro-graphical, geochemical, and isotope data (over 350 analyses), which show that early diagenic dolomites may retain primary ¹³C signal subject to only slight changes. The ¹³C values in the lowermost carbonates (1450-1350 Ma, from isotope data) are about zero (-0.2 to 0.5). The overlying section contains long intervals with low positive d¹³C values of 0.5 to 2.0, occasionally up to 3.0, alternating with shorter intervals dominated by negative ¹³C values (to 2.2). The negative shifts correspond to the deposition of lower Yurubchen (~1350 Ma), upper Yurubchen-Dolgokta (1270-250 Ma), Kopcher (1100-1080 Ma), and upper Yukta-lower Tokur (about 1000 Ma) subsequences. The main trends in the sea level fluctuations correlate well with ¹³C variations: The negative isotopic shifts coincide with the boundaries of the five major sequences; the intervals with medium positive ¹³C record high sea stand and correspond to the periods of carbonate shelf aggradation; low ¹³C values often correlate with the boundaries and the lower segments of the subsequences. Isotope and geological data from other regions indicate that the low sea stand periods correlated with the boundaries of the sedimentary subsequences in the Baikit uplift are most likely associated with global geological events and reflect eustatic fluctuations.