In Western Siberia, exploration for petroleum in Mesozoic sediments has uncovered carbonate rocks in deep drill holes (1-3). Lithological-paleogeographical maps of Upper Silurian, Devonian, and Lower Carboniferous formations (1) show Western Siberia to be a region of vast deposition of carbonate sediments. The sea, which transgressed from the northwest, covered much of the West Siberian Plain and moved far southward into Central Asia and the Altay-Sayan region
