Knoll, AndrewKaufman, Alan J.Semikhatov, Mikhail A.Grotzinger, John P.Adams, William2009-06-231995Knoll, Andrew H., Alan J. Kaufman, Mikhail A. Semikhatov, John P. Grotzinger, and William Adams. 1995. Sizing up the sub-Tommotian unconformity in Siberia. Geology 23, no. 12: 1139-1143.0091-7613http://nrs.harvard.edu/urn-3:HUL.InstRepos:3119537Sedimentary rocks in the western Anabar region, northwestern Siberia, preserve an exceptional record of evolution and biogeochemical events near the Proterozoic-Cambrian boundary. Carbon isotopic data on petrographically and geochemically screened samples collected at 1 to 2 m intervals support correlation of the lower Anabar succession (Staraya Reckha and lower Manykai Formations) with sub-Tommotian carbonates of the Ust'-Yu-doma Formation in southeastern Siberia, In contrast, the upper Manykai and most of the overlying Medvezhya Formation appear to preserve a sedimentary and paleontological record of an evolutionarily important time interval represented in southeastern Siberia only by the sub-Tommotian unconformity. Correlation of the Anabar section with other northern Siberian successions that contain well-dated volcanic rocks permits the estimate that the sub-Tommotian unconformity in southeastern Siberia spans approximately 3 to 6 m.y. Diverse small shelly fossils (but not archaeocyathans) previously thought to mark the base of the Tommotian Stage evolved sequentially throughout this earlier interval.en-US10.1130/0091-7613(1995)023<1139:SUTSTU>2.3.CO;2