CARBON, OXYGEN, STRONTIUM, AND SULFUR ISOTOPIC COMPOSITIONS IN LATE PRECAMBRIAN ROCKS OF THE PATOM COMPLEX, CENTRAL SIBERIA: COMMUNICATION 2. NATURE OF CARBONATES WITH ULTRALOW AND ULTRAHIGH δ13C VALUES

Abstract

The Patom Complex is characterized by a unique association of carbonate rocks with ultralow (≤8‰) and ultrahigh (>6‰) δ13C values. The thickness, stable isotopic composition along the strike, and lithological and geochemical parameters suggest that these rocks could not form as a result of short-term local events or epigenetic processes. Ultralow δ13C values (less than -8‰) in carbonate rocks of the Zhuya Group, which substantially exceed all the known negative C isotope anomalies in thickness (up to 1000 m) and amplitude (δ13C = -10 ± 2‰), point to sedimentation under conditions of extreme "contamination" of water column by oxidized isotopically light organic (hereafter, light) carbon. The decisive role in this contamination belonged to melting and oxidation of huge volumes of methane hydrates accumulated in sediments during the powerful and prolonged Early Vendian glacial epoch. The accumulation of δ13C-depleted carbonates was preceded by the deposition of carbonates with anomalously high δ13C values. These carbonates formed at high rates of the burial of organic matter and methane in sediments during periods when the sedimentation basin consumed carbon dioxide from the atmosphere and organic carbon was conserved in sediments. © Pleiades Publishing, Inc. 2006.