Carbon-isotope events across the Precambrian/Cambrian boundary on the Siberian Platform

• Published in: Nature (London) 1986-03, Vol.320 (6059), p.258-259
• Main Authors: Magaritz, Mordeckai, Holser, William T, Kirschvink, Joseph L
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Humanities and Social Sciences; Isotope geochemistry; Isotope geochemistry. Geochronology; letter; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/320258a0

Variations of marine isotopes with time have been observed through the Phanerozoic 1,2 , in association with some period boundaries: Pleistocene/Holocene 3 , Cretaceous/Tertiary 4 , Permo-Triassic 5,6 and Frasnian/Fammenian 7 . Most of these changes are associated with extinction events, reflecting changes in life on Earth. One of the major biological changes in Earth's history occurred near the end of Proterozoic time, with widespread increase of bio-mineralization and the appearance of shelly fauna 8–10 . We present here an initial survey of carbon isotope ratios in a section on the Siberian Platform that spans the Proterozoic/Palaeozoic boundary. After a high of δ 13 C = + 3.4‰, 15 m below the boundary, δ 13 C drops sharply in two cycles across the boundary, to δ 13 C = −2‰, near the end of the Tommotian Stage. These variations suggest an initial bloom of biomass in late Vendian time corresponding to the dramatic diversification that must have preceeded the widespread appearance of new taxa in the Cambrian fossil record.