Geological Magazine

Carbon isotope stratigraphy and the problem of a pre-Tommotian Stage in Siberia

a1 Department of Geosciences, Historical Geology and Palaeontology, Uppsala University, Norbyvägen 22, SE-752 36 Uppsala, Sweden
a2 Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden
a3 Institute of Geology, Russian Academy of Sciences, Pyzhevskij per. 7, 109017 Moscow Zh-17, Russia
a4 OBP 23, Petroleum Development Oman, PO Box 113, 113 Muscat, Sultanate of Oman
a5 Department of Geology and Geochemistry, Stockholm University, SE-106 91 Stockholm, Sweden
a6 Institute of Geological Sciences, Russian Academy of Sciences (Siberian Branch), Pr. Lenina 39, 677020 Yakutsk, Sakha, Russia


Carbon isotopic oscillations are useful to elucidate the stratigraphy and biogeochemical events around the Precambrian–Cambrian transition. New isotopic data from the Manykaj and Emyaksin formations of the eastern Anabar Uplift (Siberia) help to correlate the Lower Cambrian and Neoproterozoic–Cambrian transitional beds across the Siberian Platform. The similarity of trends and amplitudes of the carbon isotopic curves, together with biostratigraphic and sequence-stratigraphic markers from the Anabar Uplift, provide a precise correlation with the southern part of the Siberian Platform. Diagenesis of argillaceous limestones of the Emyaksin Formation has apparently not affected the primary isotopic variations. The resulting curve is nearly identical in sections about 100 km apart in the Tommotian–Atdabanian portion of the formation. Relatively frequent and pronounced isotopic oscillations in the lower beds of the Emyaksin Formation fit between features I and II of the southern Siberian isotopic reference scale but are undetected therein owing to the depositional hiatus at the base of the Tommotian Stage in its type section. This confirms the transgressive onlap from the north suggested by previous studies, and makes the appearance of the Cambrian skeletal fossils on the Siberian Platform less abrupt. The hiatus in the south appears to embrace at least two biostratigraphic zones as recognized in the north. The case is strengthened for a pre-Tommotian Cambrian Stage in Siberia, the biostratigraphic framework for which has been elaborated earlier.

(Received October 17 2000)
(Accepted May 8 2001)

c1 Author for correspondence: