New Carbon-Isotope, Conodont, and Magnetostratigraphic Data from the Key Kulyumbe River Section (NW Siberia) and the Problem of Location of the Cambrian-Ordovician Boundary on the Siberian Platform

The Kulyumbe River section (NW of the Siberian Platform) is one of the most complete, best exposed, well-studied, and relatively easily accessible Cambrian-Ordovician (Cm-O) successions on the entire Siberian Platform. It is a key section for regional correlation of the Furongian-lower Ordovician interval in Siberia. However, the exact position of the Cm-O boundary as well as the boundaries of the global Ordovician stages in the section is still a matter of debate. We present new magneto-, chemo-, and biostratigraphic data, which allow us to discuss the position of the Cm-O and Tremadocian-Floian boundaries in the Kulyumbe River section. These data determine a new confident levels for correlation of transitional Siberian Cm-O layers with the International Stratigraphic Scale.