MAJOR CAMBRIAN BIOTIC BOUNDARIES IN THE NORTHERN SIBERIAN PLATFORM

Abstract

We have characterized complexes of the guide faunal groups (small-shelled fauna, archaeocyathids, trilobites, and brachiopods) and followed their stratigraphic and lateral distribution in the Cambrian deposits of the northern Siberian Platform. Eleven boundaries, where these complexes undergo major biotic transformations, have been established. The boundaries are compared with those characterized in other studies, as well as with the carbon isotope datings from different sections of the Siberian Platform. Some of the boundaries established in this study correlate well with global biotic events and with the extrema of carbon isotope ratio curves. The examples include Boundary 1, the lower boundary of the Tommotian stage; Boundary 3, the lower boundary of the Atdabanian stage; Boundary 5, the lower boundary of the Botomian stage; and Boundaries 7 and 8 marking the transition from the Lower to Middle Cambrian in the Siberian Platform. Additionally, Boundary 9 is an almost universally present lower boundary of the Triplagnostus gibbus Zone of the Amgan stage.