INTERREGIONAL CORRELATION OF THE MIDDLE FRASNIAN (UPPER DEVONOIAN) OF THE NORTH-WEST OF THE RUSSIAN PLATE AND THE EAST OF THE PECHORA PLATE: AN ECOGEOCHEMICAL ASPECT

Abstract

The paper provides an example of the first stratigraphic application of ecogeochemical method based on the analysis of the carbon isotope values in conodont elements. The method is based on hypothesis of almost isochronic regime change (at least within the basin) in isotope fractionation of carbon in pelagic ecosystems which is reflected and kept in carbon isotope composition of conodont elements. This method has been used to compare between different facial Frasnian sequences of the northwestern Russian Plate (coastal marine facies) and eastern Pechora Plate (depression facies). There were traces of three isotope excursions: negative in the vicinity of the MN5 zone basement (domanic horizon basement), negative at the boundary between the MN5 and MN6 zones, and double positive excursion in the upper MN6 zone. The amplitude of excursions is usually much less in the deep-water facies. The similarity of variations in carbon isotope composition of conodont elements in geographically remote and facially different Fransnian sedimentary sequences of the northwestern Russian Plate and eastern Pechora Plate confirms the possibility of using this parameter for stratigraphic correlation.