Biostratigraphy and geochemistry of Upper Silurian brachiopods from the Timan-Pechora region (Russia)

Abstract

This paper presents biostratigraphical and geochemical (trace element, stable isotopes) data relating to the Upper Silurian brachiopods from Bol'shezemel'skaya Tundra, Timan-Pechora region. The Upper Silurian sections exposed in this region are characterized by monotonous carbonate-deminated deposits. The brachiopod biostratigraphy is based on the evolution of athyrids. Trace element contents (Sr, Mn, Na, Fe) and shell microstructures of nonluminescent (NL) brachiopods compare well with those of modern brachiopods. Isotopic data derived from Upper Silurian NL brachiopod samples show a significant negative delta13C excursion during the Early Ludfordian (Didymothyris didyma Zone). Above this horizon, increasing delta 13C values can be observed both for brachiopods from the northeastern edge of the East European Platform (samples from the Baltic area) and carbonate whole rock samples from Austria and Australia. The Middle Ludfordian isotope variations is probably a worldwide chemostratigraphical marker level, although the magnitudes of positive isotope excursions show large interregional differences, which may be related to regional oceanographical differences.