A proposed crinoid zonation of the Devonian deposits of eastern Transbaikal

Abstract

Devonian deposits of eastern Transbaikal, Russia, are widely distributed in the Onon, Argun and Upper Amur terranes, each with a different geological development history. Two lithofacies are represented in the geological section: carbonate volcanogenic terrigenous (Onon terrane) and terrigenous carbonate (Argun and Upper Amur terranes), with strata in the latter characterized by abundant fossil remains, especially numerous crinoids and brachiopods. Brachiopod assemblages are stated for each strata of the Transbaikal Devonian. A crinoid biostratigraphic zonation is proposed within the Mongol Okhotsk fold belt as follows: Scyphocrinites mariannae, Costatocrinus bicostatus and Tastjicrinus paucicostatus (Lower Lochkovian); Amazaricrinus ildicanensis (Pragian); Paradecacrinus orientalis (Emsian); Raricrinus minimus and Vasticrinus vastus (Eifelian); Ononicrinus gracilis (Givetian); Hexacrinites? stukalinae sp. nov. (Frasnian) and Platycrinites? subtuberosus (Upper Famennian). Local and regional crinoid ages accord well with those of brachiopods. Lateral distribution of faunal assemblages allows regional correlation.