Saxo-Thuringia meets Bavaria: Paleozoic facies types in the light of current knowledge

In the Saxo-Thuringian Zone (SXZ) of the Variscides, the strict bipartite subdivision of Paleozoic marine sediments date to the beginning of the last Century. This proposition based on the observation that early Paleozoic lithologies (Bavarian facies; ba) associated with the Münchberg Gneiss Complex in the hanging wall differ significantly from underlying lithologies of the same age. Sediments of the foot wall were ascribed as the (par-)autochthonous Thuringian facies (th) of the former Saxo-Thuringian basin. In such a view, continuous sedimentation of both facies types prevailed until the early Carboniferous (Visean, ~330 Ma). Only the crystalline pile of Münchberg and associated nappes (ba) of the former distal part of the Saxo-Thuringian basin are regarded as northwestward overthrusted allochthonous units. However, such a bipartite model is not able to explain the complex architecture of the SXZ. For example, Early Carboniferous (>340 Ma) Paleozoic nappes in the Vogtland (th), the Nossen-Willsdruff- and the Elbtalschiefergebirge (th+ba) are discordantly overlain by Visean synorogenic sediments (ba+th). The long-lasting (Early Devonian-Carboniferous) accretionary tectonics in the Erzgebirge-Fichtelgebirge Complex (EFC) also precedes the proposed end of continuous sedimentation in the SXZ. Medium- to high-pressure metasedimentary nappes of the EFC exhibit the distinctive geochemical signature of early Ordovician siliciclastic rocks (th). After a concise review of the sedimentary record of the Saxo-Thuringian Zone, we present a tectono-sedimentary model explaining the spatial distribution of the sediments with the formation of the vast Peri-Gondwana shelf eventually followed by prolonged continental accretionary tectonics during the collision of Gondwana with Laurussia.