New insights into Cadomian basin evolution and stratigraphic affiliation of sedimentary units of Saxo-Thuringia, Germany: Part 2—detrital zircon U–Pb ages

Abstract

New LA-ICP-MS detrital zircon U–Pb age data from Saxo-Thuringia provide improved constraints on the evolution of Neoproterozoic to Early Ordovician sedimentary basins along the northern margin of Gondwana . Several investigated quartzitic successions previously assigned to the Neoproterozoic have robust maximum depositional ages (RMDA) of 499 ± 5 Ma (member 2 of the Clanzschwitz Group) and 485 ± 5 Ma (Seidewitz Formation), requiring their reassignment to the upper Cambrian–Lower Ordovician. The immature greywacke units of the Cadomian basement yield robust maximum depositional ages between 551 and 546 Ma, consistent with uniform deposition during the Late Neoproterozoic in a broad active continental margin setting. In contrast, Ordovician quartzites reveal variable source signatures. Some reflect exclusively recycling of Neoproterozoic (Avalonian–Cadomian orogenic belt) and older crustal material (West African Craton), while others show additionally significant input from younger Cambro–Ordovician magmatic rocks in the Saxo-Thuringian hinterland, highlighting diverse sediment sources along the Ordovician shelf margin. The detrital zircon U–Pb data confirm a West African provenance for all analysed units. Despite its younger age, a Carboniferous greywacke from the Görlitzer Schiefergebirge was also studied here due to its close lithological resemblance to Neoproterozoic greywackes and the absence of established differentiation criteria. Its detrital zircon assemblage reflects a recycled Cadomian basement signature, along with admixtures of Cambro–Ordovician zircons and juvenile grains (~ 375–370 Ma) derived from Upper Devonian magmatic rocks. In the absence of fossil evidence, this provides clear criteria to distinguish Neoproterozoic from Carboniferous greywackes in this part of Saxo-Thuringia. Graphic abstract

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