Mean grain size fluctuations of the siliciclastic component in the Aizpute-41 core: implication for end-Ordovician glaciation

The article deals with grain size distribution of the insoluble residue of Upper Ordovician carbonate rocks of the Baltoscandian Basin in the West Latvian Aizpute-41 core. Great fluctuations in mean grain size in the sections of the Pirgu (uppermost Katian) and Porkuni (Hirnantian) stages are considered as indications of eustatic sea level fluctuations, pointing to the glaciation in the Hirnantian and its prelude in Pirgu time. An alternative cause of grain size fluctuations might be the up-and-down tectonic movements. Nevertheless, the synchronicity of cessation of fluctuations with the end of the Hirnantian glaciation supports the glaciation-related reason