We have revisited the stratotype area of the Lower Formation of the Second Bani Group, west of Tagounite in the Moroccan Anti-Atlas, and sampled brachiopods and trilobites from its uppermost quartzitic horizons. In addition to those brachiopods listed in previous papers on the region, we have found Plectothyrella sp. and Kinnella sp. Both genera are exclusive of the pandemic Hirnantia fauna, which allows confirmation of a Hirnantian age for the upper member of the Lower Second Bani Formation. By contrast, the lower member of the same unit has yielded Katian brachiopods and trilobites, such as Eostropheodonta intermedia, Destombesium sp., Hirnantia sp. (species other than H. sagittifera), Actinopeltis aff. insocialis, Mucronaspis termieri and Cekovia aff. perplexa. According to the lithostratigraphic framework, the Katian/Hirnantian boundary lies within the Lower Formation of the Second Bani Group and lithostratigraphically correlative horizons, such as those reported in Bou Ingarf. The latter were mainly dated as a result of lithostratigraphic and sequential correlations and, based on correlation with the Tagounite area, are in need of revision. The age of the lower part of the chitinozoan Tanuchinita elongata Biozone should be re-evaluated, and the suggested delayed onset of the Hirnantian glaciation reconsidered.

Trabajo presentado en el 60th Annual Meeting of the Palaeontological Association, celebrado en Lyon (Francia), del 14 al 17 de diciembre de 2016

Peer reviewed