AbstractA brief description of the carboniferous succession on Halkyn Mountain, North Wales, together with a map illustrating the areal distribution of upper Viséan carbonate and Namurian non‐carbonate lithologies, is presented. The upper Vistan carbonates have been divided into four major units termed in ascending order: A1 (pelsparites and biopelsparites); A2 (alternating biopelmicsparites, non‐argillaceous biomicrites and micrites); B1 (argillaceous calcite siltstones); B2 (alternating non‐argillaceous and argillaceous biomicrites and micrites). Analysis of the distribution of microfacies within each unit indicates that during upper V i s h times, deposition of shallow water, off‐shore, carbonate sand banks alternated with, and finally gave way to, the deposition of in‐shore, lagoonal carbonate muds. The presence of an erosional surface at the top of Unit B2 suggests that a period of emergence took place prior to the deposition of the succeeding Namurian bedded cherts. The cherts can be differentiated into three major lithologies which exhibit characteristics that are consistent with cyclic deposition in a marginal, restri