Palynological zonation of the Late Devonian and Early Carboniferous of the Avon Gorge, southwest England

Well-preserved miospore assemblages are recorded from the Upper Portishead Beds, Shirehampton Beds, and the base of the Lower Limestone Shales in the classic Avon Gorge section, which displays a continuous transition from continental to marine environments. The palynofloras are assigned to the miospore zonation scheme established for the Late Devonian-Early Carboneferous of southern Ireland. The miospore assemblages from the upper part of the Portishead Beds are assigned to the Retispora lepidophyta-Knoxisporites literatus (LL) Biozone; an assemblage from the Rhacophyton Bed at the base of the Shirehampton Beds is attributed to the Retispora lepidophyta-Verrucosisporites nitidus (LN) Biozone. Both of these biozones are latest Famennian in age. Miospore assemblages from the main part of the overlying Shirehampton Beds are assigned to the Early Carboniferous Cristatisporites hibernicus-Umbonatisporites distinctus (HD) Biozone. An assemblage from the base of the overlying Lower Limestone Shales is also assigned to the HD Biozone but is distinguished from the preceding HD assemblages by the appearance of Umbonatisporites distinctus Clayton, 1971. The Devonian-Carboniferous boundary is placed within a 4 m interval above the Rhacophyton Bed in the basal part of the Shirehampton Beds.