Palaeobotany of the Pennsylvanian (mid-Bolsovian–Cantabrian; Moscovian) Warwickshire Group of the Bristol Coalfield, U.K.: Biostratigraphy and palaeoecology

The Bristol Coalfield of southwest Britain, although intensively studied in the early history of palaeobotany, has received little attention for 75 years. Here we review the palaeobotany of the mid-Bolsovian to Cantabrian (Moscovian) Warwickshire Group of the Bristol Coalfield, which comprises, from base to top, the Winterbourne, Pennant Sandstone and Grovesend formations. Based on an investigation of all available adpression and sandstone-cast plant assemblages in a facies context, we develop a new system of biostratigraphical zonation and elucidate palaeoecology. Our key findings are: (1) Using the new biozonation we identify a stratigraphical gap encompassing the early to mid-Asturian, occurring between the mid- and late Bolsovian Pennant Sandstone and the late Asturian Grovesend formations. This tectonic-induced stratigraphical gap most likely relates to the Leonian Phase of the Variscan uplift and can be correlated with contemporaneous hiatuses in the South Wales and other European coalfields. (2) We recognise a diverse patchwork of plant communities as follows: Peat mires of the Bolsovian Winterbourne and Pennant Sandstone formations were dominated by lepidodendrids and ferns, but were replaced by tree-fern and fern-dominated mires in the late Asturian Grovesend Formation. Clastic swamps fringed these mires and were characterised by a diversity of pteridosperm, calamitaleans and ferns. Riparian communities associated with the coarse-grained deposits of large-scale braided fluvial systems that vertically alternate with the coals/shales, variously comprised Sigillaria, calamitaleans and cordaitaleans, with pockets of pteridosperms and calamitaleans surrounding channel abandonments. In addition, large cordaitaleans were common in drier interfluve and/or hinterland areas. Switching between stable mire communities and disturbed fluvial communities either reflects autocyclic channel switching or allocyclic alternations driven by climate change.

► A full review of the Pennsylvanian palaeobotany of the Bristol Coalfield.
► We have produced the first megafloral biozonation scheme for the coalfield.
► Sequence dated as mid-Bolsovian to Cantabrian.
► A tectonic-induced hiatus is identified; correlating with other coalfields.
► We also discuss palaeoecological interpretations.