Plant Taphonomy and Paleoecology of Late Pennsylvanian Intramontane Wetlands in the Graissessac-Lodève Basin (Languedoc, France)

The Late Pennsylvanian Graissessac-Lodève basin is a small, fluvio-palustrine depocenter located in the southern part of the Massif Central (France). A taphonomic and sedimentologic study carried out in this area allows a reconstruction of Late Carboniferous vegetation in an intramontane context. The paleoecology of such limnic settings is poorly known, and this study permits detailed comparison with paralic basins for the first time. The Graissessac peat mires developed in abandoned fluvial channels, in floodplains, and above distal alluvial fans. The vegetation was dominated by monospecific stands of the arborescent lycopsid Sigillaria brardii, whereas the tree fern Psaronius occurred during the later stages of mire accretion. This is in contrast to coeval North American peat mires, which generally were dominated by tree ferns and pteridosperms throughout the mire profile. Stephanian floodplains and distal alluvial fans of the Graissessac-Lodève Basin were devoid of vegetation, with the exception of isolated thickets of sphenopsids that were composed of Calamites and Sphenophyllum. These plants were found growing in situ in the floodplain mudstones as well as in fine-grained sands of secondary channels. Parautochthonous foliage assemblages of ferns and pteridosperms found in floodplain mudstones represent the most diverse plant community. The plants supplying these remains were growing in exposed areas close to floodplains. Large logs attributed to cordaitaleans and monotypic assemblages of large Cordaites leaves were found in fluvial sediments, and suggest that the plants were riparian elements in the basin.