A new Late Pennsylvanian floral assemblage from the Douro Basin, Portugal

The Douro Basin (lower Gzhelian/lower Stephanian C, Upper Pennsylvanian; NW Portugal) is one of the richest continental sedimentary basins in fossil floras of late Carboniferous age in Portugal. Recent field work carried out in the Douro Basin allowed to report a new fossil site, of potential Lagerstatte quality, found in the Montes da Costa (Ermesinde) region. This new fossil locality preserves exceptional palaeontological, stratigraphic, lithological, and tectonic structural features of great scientific interest. An exceptional record of sudden catastrophic flooding events represents one of the most remarkable geological records documented in this new locality. In the palaeontological context, the plant assemblage described comprises a well-preserved and very diversified macroflora of early Gzhelian age, consisting of several fossil taxa belonging mainly to genera and species of Pteridopsida, Pteridospermopsida, and Sphenopsida. Its fossil records are essentially parautochthonous deposits, but several Calamites trunks preserved in autochthonous position were documented. Within the studied plant assemblage, a new species of arborescent marattialean fern, Acitheca murphyi sp. nov., is described, and several new floral occurrences are first reported in the Portuguese Carboniferous. Here, we analyse the palaeoecological, palaeoenvironmental, and palaeoclimatic conditions of the new palaeobotanical data. Additionally, there was undertaken an extensive comparative study of Gzhelian (Stephanian C-early Autunian) age macrofloras from different localities of Europe and North America. Together with these results, a significant macrofloral biostratigraphic gap for the Kasimovian stage in the Appalachian region (West Virginia, USA) is demonstrated to be correlated to the Late Pennsylvanian of Portugal, and its palaeogeographic significance is assessed.