On a coal specimen possibly associated with the classical Mio-Pleistocene São Jorge leaf bed site, Madeira Island, Portugal

Abstract

Due to the unusual presence of coal seams within a volcanic island, the São Jorge lignite, located in the north side of Madeira Island, was since the early 19th century a magnet for naturalists. In 1854 the site was visited by Sir Charles Lyell and Georg Hartung, where both discovered a leaf-bed associated with the lignite. This finding provided key proofs to Lyell's uniformitarian theory of the formation of volcanic islands and the long-term existence of laurel forests in Macaronesia. Despite its historical importance, lignite specimens from São Jorge remain unknown to date. Recently, the study of Funchal Natural History Museum (MMF, Madeira Island, Portugal) collections revealed a coal specimen associated with the classical site of São Jorge. Here we provide a critical analysis of this specimen using historical and palaeobotanical approaches. We show that this coal is not a lignite from São Jorge and that it was not collected in ca. 1905. Historically, the São Jorge site was covered by a landslide until 1917, making it inaccessible. Furthermore, the coal is either a bituminous coal or anthracite and contains typical rhizomorph fossils of extinct Lycophytes known as Stigmaria ficoides (Sternb.) Brongn., as already indicated in the old MMF record books. The coal is most likely a late Carboniferous (Pennsylvanian, 323.4–298.9 Ma) specimen from the early 20th century British coaling industry on Madeira Island, imported from the UK, which, at some point, was erroneously labelled as originating from the 7–1.8 Ma São Jorge outcrop in Madeira.