Discovery of unknown habitats in coal-bearing flora in the Pyrenees

A new study shows how the species Sigillaria brardii – a fossil plant typical of peatlands and abundant in the flora of Europe and North America in the Upper Carboniferous – colonized new areas in the riverbeds of a large European mountain range known as the Variscan Mountains, far from their natural habitat.

This process of ecological dispersal of species has only been documented in coastal sedimentary basins known as paralyzes in the United States and northern Europe. Now a study published in the journal Paleogeography, paleoclimatology, paleoecologydescribes for the first time the colonization phenomenon of S. brardii in Variscan freshwater marshes mountain ridge, an ancient geological structure in Europe, now eroded, which still represents geological outcrops in the Pyrenees and the Catalan coastal mountain ranges.

The paper, which advances knowledge about the characteristics of forest ecosystems in the Late Carboniferous, was contributed by Aisha Tosal, Joaquim Pamies and Carles Martin-Closas from the Department of Earth and Ocean Dynamics, Faculty of Earth Sciences and Biodiversity Research Institute (IRBio) of the University of Barcelona.

Carboniferous flora of the Catalan Pyrenees

The team carried out a sedimentological, taphonomic and palaeoecological analysis in the Erilcastella basin, in the south of the Catalan Pyrenees, a geological area of ​​great scientific interest for the study of the process of creation of the Pyrenean coal basins.

Many coal mines which were exploited, correspond to old forests that turned out to be petrified. In particular, the formation of bog deposits in the Late Carboniferous (Pennsylvanian) in the Pyrenees is associated with the accumulation of peat from plants evolutionarily related to the modern Isaete (pteridophyte) lineage. These tree-like isettes of the genus Sigillaria were formerly found in swamps and marshes in the valleys of the great Varisca mountain range.

The trunks of this plant, mostly built of rather weak tissue or periderm, accumulated at the bottom of anoxic bogs and easily turned into peat. After a long geochemical ripening—sub high pressure and temperature—the accumulated peat turned into coal (of the bituminous type), which was mined in the Pyrenees in the late 19th and early 20th centuries to power steam plants in Barcelona. Later (from 1950 to 1970) the coal mines were reopened to feed small local cement plants in Barcelona.

Sigillaria brardii: When peatlands disappear

According to experts, the increase in ecological plasticity of this species is related to the time of global climate change, increasing temperature and aridity. These environmental conditions caused a reduction in the area of ​​peatlands and an increase in erosion and drainage in mountainous areas, and this could explain the new ecological distribution of the species.

“These changes reached their peak in the Lower Permian, between 300 and 273 million years ago, when finally all woody members of this pteridophyte group became extinct,” the research team concludes.