The 330-320 Million-Year-Old Tranchee des Malecots (Chaudefonds-sur-Layon, South of the Armorican Massif, France): a Rare Geoheritage Site Containing In Situ Palaeobotanical Remains

A disused quarry in the southern part of the Amorican Massif (northwestern France) known locally as the 'Tranchee des Malecots' lies within the 'Corniche Angevine' located on the western edge of the 'Val de Loire' UNESCO World Heritage Site. This quarry exposes Serpukhovian-age (330-320 Ma) volcanic ashes containing in situ remains of arborescent lycopsids and is one of the few places in the world where very early coal swamp plants can be seen in their original place of growth. Because the geology and palaeobotany here relate to coal mining, which historically underpinned the economic development of the area, the site is of considerable local cultural interest. The site was first described in the early 1930s, and its reinvestigation has shown occurrences of lycopsid remains identified as stems and branches of Lepidodendron veltheimii and Lepidodendron cf. nathorstii, slender axes with lateral branches of uncertain affinities, Cyperites bicarinatus leaves and Stigmaria ficoides rhizophores. A pictorial reconstruction of the trees is presented. Since the first description of the site, a combination of natural erosion and human damage has meant that fewer of the trees are now visible. In 2016, we used photogrammetry to develop a digital representation of the site and its fossil remains to help in the development of a long-term geoconservation strategy. Modern vegetation had recently been removed from the outcrop showing more stems, but other remains have disappeared. This highlights the value of photogrammetry to allow continued knowledge and preservation of this internationally important example of geoheritage.

Automated summary

A disused quarry in the Amorican Massif in France has exposed early coal swamp plants and has significant cultural and geological value. However, due to erosion and human damage, fewer of the trees are now visible. The use of photogrammetry has allowed for the digital preservation of this important geoheritage site.