QR Les Martres-de-Veyre 3
The salt march
A testament to thermomineral activity
This vast parcel of land stands in stark contrast to the cultivated fields on its outskirts. It is covered with sparse vegetation, occupying the spaces left open by the rocky outcrops. No trees grow here.
This terrace bears witness to a geological episode in the history of the Allier. In the Quaternary period, the river, which was much wider than it is today, carved out a bed in the crystalline granite bedrock and left alluvial deposits of pebbles. On the salt marsh there are outcrops of granite, and others made up of pebbles hardened by a limestone cement, and others forming a veneer of travertine, a limestone rock formed by the emergence of thermomineral springs rich in calcium carbonate. Although there are no springs today, the travertine veneers bear witness to their former presence. On two occasions, work carried out at the end of the 19th century led to the appearance of bubbling springs whose water, at a temperature of around 16°C, was found to have a composition similar to that of the Petit Saladis. The most recent of these two springs, known as the Tixier spring, flowed for several months before drying up.
The Puccinellia distans
Even if it doesn’t appear in the open air, mineral water is omnipresent here at shallow depths. This is why the soil in this land is both salty and highly alkaline, causing the vegetation to have to adapt to such difficult conditions, excluding the species found in the surrounding area.
However, a small grass, the Puccinellia distans, has found the ideal conditions to grow and forms small patches between the rocky veneers. This halophilic species can be found on the coast and in continental salt marshes, particularly in Auvergne. It also thrives on roadsides that are heavily salted in winter.
- Salt marshes are vast, bare areas where the chemical make up of the soil and rocky outcrops make it difficult for plants to grow.
- The rocky outcrops are a prime habitat for mosses, lichens and rock plants such as Orpinium, which here punctuates the meadow with beautiful red patches.
- Outcrop of puddingstone with basalt pebbles.
- The Puccinellia distans (photographed here on the edge of the Grand Saladis) is a strict halophile that has largely colonised the salt marsh.