Discover France and Explore the Fossils & Geodiversity of the Aurillac Basin in Cantal Department

Sip back and discover France and explore the fossils and geodiversity of Aurillac the historic prefecture of the Cantal department in south-central France located in the Aurillac Basin at the foot of the Monts du Cantal. The town is surrounded by the Parc Naturel Régional des Volcans d’Auvergne where visitors can encounter glacial cirques, lava domes, and sweeping views from Puy Mary and Plomb du Cantal. Geologically, the basin rests on the Variscan crystalline basement and preserves Oligocene lake sediments with limestones, marls, dolomites, and diatomites, including fossils like Potamides lamarcki, though the fossil record is fragmentary due to Miocene volcanism from the Cantal stratovolcano which built planèzes plateaus, trachyte and phonolite domes and pyroclastic breccias. Quaternary glacial water deposits in the Cère Valley host larger mammal remains as well as the Oligocene fossil assemblages of the nearby Quercy Phosphorites. Aurillac is well connected by train, road, and flights and is an ideal gateway to explore the Massif Central’s geodiversity.

The Cheylade valley and the north face of the Puy Mary - Image by Pline

Aurillac is the historic prefecture of the Cantal department in south-central France and sits sheltered in the Aurillac Basin at the foot of the Monts du Cantal. Aurillac’s heritage endures in landmarks such as the 9th-century Benedictine Abbey Church of St. Gerald the birthplace of Gerbert the first Frenchman to become Pope Sylvester II in 999. Additionally is Château Saint-Étienne which is home to the Museum of Volcanoes and the Musée d’Art et d’Archéologie. Aurillac is surrounded by the Parc Naturel Régional des Volcans d’Auvergne where visitor immerse themselves in the outdoors hiking the trails to see the glacial cirques, lava domes and panoramic viewpoints atop the Grand Site de France of Puy Mary (1,787m) spanning a diameter of 70 km and an area of 2,700 Km² making it Europe's largest stratovolcano and Plomb du Cantal the highest point of the Monts du Canta (1,855 m). Aurillac is known for its cultural vibrancy, most notably the International Street Theatre Festival held each August. Aurillac serves as an ideal base for exploring the Massif Central and is well connected by regional trains, flights from Paris, and major road links such as the N122.

The Aurillac Basin in south-central France presents a compelling geological narrative shaped by ancient crystalline bedrock, Oligocene lake sediments, and the immense volcanic influence of the Cantal stratovolcano. Located at the foot of the Cantal Mountains within the Massif Central, this low-lying depression developed between volcanic plateaus, glacially carved U-shaped valleys, and the remnants of Europe’s largest stratovolcano. While it is sometimes associated with France’s classic fossil regions, the basin is defined less by abundant fossil deposits and more by its dynamic volcanic and tectonic history. Here, successive eruptions of the Cantal volcano have partially buried, altered, or preserved earlier sedimentary environments.

Visit the Fossil Coast Drinks Shop

The Aurillac Basin is not only a cultural hub but also a geological crossroads. Its volcanic history, fragmentary fossil record, and dramatic scenery connects visitors to the wider Massif Central, a region defined by tectonic upheaval, glaciation, and volcanism. Exploring Aurillac means stepping into a story that stretches back hundreds of millions of years, while also linking to nearby destinations such as the Quercy Phosphorites fossil sites, the UNESCO‑listed Chaîne des Puys volcanoes near Clermont‑Ferrand, and the Parc Naturel Régional des Volcans d’Auvergne.

The foundation of the Aurillac Basin lies in the Variscan, or Hercynian, crystalline basement, a bedrock of granites and gneisses formed more than 300 million years ago during a mountain‑building event that shaped much of western Europe. This ancient basement provided the stable platform upon which younger sedimentary and volcanic layers accumulated.

During the Oligocene epoch, between 34 and 23 million years ago, the basin hosted a series of intracontinental lakes. These lakes deposited limestones, marls, dolomites, and diatomites, creating a detailed record of changing environments. Fossils such as Potamides lamarcki, a gastropod adapted to brackish waters and reveal an ecosystem shaped by fluctuating salinity and evaporation. Nearby sites such as Murat preserve thick diatomite deposits composed of silica‑rich algal remains. These Oligocene lake beds provide a rare glimpse into pre‑volcanic landscapes, long before the Cantal stratovolcano rose to dominate the region.

The volcanic transformation began around 13 million years ago, when the Cantal stratovolcano erupted repeatedly over millions of years, eventually reaching a height of more than 3,000 meters. Its eruptions buried vast areas of the earlier sedimentary landscape beneath thick lava flows, ash deposits, and debris‑avalanche breccias. Broad basaltic flows spread outward to form the distinctive planèzes, flat‑topped volcanic plateaus that radiate from the ancient center. More evolved magmas produced trachyandesite, trachyte, and phonolite domes, shaping the rugged skyline that still defines the Monts du Cantal today.

Explosive eruptions generated chaotic pyroclastic breccias that filled valleys, while rare volcanic ash layers preserved fossilized plant roots, offering snapshots of pioneer ecosystems colonising freshly emplaced volcanic surfaces.

This immense volcanic construction transformed the Aurillac Basin so profoundly that most earlier Oligocene sediments were buried, altered, or eroded away. Nineteenth‑century geologists recorded lake formed limestones around Aurillac, but modern studies reveal that these deposits survive only in limited, discontinuous exposures. The volcanic history destroyed much of the basin’s original sedimentary record, drastically reducing the potential for preserving extensive fossiliferous horizons.

Although Aurillac is not a classic fossil destination its does hold a fragmentary fossil record. Small mammal finds from sites such as Vialenc known for its abundant and diverse rodent fossils include glirid and eomyid rodents. Scattered localities in the Cantal region have produced additional Cenozoic material, including rhinoceros remains, though these are not typical of Aurillac itself. More substantial paleontological evidence appears in the Quaternary fluvio‑glacial sediments that fill the Cère Valley. Here, thick sands and clays deposited during Pleistocene glaciation contain large mammal fossils, archaeological materials, and siliceous pebbles later used for prehistoric toolmaking in regions such as the Dordogne.

The scarcity of continuous fossil bearing sedimentary horizons reflects the dynamic geological evolution of the Massif Central, where volcanism, uplift, erosion, and repeated glaciation buried, reworked, or removed earlier strata. This contrasts sharply with more stable Oligocene basins such as the Quercy Phosphorites, where abundant assemblages of mammals, birds, and reptiles are preserved in phosphatic cave deposits. For travellers interested in palaeontology, Aurillac offers insight into how volcanism can obscure fossil records, while nearby Quercy provides the opportunity to see one of Europe’s richest fossil sites.