Discover France and Explore the Fossils and Geodiversity of Chablais region of the French Alps
- Wayne Munday
- Oct 29
- 4 min read
Sip back and discover France and explore the Chablais UNESCO Global Geopark, designated in 2015, spanning 50 Km from Thonon-les-Bains on the southern shore of Lake Geneva to the high passes near Morzine and Avoriaz, covering 870 km² of Haute-Savoie’s dramatic Alpine landscape. This geopark reveals 245 million years of Earth history, from Triassic and Jurassic carbonate deposition to the folding and stacking of limestone rocks into nappes during the Alpine Orogeny. The terrain bears the imprint of Pleistocene glaciation and notably the Rhône Glacier which carved deep U-shaped valleys, cirques and overdeepened basins now lakes like Lac de Montriond and Lac des Plagnes. The influence of karst processes upon Jurassic and Cretaceous limestones has further shaped the region, forming gorges, sinkholes and subterranean drainage networks at places like Gorges du Pont du Diable. Chablais also preserves a limited but valuable microfossil record of marine life including nummulites reflecting its Mesozoic and early Cenozoic shallow tropical seas. The region’s nummulitic limestones form the Nummulitique that acts as a natural filtration system responsible for the globally renowned mineral waters of Évian-les-Bains and Thonon-les-Bains. The geodiversity of Chablais creates a breathtaking landscape to experience and celebrate for its natural beauty, scientific significance and contribution to your own wellbeing.
At the heart of Haute-Savoie in the Auvergne-Rhône-Alpes region of south east France lies the Chablais UNESCO Global Geopark designated in 2015. Situated along the French –Swiss border the geopark stretches for approximately 50 kilometres from Thonon-les-Bains on the southern shore of Lake Geneva (Lac Léman) to the high mountain passes near Morzine and Avoriaz encompassing about 870 Km² of breathtaking Alpine terrain. This dramatic landscape of rugged limestone peaks, glacially carved valleys and crystal-clear lakes reveals over 245 million years of Earth’s geological history. The story of Chablais unfolds from the ancient seas of the Triassic and Jurassic periods, when carbonate sediments accumulated on the seafloor to the powerful Alpine Orogeny that folded and stacked these rocks into towering nappes. The region also displays striking karst formations and glacial features sculpted by groundwater dissolution and Pleistocene ice. Visitors can explore this region from the choice of the spa towns of Évian-les-Bains and Thonon-les-Bains or the medieval charm of Yvoire or the vibrant mountain resorts of Les Gets, Châtel and Morzine.
The Chablais region of the French Alps and especially the communes of Évian-les-Bains and Thonon-les-Bains are world-renowned for their sustainably sourced mineral waters for over 200 years. The distinctive Alpine geology and hydrology of this area has played an influential role in creating a mineral water regarded highly for its purity, clarity, mineral composition, taste and health properties. The surrounding porous and calcareous Nummulitique limestone combined with glacial deposits from the Pleistocene has created an exceptional natural filtration system for rainwater, ground water and snowmelt to percolate slowly through the rock over decades enriching the water with essential minerals such as calcium, magnesium, and bicarbonates. This prolonged underground journey of up to 15 years also protects the springs from surface contamination ensuring a consistently clean, crisp and refreshing taste free from contaminants and the naturally occurring minerals and low sodium concentrations has proven health benefits for hydration, metabolic balance and cardiovascular wellness.
The Chablais UNESCO Global Geopark in France preserves a microfossil record that offers a glimpse into ancient marine environments preceding the Alpine uplift, yet its overall fossil record is relatively limited. The region’s bedrock is dominated by marine sedimentary rocks, including Triassic dolomites, Jurassic limestones, Cretaceous marls and Paleogene nummulitic limestones. All of which had originally been deposited in the shallow, warm tropical seas of the ancient Tethys Ocean. These sediments favoured the preservation of marine invertebrates such as ammonites, bivalves, bryozoans and nummulites. However, the intense tectonic activity of the Alpine Orogeny, which began in the Late Cretaceous, profoundly altered these sediments. Rocks were folded, thrust and stacked into nappes exposing fossil-bearing layers to extreme pressure, shearing and metamorphism that often obliterated fragile remains. Later, Pleistocene glaciations reshaped the landscape, scouring valleys, transporting debris and further reducing the number of accessible fossil horizons. Consequently, while Chablais retains important evidence of its marine past but the combined effects of Alpine tectonics and glacial modification have significantly constrained the preservation of fossils.
Over 250 million years ago the region lay beneath the Tethys Sea where marine sediments rich in calcium carbonate laid down in a warm shallow tropical environment and gradually over time compressed to become the bedrock. In the Cretaceous Period there was narrowing and closing of the Tethys Sea and river sediments began to deposit the distinctive red limestones and marls or couches rouges that are visible in the valleys of Abondance and Brevon.
Then during the Paleogene Period nummulitic limestones were laid down in the region’s early Cenozoic marine environment. The nummulitic limestone in the Chablais region is part of a larger geological unit called the "Nummulitique". This term refers to the Paleocene–Eocene-aged sedimentary rocks containing abundant Nummulite fossils that are found across the Alpine foreland basin along the margins of the ancient Tethys Sea. Nummulites are large extinct marine foraminifera whose abundant calcareous shells were deposited after the extensive Mesozoic carbonate sequences. The Nummulitique records the final phases of shallow marine sedimentation before the Alpine Orogeny began to uplift and deform the region’s rocks.
During the Alpine Orogeny at beginning in the Late Cretaceous around 70 million years ago the convergence of the African and Eurasian tectonic plates compressed and deformed these once horizontal sedimentary limestone layers and thrusted them into massive nappes and folded them into a series of anticlines and synclines. Prominent examples, such as the the Mémises syncline and the Nappe de la Brèche and Préalpes Médianes Plastiques show prominent fold-and-thrust features.
Between approximately 2.6 million and 11,700 years ago, Pleistocene glaciations profoundly transformed the Chablais region, with the Rhône Glacier flowing from the high Alps into the surrounding valleys. This immense ice flow reshaped the landscape through glacial erosion and deposition, carving deep U-shaped valleys, sculpting cirques, and leaving behind moraines, erratic boulders, and overdeepened basins. Many of these glacially excavated basins now host the picturesque alpine lakes of Lac de Montriond and Lac des Plagnes in the Vallée d’Aulps. As the glaciers retreated, meltwater and rivers further reshaped the valley floors, forming fertile basins that now support towns and the region’s renowned mineral springs.
