Discover France and Explore the Fossils & Geodiversity of Cerin in Marchamp, Department of Ain
- Wayne Munday
- Dec 5, 2025
- 4 min read
Sip back and discover France and explore the fossils and geodiversity of the picturesque hamlet of Cerin located on a limestone plateau above the Rhône Valley between Lyon and Geneva in the Ain Department of eastern France. Known for the Cerin Lagerstätte, a Konservat-Lagerstätte of global significance that preserves delicate organisms from a Late Jurassic lagoon dating back 153 million years. This fossil site is part of the Cerin Lithographic Limestone Formation that holds an exceptional preservation of fish, jellyfish, crocodilians, Horseshoe Crabs, pterosaurs and rare terrestrial plants. Linked paleogeographically to Bavaria’s Solnhofen Limestone, Cerin offers vital insights into the ancient Tethys Ocean and lagoon–reef complexes of the Kimmeridgian age in Europe. Today, the former quarry is protected as an Espace Naturel Sensible and visitors can explore the “Sentier des Carriers” trail and the Musée paléoécologique de Cerin.
Cerin is a tranquil hamlet located between Lyon and Geneva in the Marchamp commune of Ain Department in eastern France. Located on a limestone plateau above the Rhône Valley it is an ideal destination and gateway from which to explore the Jura Mountains. Renowned for the Cerin Lagerstätte found in the local fine limestone that was historically quarried for use in lithography and attracted scientific attention in the 1830s and 1840s by the likes of Victor Joseph de l'Isle Thiollière (1801 – 1859) who is credited with creating the first geological map of the Rhône department. Later excavations by academics such as Université Claude-Bernard Lyon 1 would lead to revealing the site’s true significance as a Konservat-Lagerstätte that has preserved soft tissues and delicate organisms in remarkable detail. The Cerin Lagerstätte tells a story of a Late Jurassic shallow tropical lagoon about 153 million years ago during the Late Kimmeridgian.
This former quarry is protected as one of forty natural heritage areas designated as Espace Naturel Sensible (ENS) and visitors can enjoy the 2 Km “Sentier des Carriers” or “Quarrymen’s Trail” leading to the outcrop and visit the open all year round Musée paléoécologique de Cerin to see many of the key fossils exhibited. Nearby attractions such as the Gorges de la Balme and Lac d’Armaille add limestone caverns, tranquil waters and Bugey culinary traditions to the visitor experience. Cerin is a compact, evocative destination that is scientifically significant and refreshingly off the beaten track.
The Cerin Lagerstätte was located on the western margin of the ancient Tethys Ocean and represents a Late Jurassic lagoon–reef complex that experienced periods of hypersalinity. The Cerin Lithographic Limestone Formation that holds the Cerin Lagerstätte sits within a broader paleogeographic framework in Europe that links it to other world-famous lithographic deposits including the Solnhofen Limestone of Bavaria best known for Archaeopteryx.
Deposited in calm, often anoxic waters in a semi-arid, tropical environment, the Cerin Lagerstätte records repeated cycles of flooding, drying, and occasional marine incursions that created finely laminated micritic sediments. The stratigraphy begins with thin, millimetre-scale laminated micritic limestones overlain by thicker lithographic limestone beds ranging from 5 to 25cm, often capped by microbial mats that contributed to exceptional fossil preservation. These ultrafine carbonate layers capture detailed evidence of oxygen fluctuations, salinity variations, storm events, and sedimentation dynamics within the lagoon. Periodic connections to the Tethys allowed marine fauna to enter and for terrestrial remains to be transported into the lagoon during storms.
Cerin's lagoonal deposits capture an extraordinary array of fish, including articulated specimens and actinopterygians such as semionotids, macrosemids, and pycnodontids like Gigacerina saemanni, Soleryon amicalis and Turboscinetes egertoni, alongside sharks and rays. Invertebrates are equally abundant, with horseshoe-crab relatives such as Mesolimulus walchii and the trackways of giant Kouphichnium limulid and Giant Turtles, echinoderms, and dasyclad algae including Clypeina jurassica.
Soft-bodied preservation is highlighted by exquisitely fossilised jellyfish, including Paraurelia cerinensis. Other vertebrate fossils extend beyond fish to reptiles and notably crocodilian relatives like Crocodilaemus robustus and pterosaurs such as the ctenochasmatoid Cycnorhamphus. Cerin’s restricted lagoon was a poor trap for large terrestrial vertebrates with the rarity of dinosaur bones found.
The Cerin Lagerstätte not only preserves marine and aquatic life but also terrestrial vegetation that fringed its lagoon margins. Fossilised plants and leaves, including Pteridospermales, Bennettitales, and cycads, indicate a warm, semi-arid coastal environment where vegetation adapted to periodic dryness and high sunlight. The presence of xerophytic features or specialised adaptations such as thickened leaves are evident meaning they evolved to survive in dry, arid, or water-limited environments. These features reduce water loss, store water, or help plants tolerate high sunlight and heat that reflects the local microclimates within the broader tropical setting of the southern Jura region.
The Cerin Lagerstätte offers a glimpse into Jurassic world frozen in limestone. From the delicate microbial-capped layers to swarms of fossilised jellyfish, articulated fishes, and ancient arthropod trackways, Cerin reveals how tranquil lagoonal sediments and microbial activity can preserve life in extraordinary detail making it a must-see destination for anyone curious about the natural history of the southern Jura Mountains.
