The Géoparc de Haute-Provence was designated in 2015 by UNESCO and is the largest in France. Among the Geoparks' 18 fossil and geological sites dating back over 300 million years is the Lower Jurassic Ammonite Wall or Dalle à ammonites of Digne-Les-Bains.
In February 2002, the French Government for the first time recognised in law the value and benefit of geological heritage across the country including the Digne-Les-Bains Geological Reserve.
The French law stated,
"The inventory of natural heritage is set up for the entire national territory of France. A natural inventory encompasses the inventory of the richness of ecologic, faunistic, floristic, geologic, mineralogical, and paleontological richness. It is also defining that the inventory is conducted under the scientific responsibility of the National Museum of Natural History of France"
The Ammonite Wall of Digne-Les-Bains (44° 07' 10'' N 006° 14' 03'' E) is a 350,000 square meter limestone wall exposing a biohorizon and best exposure in Europe of over 1,550 ammonites predominantly of the species Coroniceras multicostatum.
This region's paleontological heritage has always been part of many people’s childhood and nowadays their livelihood. The Ammonite Wall has over 20,000 visitors a year.
In 2022, the Ammonite Wall of Digne-Les-Bains was named among the “First 100 Geological Heritage Sites” designated by the International Union of Geological Sciences (IUGS).
The Haute-Provence administrative capital of Digne-Les-Bains is roughly 150 Km from Nice, Marseille, and Grenoble. This once impoverished agricultural area nowadays benefits as a UNESCO Global Geopark and a popular destination for those interested in artisan food, drink, outdoor activities, culture as well as its natural environment, and of course, the fossils.
Before we dig into the Ammonite Wall there are several other interesting places near to Digne-Les-Bains that should be explored because they cross multiple geological and fossil records.
Less than a 30-minute drive along the D900A and D103 north from Digne-Les-Bains is the commune of La Robine-sur-Galabre.
At the Ravin de Bélier car park is the start of the Ichthyosaur Trail. A 90-minute 4 Km easy-going round trip taking in an open-air museum preserving the fossil remains of a 4.3-meter Ichthyosaur (“The Ichthyosaur of Robine”) discovered in the 1970s and dated from183 million years ago.
Less than an hour's drive from Digne-Les-Bains south along the meandering "Route Napoléon" of the N85 Autoroute is the ancient gated commune of Castellane situated on the banks of the river Verdon.
Before reaching Castellane and your visit to the permanent "Mermaids and Fossils" ("Sirènes et fossiles") exhibition at the Maison Nature & Patrimoines it's recommended to make two diversions.
The first diversion is to have a coffee at a café in the small elegant market town of Barrême located midway between Digne-Les-Bains and Castellane. This will prepare you for your next destination - more later.
The commune of Barrême is especially known for its pain d’ammonite (“Ammonite Bread”) found in local artisan boulangeries and also for the distillation of the much sort after “Lavender Barrême” whose floral aromas and essential oils that are reportedly valued as the most relaxing and therapeutic of all lavenders.
Barrême was the inspiration for the naming of the Barremian Stage by the French geologist and paleontologist Henry Coquand (1813 -1881) who was also the founder of the Muséum d'Aix in Aix-en-Provence.
The Barremian Age was the fourth of six ages of the Early Cretaceous Epoch 130.8 – 126.3 million years ago and marks the first appearance of the ammonite groups Taveraidiscus hugii and Avramisdiscus vandeckii.
Before travelling onwards to Castellane there is a second diversion and a small matter of hiking the Sirenian Trail where you can see the Mermaids up close.
Heading back on to the N85 Autoroute towards the Col des Lèques car park. This is the starting point for a 4 km family-friendly round trip that leads you up into the Verdon Mountains to a fossil site conserving the slow, passive, and herbivorous mammals known as Sirenians.
These animals lived in the surrounding tropical and sub-tropical waters at the time. Of the five living or extant species of Sirenians is the dugong and manatees, the Sirenians are known collectively as "sea cows".
The Haute-Provence UNESCO Global Geopark is made up of sedimentary rocks dating from the fifth of six stages of the Carboniferous Period known as the Stephanian Stage dated from 308 million years ago until the present day.
The geology of the region is complex with major unconformities, Mesozoic Tethyan rifting, and orogenic or mountain-building events behind the formation of the Provencal Mountain Chain and the Alpine Chains.
At the time when the foundations of the Ammonite Wall were forming a large area of Western Europe was under the Tethys Ocean.
Ammonites are perhaps the most widely known fossil, possessing the typically ribbed spiral shell and an ammonite was the inspiration for the Fossil Coast Drinks Co brand.
Ammonites were ubiquitous marine living shelled cephalopods that became extinct at the end of the Cretaceous some 66 million years ago.
Because of the speed and diversity of ammonite evolution, they have since the 1850s been used as a stratigraphic fossil marker to correlate the arrangement, succession, origin, composition, and distribution of strata around the world. This technique was pioneered by German geologists and paleontologists Friedrich Quenstedt and Albert Oppel.
The limestone exposure at Digne-Les-Bains has the best biohorizon of the species Coroniceras multicostatum from the Sinemurian Age (199.3 - 190.8 million years ago).
This stage is the second of the four ages of the Early Jurassic Epoch preceded by the Hettangian Age and succeeded by the Pliensbachian Age.
The Sinemurian Stage was named by French paleontologist Alcide Dessalines d’ Orbigny (1842–1851) after the town of Semur-en-Auxois. This was an ancient Roman town called Sinemurum Briennense castrum located in the Cote d’Or department in the Burgundy region of east-central France.
This area is also well known for its fossiliferous limestones and ammonites.
The Global Boundary Stratotype Section and Point (GSSP) or the global stratigraphy reference point for both the lower and upper boundary for the Sinemurian Age are found in England on the coastal exposures of East Quantoxhead near the town of Watchet in West Somerset and Wine Haven, near Robin Hood's Bay, Yorkshire, England.
Both of these boundaries are marked by a striking change in ammonite species as well as having at least six major ammonite biozones recognised between the Lower and Upper Sinemurian.
La dalle à ammonites - UNESCO Géoparc de Haute-Provence
The Lower Jurassic limestone of the Ammonite Wall of Digne-Les-Bains has a 60° gradient today. The uplift, folds, and faults of this region known locally as the Digne nappe were created by the tectonic deformations of the Alpine Orogeny between 65 and 2.5 million years ago and is active today.
The ammonite shells of the Ammonite Wall indicate that they were transported, deposited, and accumulated in a marine environment. The ammonites form a shell bed or more specifically a lumachella. Given the rock is limestone the deposition zone indicates a marine shelf environment enabling the formation of limestone.