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Discovering Switzerland and Exploring the Geodiversity of the Jura Mountains

The Jura Mountains straddle both Switzerland and France offering the explorer a stunning natural karst scenery where the combination of marine sedimentation, mountain building and glaciation have all played their part to influence the local geodiversity and fossil record. So, sip back and discover how this region was once submerged by the Tethys Sea during the Jurassic Period that not only created a platform of limestone, one of the four distinct geological units of this small country, but importantly preserved a moment in time that tells us a story of when sauropod and theropod dinosaurs roamed the tidal shores.


Creux du Van meaning "rocky hole" on the Jura Mountains - Image by Luca Pellegrini
Creux du Van meaning "rocky hole" on the Jura Mountains - Image by Luca Pellegrini

The term Jura originates from the early inhabitant's of the area known as the Gauls whose word’s jor or juria meant "forest" and the invading Roman's called the woodland of the mountains the juris.


Since the last glacial maximum (LGM) or ice age of the Pleistocene Epoch between 2.58 million – 11,800 years ago the combination of a westerly flow of a relatively mild and moist air from the Atlantic Ocean and local geology has helped to shaped the Jura Mountains creating an Alpine Forest ecosystem of hornbeam, beech, maples, firs, spruce and pine trees with both lowland and highland grass pastures.



The Jura Mountains lay mostly in Switzerland and form a natural border with France whose arc spans over 360 Km from the rivers of the Aare and Rhine in the northeast crossing the Franco-Swiss border from the Rhône River to the Rhine in the southwest.



One of the best ways to experience the Jura Mountains is to consider walking all 16 stages of the 320 Km national long-distance Jura Crest Trail described as an easy walking wanderweg between Zurich and Genève.


Youtube Video : Switzerland's Secret Mountain Range | The Jura


The highest peaks of the Jura mountains are in France with the Crêt de la Neige (1,720 m – 46.27250°N / 5.94361°E) and Le Reculet (1,718 meters - 46.25667°N / 5.93000°E) followed by Mount Tendre and La Dôle in Switzerland.


The Jura Mountains cover about 10% of Switzerland and in the southern foothills are some of the country's largest lakes including Lake Geneva, Lake Bienne and Lake Neuchâtel are found. The Jura Mountains fall within 8 of the 26 cantons of Switzerland that make up the Swiss Confederation including Geneva, Vaud, Neuchâtel, Bern, Jura, Solothurn, Basel-Landschaft and Aargau fall and the eastern French region of Bourgogne–Franche-Comté.


Folding Jurassic Period strata at Chapeau de gendarme on the Jura Mountains - Image by WikiMedia
Folding Jurassic Period strata at Chapeau de gendarme on the Jura Mountains - Image by WikiMedia

In 1795 the German naturalist and scientific explorer Alexander von Humboldt used the term “Jura Kalkstein” or Jura Limestone to designate the carbonate sedimentary deposits of the Jura though it was not until 1829 when Alexandre Brongniart a French mineralogist, geologist, and naturalist used the term “Terrains Jurassiques” to describe the Jura Kalkstein as Jurassic strata.


In 1832 the German geologist Leopold von Buch described the subdivisions of Jurassic Period in terms of the Early, Mid and Late Epochs based on the folds of limestone in the Jura mountains. This research nearly 200 years on still underpins our geological understanding of the Jurassic Period dating between 201.4 – 143.1 million years ago.



During the Jurassic Period, Switzerland was covered by Tethys Sea a tropical body of salty water. This marine environment created one of four distinct geological units of Switzerland consisting of a large platform area of sedimentary limestones, marls, clays, anhydrite and gypsum.


Walkerssk
Depiction of the warm Tethys Sea - Image by Walkerssk

As the Alps formed during the Alpine Orogeny (between 65 and 2.5 million years ago) from the collision between the African and the Eurasian tectonic plates. The sedimentary rocks of northern platform were put under immense pressure and subsequently detached from the underlying bedrock and began to fold and fault.


The Jura Mountains today are a complex fold-and-thrust belt with many faults that gives the area its characteristic appearance of a rugged terrain of anticlines (upward-arching folds) and synclines (downward-arching folds).


The Entre-Roches Gorge in the Jura Mountains - Image by JGS25
The Entre-Roches Gorge in the Jura Mountains - Image by JGS25

Both above through erosion and below the surface the karst scenery carved out from the limestone rock of the Jura Mountains has created extensive cave systems, underground rivers, and dramatic limestone cliffs. Such places include the Entre-Roches gorge and also the Grotto of Réclère located west of Porrentruy. Discovered in 1886 this 1.5 Km underground cave system also has Switzerland largest stalagmite called the Grand Dôme.


The Grand Dome (Stalagmite) at Caves of RÉCLÈRE - Image by Thomas Bresson
The Grand Dome (Stalagmite) at Caves of RÉCLÈRE - Image by Thomas Bresson
Dinosaurs of the Jura Mountains

The first published fossil record of Swiss dinosaurs’ dates back to the 18th and 19th century when several palaeontological monographs were published by eminent scientists including: Ludwig Rütimeyer a Swiss palaeozoologist and geographer who found a giant reptile from the Late Triassic Upper Norian red-beds of the Trossingen Formation, formerly the Knollenmergel famous for its prosauropod dinosaurs the smaller ancestor to the later and larger sauropod dinosaurs; Swiss geologist Jean-Baptiste Greppin described the first sauropod found in the Upper Jurassic Reuchenette Formation in a limestone quarry in the Basse Montagne, near the city of Moutier. And Swiss palaeontologist and stratigraphist Charles Louis Perceval de Loriol who described the fossils found on the Jura Mountains.



In recent times one of the most significant fossil finds was in 1987 when Europe’s largest trackway of over 400 quadrupedal dinosaurs footprints was discovered in the Lommiswil Quarry near Solothurn in Switzerland.


In 2002 during the construction of the Transjurane highway A16 connecting Biel in the Canton of Bern to the Swiss border in Delle-Boncourt in the Canton of Jura a now internationally important area of Late Jurassic sauropod and theropod dinosaur footprints were discovered.


Above : Dinosaur footprints from Courtedoux in the Jura Mountains - Images by Tobias1984 and Jurassic & Dinotec


Established in February 2000 an organisation known as Paléontologie A16 based in Porrentruy and part of the Office of Culture of the Republic and Canton of Jura started the mission to safeguard, document, analyse, study and archive the paleontological heritage destined to be destroyed by the construction of the A16 Transjurane motorway.


The JURASSICA museum in Porrentruy presents a permanent fossil collection from the Jura that tells a story rich in biodiversity of coral reefs, ammonites, fish and turtles whilst dinosaurs wandered the shoreline.


The JURASSICA Museum in Porrentruy - Image by JURASSICA
The JURASSICA Museum in Porrentruy - Image by JURASSICA

Many of the fossil discoveries are from the Reuchenette Formation in the Courtedoux region date back to the Kimmeridgian Age (154.8 – 149.2 million years ago) which was the second of the three ages within the Late Jurassic Epoch preceded by the Oxfordian Age and succeeded by the Tithonian Age.


The Jura Mountain fossil record includes thousands of dinosaur footprints or ichnites found the fine carbonate sediments of the Corbis Limestone laid down in a once flat tidal coastal marine and tropical paleoenvironment on the shores of the Tethys Sea. 


Many of the dinosaur footprints are tridactyl or having three toes belonging to two co-existing apex predators known as Megalosauripus transjuranicus and the larger Jurabrontes curtedulensis that stood around 10-12 metres tall.


Dinosaurs at JURASSIC - Image by Stéphane Schmutz
Dinosaurs at JURASSIC - Image by Stéphane Schmutz

These Limestone sediments are sandwiched between the Upper and Lower Kimmeridgian Virgula Marls and Banné respectively that are dominated by an extinct family of turtles known as Plesiochelyidae and well as other marine vertebrates.


Brontopodus footprints at the village of Plagne Image by Patrick Dumas

Then in 2009 the largest known European Sauropod dinosaur footprints and a 110 step trackway at over 155 meters was found in the French village of Plagne in the Jura Mountains.


Following a period of study scientists from the Laboratoire de Géologie de Lyon (CNRS / ENS de Lyon / Claude Bernard Lyon 1 University), the Laboratoire Magmas et Volcans (CNRS / Université Clermont Auvergne / Université Jean Monnet / IRD), and the Pterosaur Beach Museum they concluded that the trackway dated to the Early Tithonian Age (149.2 - 143.1 million years).


The dinosaur that made these tracks would have been over 35 meters in length and weighing over 35 tons.


The footprints rather than the species of this long necked herbivorous sauropod dinosaur was named Brontopodus plagnensis. The impression of the footprints show five elliptical toe marks and the feet span between 94 - 103 cm. This gigantic dinosaur would have moved or rather lumbered at steady 4 km/h and each stride was roughly 2.80 meters in length. Other tracks in the same area are described as belonging to Megalosauripus a much smaller bipedal theropod dinosaur.


The Jura Mountains are traditionally known for their outdoor activities and tranquil panoramas all year round. But if you want to truly walk in the land of giant dinosaurs this is most certainly the place to visit during the summer when the trackways are clear and museums conserving these paleontological treasures are open.



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