The Dalle à ammonites (or Dalle aux ammonites) at

Digne-les-Bains Digne-les-Bains (; Occitan: ''Dinha dei Banhs''), or simply and historically Digne (''Dinha'' in the classical norm or ''Digno'' in the Mistralian norm), is the prefecture of the Alpes-de-Haute-Provence department in the Provence-Alpes-Cô ...

(

Alpes-de-Haute-Provence Alpes-de-Haute-Provence or sometimes abbreviated as AHP (; oc, Aups d'Auta Provença; ) is a department in the Provence-Alpes-Côte d'Azur region of France, bordering Alpes-Maritimes and Italy to the east, Var to the south, Vaucluse to the west ...

) is a remarkable natural site consisting of a rock strata bearing a large number of fossilized

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

s. This site is located approximately 1.5 km south of

from

Barles Barles () is a commune in the Alpes-de-Haute-Provence department in the Provence-Alpes-Côte d'Azur region of south-eastern France. The inhabitants of the commune are known as ''Barlatans'' or ''Barlatanes'' in French. Geography The village is l ...

road. It is part of the Géologique de Haute-Provence National Nature Reserve. The

slab Slab or SLAB may refer to: Physical materials * Concrete slab, a flat concrete plate used in construction * Stone slab, a flat stone used in construction * Slab (casting), a length of metal * Slab (geology), that portion of a tectonic plate that i ...

, inclined at 60°, is made of grey limestone. It bears around 1 500

s, 90% of which belonging to the species '' Coroniceras multicostatum'', dating from the

Sinemurian In the geologic timescale, the Sinemurian is an age and stage in the Early or Lower Jurassic Epoch or Series. It spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago). The Sinemurian is preceded by the Hettangian and is ...

(

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

). Those ammonites can attain a diameter of 70 cm.

Nautiloid Nautiloids are a group of marine cephalopods ( Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species ...

belemnite Belemnitida (or the belemnite) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are, from the arms-most to ...

s, '' Pecten'' seashells and other

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

s can also be found in the deposit. The deposit thickness is estimated to be 20 cm, deposited over a 100 000-year period.

Slab history

As well known as it is, the slab wasn't known until recently :

Alcide d'Orbigny Alcide Charles Victor Marie Dessalines d'Orbigny (6 September 1802 – 30 June 1857) was a French naturalist who made major contributions in many areas, including zoology (including malacology), palaeontology, geology, archaeology and anthrop ...

, who prospected the area in the middle of the

XIX century The 19th (nineteenth) century began on 1 January 1801 ( MDCCCI), and ended on 31 December 1900 ( MCM). The 19th century was the ninth century of the 2nd millennium. The 19th century was characterized by vast social upheaval. Slavery was abolish ...

, doesn't mention it. Geologists studying the

ichthyosaur Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...

remains near the site only mentions numerous species of

s and other

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

s. The dalle is thought to have been partially unearthed for the first time in June 1941, during road works on what is now the D 900A. In 1979, before the establishment of the Géologique de Haute-Provence National Nature Reserve, earthworks began to uncover the slab and unearthed 600 ammonites over 160 m². Until 1994 only 200 m² were visible. After this date, the Géologique de Haute-Provence National Nature Reserve took the task of clearing an additional 150 m2 to attain a total area of 350 m². The 160 m² already unearthed in 1992 of the slab were molded in 1992 by the geological reserve for the city of

Kamaishi is a city located on the Sanriku rias coast in Iwate Prefecture, Japan. , the city had an estimated population of 32,609, and a population density of 74 persons per km2, in 16,230 households. The total area of the city is Geography Kamaishi is ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

(who desired to buy the original). The mold was realized in 30 parts, which were sent and reassembled in Japan.

Geological aspect

Similar sites

An almost horizontal

Ammonoidea Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttle ...

slab, from the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

or the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

, is located below Fressac bridge over the Conturby river in

Gard Gard () is a department in Southern France, located in the region of Occitanie. It had a population of 748,437 as of 2019;Alpine orogeny. The Dignes-les-Bains area is located in the French

Prealps The Alpine foothills, or Prealps (german: Voralpen; french: Préalpes; it, Prealpi; ), may refer generally to any foothills at the base of the Alps in Europe. They are the transition zone between the High Alps and the Swiss Plateau and the Bavar ...

, in the Dauphinois geological facies. It bears the traces of the oceanisation preceding the orogeny beginning. The

Alps The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...

were erected in several phases, after a

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

happened in the paleo-ocean Tethys. The Dalle à ammonites, as well as other sites in the area, are witnesses of the first step of this process, and of what was life in this ocean before the apparition of the mountains. They bring paleontological context for the understanding of paleoenvironments and period conditions.

Paleontological analysis

The fossils aspect helps to understand the

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...

process. The good conservation of the shells give informations over the marine dynamism responsible for the deposit conditions : an hectic environment, like a beach or a coast, were the waves actions were strongly felt, with a tendency to break the shells, leading to fragmentary deposits, settled as ''

falun Falun () is a city and the seat of Falun Municipality in Dalarna County, Sweden, with 37,291 inhabitants in 2010. It is also the capital of Dalarna County. Falun forms, together with Borlänge, a metropolitan area with just over 100,000 inhabita ...

s'' or '' lumachella''. The majority of the fossils on the slab are still almost complete, which lead to the hypothesis of a milder environment, deeper, and better preserved. Moreover, this deposit was effected over the

carbonate compensation depth Carbonate compensation depth (CCD) is the depth in the oceans below which the rate of supply of calcite ( calcium carbonate) lags behind the rate of solvation, such that no calcite is preserved. Shells of animals therefore dissolve and carbonate ...

, and hence at an average depth. The tapophenosis analysis, as well as the position of the shells, lead to the conclusion that the Dalle à ammonites was an accumulation facies : a large number of dead animals were carried by weak marine currents, towards their deposit site. Traces of

bioturbation Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a pr ...

can be attributed to the

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

fauna, such as scavenger worms, who thrived in this biotope. Image:Dall Ammon-8.jpg, Fossil-bearing strata Image:Dall Ammon-7.jpg, Inclination, from the South Image:Dall Ammon-6.jpg, Inclination, from the North Image:Dalle à ammonites2.JPG, Détails Image:Dall Ammon-2.jpg, Details Image:Dall Ammon-4.jpg, Details Image:Dall Ammon-5.jpg, Details

References

External links

Réserve géologique de Haute Provence

Livret-Guide d'excursion géologique, congrès de l'Association des paléontologues français, 3-5 Mai 2007

Geography of Alpes-de-Haute-Provence Tourist attractions in Alpes-de-Haute-Provence Geologic formations of France Jurassic Europe Sinemurian Fossiliferous stratigraphic units of Europe Paleontology in France Alpes-de-Haute-Provence