The late Middle Jurassic

lagerstätte A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...

at La Voulte-sur-Rhône, in the

Ardèche Ardèche (; , ; ) is a Departments of France, department in Auvergne-Rhône-Alpes, Southeastern France. It is named after the river Ardèche (river), Ardèche and had a population of 328,278 as of 2019.France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

, offers paleontologists an outstanding view of an undisturbed paleoecosystem that was preserved in fine detail as organisms died at the site and settled to the bottom of a shallow epicontinental sea, with a folded floor that in places exceeded 200 m at this site. The site preserves a marine system of the Lower Callovian stage, a little over 160 mya. The sequence is exposed in a series of quarries at La Boissine, west of the village of La Voulte-sur-Rhône.

Iron pyrite The mineral pyrite ( ), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...

s in the silty shale are symptoms of an

anoxic Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved ox ...

environment. The site was recognized among French paleontologists from the mid-nineteenth century for its finely detailed fossils.

Preservation

Some soft parts of organisms are preserved as phosphatised concretions, in exceptional cases down to cellular details, ''e.g.'' retinal structures in the eyes of conchyliocarid crustacea. Apart from Beecher's Trilobite Bed and the Hunsrück Slate, La Voulte-sur-Rhône is the only other locality where extensive pyritization of soft parts occurs. see page 41 However, pyritisation is not the only preservation pathway; several stages of mineralization (originally phosphate followed by calcite or gypsum, then pyrite and finally galena) are seen, each successive mineralization event degrades the detail preserved, with only gross morphological features preserved in the most advanced stages. "La Voulte-sur-Rhone" by Sarah Joomun, Dept. of Earth Science, Bristol University
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Fauna and flora

The fauna preserved can be broadly divided into the ''

allochthonous River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts.Angelier ...

'' fauna (consisting of soft-bodied organisms which lived on the sea floor (

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 the Ancient Greek word (), meaning "the depths". ...

) or swam freely just above it ( nektobenthic)) and the ''in-situ'' mortality horizon. The allochthonous fauna contains rare and well-preserved organisms.

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s of pycnogonids ("sea-spiders"), the first find in

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

strata in an admittedly very patchy fossil record, were identified in 2007. A

coleoid Coleoidea or Dibranchiata is one of the two subclasses of cephalopod molluscs containing all the various taxa popularly thought of as "soft-bodied" or "shell-less" (i.e. octopus, squid and cuttlefish). Unlike its extant sister group Nautiloide ...

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

(a single specimen of a small octopus) was described from La Voulte-sur-Rhône in 1982. The marine crocodile '' Metriorhynchus'', fish, decapod,

mysid Mysida is an order of small, shrimp-like crustaceans in the malacostracan superorder Peracarida. Their common name opossum shrimps stems from the presence of a brood pouch or "marsupium" in females. The fact that the larvae are reared in thi ...

crustaceans, thylacocephalans,

crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...

s, and ophiuroids (most commonly '' Ophiopinna elegans'') are also to be found. The ''in situ'' mortality horizon consists of abundant pavements of the bivalve '' Bositra buchi'' and trace fossils of suspected worm burrows. Two specimens of plants suggest that a shoreline was not far distant, represented today by France's Massif Central.

References

{{DEFAULTSORT:Voulte sur-Rhône (lagerstätte), La Jurassic System of Europe Callovian Stage Lagerstätten Paleontology in France