La Voulte-sur-Rhône (lagerstätte)
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The late Middle Jurassic
lagerstätte A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These f ...
at La Voulte-sur-Rhône, in the Ardèche region of southwestern
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...
, offers
paleontologists Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...
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 giv ...
s in the silty shale are symptoms of an
anoxic The term 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 diss ...
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 Beecher's Trilobite Bed is a Konservat-Lagerstätte of Late Ordovician (Caradoc) age located within the Frankfort Shale in Cleveland's Glen, Oneida County, New York, USA.Hunsrück Slate The Hunsrück () is a long, triangular, pronounced upland in Rhineland-Palatinate, Germany. It is bounded by the valleys of the Moselle-Saar (north-to-west), the Nahe (south), and the Rhine (east). It is continued by the Taunus mountains, past ...
, 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'' fauna (consisting of soft-bodied organisms which lived on the sea floor ( benthic) 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 preserved ...
s of pycnogonids ("sea-spiders"), the first find in
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
strata in an admittedly very patchy fossil record, were identified in 2007. A
coleoid Subclass Coleoidea, or Dibranchiata, is the grouping of cephalopods containing all the various taxa popularly thought of as "soft-bodied" or "shell-less" (i.e., octopuses, squid and cuttlefish). Unlike its extant sister group, Nautiloidea, whose ...
cephalopod (a single specimen of a small octopus) was described from La Voulte-sur-Rhône in 1982. The marine crocodile ''
Metriorhynchus ''Metriorhynchus'' is an extinct genus of marine crocodyliform that lived in the oceans during the Late Jurassic. The type species, ''M. brevirostris'' was named in 1829 as a species of ''Steneosaurus'' before being named as a separate genus by ...
'', 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 ...
crustaceans, thylacocephalans,
crinoid Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which are ...
s, and
ophiuroid Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...
s (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 The (; oc, Massís Central, ; literally ''"Central Massif"'') is a highland region in south-central France, consisting of mountains and plateaus. It covers about 15% of mainland France. Subject to volcanism that has subsided in the last 10,0 ...
.


References

{{DEFAULTSORT:La Voulte-sur-Rhone (lagerstatte) Jurassic System of Europe Callovian Stage Lagerstätten Paleontology in France