The Saint-Chinian Formation is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

composed of shales with limestone inclusions, dating from the

Lower Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The ...

(

Tremadocian The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from to million years ago. The base of the Tremadocian is defined as the first appearance of the ...

). It is one of the six geological formations from the Saint-Chinian Cambro-

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

basin, comprising, from the most ancient to the most recent : La Dentelle Formation, Saint-Chinian Formation, La Maurerie Formation, Cluse de l'Orb Formation and Setso member, Foulon Formation and Landeyran Formation. This formation outcrops on the southern flanks of the

Montagne Noire The Montagne Noire ( oc, Montanha Negra, known as the 'Black Mountain' in English) is a mountain range in central southern France. It is located at the southwestern end of the Massif Central at the juncture of the Tarn, Hérault and Aude departm ...

in Southern France.. The formation received its name from the small city of

Saint-Chinian Saint-Chinian (; oc, Sanch Inhan) is a commune in the Hérault department in the Occitanie region in southern France. The town was the birthplace of the great tenor Agustarello Affre (1858–1931). He is commemorated by a plaque on the house ...

, a

commune A commune is an alternative term for an intentional community. Commune or comună or comune or other derivations may also refer to: Administrative-territorial entities * Commune (administrative division), a municipality or township ** Communes of ...

located in the

Hérault Hérault (; oc, Erau, ) is a department of the region of Occitania, Southern France. Named after the Hérault River, its prefecture is Montpellier. It had a population of 1,175,623 in 2019.department Department may refer to: * Departmentalization, division of a larger organization into parts with specific responsibility Government and military *Department (administrative division), a geographical and administrative division within a country, ...

Occitania Occitania ( oc, Occitània , , or ) is the historical region in Western Europe, Western and Southern Europe where the Occitan language, Occitan language was historically spoken and where it is sometimes still used as a second language. This ...

. It is dated from the biostratigraphic sub-zone characterized by Taihungshania miqueli and Asaphelina barroisi berardi.

Paleoenvironment

The thin nature of the silico-clastics deposits, the presence of slump, combined with a trilobite fauna dominated by members of the

Asaphidae Asaphidae is a family of asaphid trilobites. Although the first genera originate in Upper Cambrian marine strata, the family becomes the most widely distributed and most species-rich trilobite family during the Ordovician. 754 species assigne ...

family indicates a marine environment of external distal platform.

Paleofauna

Shales of the Saint-Chinian Formation bears in certain areas accumulations of phosphated

nodules Nodule may refer to: *Nodule (geology), a small rock or mineral cluster *Manganese nodule, a metallic concretion found on the seafloor *Nodule (medicine), a small aggregation of cells *Root nodule Root nodules are found on the roots of plants, p ...

, each potentially bearing a trilobite. Those are the so-called "''schistes à gateaux''".. *

Trilobites Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

: *:Members from the

Asaphida Asaphida is a large, morphologically diverse order of trilobites found in marine strata dated from the Middle Cambrian until their extinction during the Silurian. Asaphida contains six superfamilies (Anomocaroidea, Asaphoidea, Cyclopygoidea, ...

order and the

family are commons : ** '' Asaphelina barroisi barroisi'', ** '' Asaphelina barroisi berardi'', ** '' Niobella ligneresi'', ** '' Paramegalaspis immarginata'', ** '' Asaphellus frequens'', ** '' Taihungshania miqueli'', ** ''

Ampyx priscus ''Ampyx'' is an Ordovician-Silurian genus of Asaphida, Asaphid trilobites of the family (biology), family Raphiophoridae. Species of ''Ampyx'' are characterized by three extended spines on the head-shield, one spine derived from each free cheek, ...

'', ** '' Ampyxinella'' ; *:The

Agnostida Agnostida is an order of arthropod which have classically been seen as a group of highly modified trilobites, though some recent research has doubted this placement. Regardless, they appear to be close relatives as part of the Artiopoda. They a ...

order is present, with: ** '' Micragnostus calvus'', ** '' Anglagnostus dux'', ** '' Geragnostus mediterraneus'', ** '' Arthrorhachis''; *:

Ptychopariida Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. The earliest species occurred in the second half of the Lower Cambrian, and the last species did not survive the Ordovician–Silurian ...

order: ** '' Euloma filacovi'', ** '' Solenopleuropsis ribeiro''; *:

Phacopida Phacopida ("lens-face") is an order of trilobites that lived from the Late Cambrian to the Late Devonian. It is made up of a morphologically diverse assemblage of taxa in three related suborders. Characteristics Phacopida had 8 to 19 thorac ...

order : ** '' Platycalymene''. Other fossil remains of marine animals are known from the formation: *

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...

s ; * molluscs : **

bivalves 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 ...

, ** rostroconchs, **

monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell inhabiting deep sea environments . Extant representatives were not recognized as such until 1952; previously they were known only from ...

ns ; *

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

s ; * échinoderms ; *

graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and ...

References

{{reflist Geologic formations of France Ordovician System of Europe Ordovician France Ordovician south paleopolar deposits