Saint-Chinian Formation

Saint-Chinian Formation
Saint-Chinian Formation
Stratigraphic range:
	Geragnostus mediterraneus
Type	Geologic formation
Underlies	La Maurerie Formation
Overlies	La Dentelle Formation
Thickness	around 500 m
Lithology
Primary	Shale
Other	Sandstone
Location
Coordinates	43.418624°N 2.945366°E
Region	Occitanie
Country	France
Type section
Named for	Saint-Chinian
	Saint-Chinian Formation (France)

The Saint-Chinian Formation is a geological formation composed of shales with limestone inclusions, dating from the Lower Ordovician (Tremadocian).

It is one of the six geological formations from the Saint-Chinian Cambro-Ordovician 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 in Southern France.[1]

The formation received its name from the small city of Saint-Chinian, a commune located in the Hérault department in Occitania.

It is dated from the biostratigraphic sub-zone characterized by Taihungshania miqueli and Asaphelina barroisi berardi.[1]

Paleoenvironment

The thin nature of the silico-clastics deposits, the presence of slump, combined with a trilobite fauna dominated by members of the Asaphidae family indicates a marine environment of external distal platform.[2]

Paleofauna

Shales of the Saint-Chinian Formation bears in certain areas accumulations of phosphated nodules, each potentially bearing a trilobite. Those are the so-called "schistes à gateaux"[3]..

Trilobites:[4]
Members from the Asaphida order and the Asaphidae family are commons :
- Asaphelina barroisi barroisi,
- Asaphelina barroisi berardi,
- Niobella ligneresi,
- Paramegalaspis immarginata,
- Asaphellus frequens,
- Taihungshania miqueli,
- Ampyx priscus,[5]
- Ampyxinella ;
The Agnostida order is present, with:[6]
- Micragnostus calvus,
- Anglagnostus dux,
- Geragnostus mediterraneus,
- Arthrorhachis;[7]
Ptychopariida order:
- Euloma filacovi,
- Solenopleuropsis ribeiro;[8]
Phacopida order :
- Platycalymene.[7]

Other fossil remains of marine animals are known from the formation:[9]

brachiopods ;
molluscs :
- bivalves,
- rostroconchs,
- monoplacophorans ;
gastropods ;
échinoderms ;
graptolites.

References

"L'Ordovicien du bassin de Saint-Chinian" (PDF). Excursion ASNAT. 21 September 2019.
Vidal, Muriel (1996). "Some Asaphidae from the Saint-Chinian Formation, Lower Ordovician, Montagne Noire (France): Systematics and palaeoenvironments". Geobios. 29 (6): 725–744. doi:10.1016/S0016-6995(96)80018-0.
Thoral, Marcel (1946). "Cycles géologiques et formations nodulifères de la Montagne Noire". Publications du musée des Confluences, Année 1946. 1: 1–63.
Capera, J. C.; Courtessole, R.; Pillet, J. (1978). "Contribution à l'étude de l'Ordovicien inférieur de la Montagne Noire : biostratigraphie et révision des Agnostida". Annales de la Société Géologique du Nord. 98 (1): 67–87.
Thoral, M. (1935). Imprimerie de la Charité (ed.). Contribution à l'étude paléontologique de l'Ordovicien inférieur de la Montagne Noire et révision sommaire de la faune cambrienne de la Montagne Noire. Montpellier. pp. 362 pp.
Howell, B. F. (1935). "Cambrian and Ordovician trilobites from Herault, southern France". Journal of Paleontology. 9 (3): 222–238.
Vizcaino, D.; Alvaro, J.; Lefebvre, B. (2001). "The lower Ordovician of the southern Montagne Noire". Annales de la Société Géologique du Nord. 8 (2): 213–220.
Alvaro, J.; Lefebvre, B.; Vizcaino, D. (2001). "Catalogue of the fossil species defined in the Lower Paleozoic of the southern Montagne Noire". Annales de la Société Géologique du Nord. 8 (2): 227–232.
Babin, C.; Courtessole, R.; Melou, M.; Pillet, J.; Vizcaino, D.; Yochelson, E. L. (1982). Brachiopodes (Articulés) et mollusques (bivalves, rostroconches, monoplacophores, gastéropodes) de l'Ordovicien inférieur (Trémadocien-Arenigien) de la Montagne Noire (France méridionale). pp. 1–63.

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[ASNAT_2019-1] "L'Ordovicien du bassin de Saint-Chinian" (PDF). Excursion ASNAT. 21 September 2019.

[Vidal_1996-2] Vidal, Muriel (1996). "Some Asaphidae from the Saint-Chinian Formation, Lower Ordovician, Montagne Noire (France): Systematics and palaeoenvironments". Geobios. 29 (6): 725–744. doi:10.1016/S0016-6995(96)80018-0.

[3] Thoral, Marcel (1946). "Cycles géologiques et formations nodulifères de la Montagne Noire". Publications du musée des Confluences, Année 1946. 1: 1–63.

[4] Capera, J. C.; Courtessole, R.; Pillet, J. (1978). "Contribution à l'étude de l'Ordovicien inférieur de la Montagne Noire : biostratigraphie et révision des Agnostida". Annales de la Société Géologique du Nord. 98 (1): 67–87.

[Thoral_1935-5] Thoral, M. (1935). Imprimerie de la Charité (ed.). Contribution à l'étude paléontologique de l'Ordovicien inférieur de la Montagne Noire et révision sommaire de la faune cambrienne de la Montagne Noire. Montpellier. pp. 362 pp.

[6] Howell, B. F. (1935). "Cambrian and Ordovician trilobites from Herault, southern France". Journal of Paleontology. 9 (3): 222–238.

[Vizcaino_2001-7] Vizcaino, D.; Alvaro, J.; Lefebvre, B. (2001). "The lower Ordovician of the southern Montagne Noire". Annales de la Société Géologique du Nord. 8 (2): 213–220.

[8] Alvaro, J.; Lefebvre, B.; Vizcaino, D. (2001). "Catalogue of the fossil species defined in the Lower Paleozoic of the southern Montagne Noire". Annales de la Société Géologique du Nord. 8 (2): 227–232.

[9] Babin, C.; Courtessole, R.; Melou, M.; Pillet, J.; Vizcaino, D.; Yochelson, E. L. (1982). Brachiopodes (Articulés) et mollusques (bivalves, rostroconches, monoplacophores, gastéropodes) de l'Ordovicien inférieur (Trémadocien-Arenigien) de la Montagne Noire (France méridionale). pp. 1–63.