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.

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.

Paleoenvironment The Saint-Chinian Formation was deposited in a deep-marine setting along the southern margin of the Montagne Noire during the Tremadocian (Early Ordovician). The succession is dominated by dark grey to black shales interbedded with fine-grained sandstones and thin limestone layers, interpreted as distal turbidites. These lithologies reflect sedimentation on an outer shelf to slope environment, characterized by low energy conditions and episodic gravity flows.Álvaro, J. J., Vizcaïno, D., & Vennin, E. (2001). The Lower Ordovician of the southern Montagne Noire (France): sedimentology and sequence stratigraphy of a deep-shelf to slope basin. Geological Magazine, 138(5), 529–548. https://doi.org/10.1017/S0016756801005635

The thin nature of the silico-clastics deposits, the presence of slump structures, graded bedding, and synsedimentary deformation combined with a trilobite fauna dominated by members of the Asaphidae family, indicates periodic slope instability, possibly linked to tectonic activity. The fauna, including trilobites and cephalopods, suggests oxygenated bottom waters and an open marine setting.Vidal, M. (1996). La biodiversité de la faune de trilobites de la Formation de Saint-Chinian (Tremadocien supérieur, Montagne Noire, France). Geobios, 29(6), 743–751. https://doi.org/10.1016/S0016-6995(96)80041-2

Biogeographically, the assemblages show affinities with other Tremadocian faunas from northern Gondwana, including those of Morocco, Bohemia, and the Iberian Peninsula. The formation provides important data for regional paleogeographic reconstructions and for understanding early Ordovician biodiversification in peri-Gondwanan basins.Kröger, B., & Evans, D. H. (2011). Early Ordovician cephalopods from the Montagne Noire (France): taxonomy and biostratigraphic significance. Fossil Record, 14(1), 5–54. https://doi.org/10.1002/mmng.201000013

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".

Nautiloids

Genus Species Locality Age Notes Images Cyclostomiceras C. thoraliEuloma filacovi Zone Late Tremadocian A cyclostomiceratid ellesmerocerid Saloceras S. chinianenseEuloma filacovi Zone Late Tremadocian An eothinoceratid ellesmerocerid S. murvielenseEuloma filacovi Zone Late Tremadocian An eothinoceratid ellesmerocerid S. pradenseTaihungshania miqueli acme Subzone Late Tremadocian An eothinoceratid ellesmerocerid Rioceras R. escandeiEuloma filacovi Zone; Asaphelina barroisi berardi and Taihungshania miqueli Subzone Late Tremadocian A rioceratid ellesmerocerid Felinoceras F. constrictumEuloma filacovi Zone Late Tremadocian A rioceratid ellesmerocerid Annbactroceras A. martyiEuloma filacovi Zone Late Tremadocian A baltoceratid orthocerid A. felinenseEuloma filacovi Zone Late Tremadocian A baltoceratid orthocerid<ref

name="Kröger2011"/>|| Bactroceras B. mourguesiEuloma filacovi Zone Late Tremadocian A baltoceratid orthocerid Cochlioceras C.? aff. roemeriEuloma filacovi Zone; Asaphelina barroisi berardi and Taihungshania miqueli Subzone Late Tremadocian A baltoceratid orthocerid Thoraloceras T. bactroceroidesEuloma filacovi Zone; Asaphelina barroisi berardi and Taihungshania miqueli Subzone Late Tremadocian A troedsonellid dissidocerid Lobendoceras L. undulatumEuloma filacovi Zone; Asaphelina barroisi berardi and Taihungshania miqueli Subzone Late Tremadocian A protocameroceratid endocerid

Trilobites

Genus Species Locality Age Notes Images Paramegalaspis P. immarginata Prades-sur-Vernazobre Late Tremadocian-Early Arenig An asaphid Asaphellus A. frequens Prades-sur-Vernazobre Late Tremadocian-Early Arenig An asaphid A.? sp. Félines-Minervois Late Tremadocian-Early Arenig An asaphid Aocaspis A. macrophtalma La Rouvelane, près de Prades-sur-Vernazobre Late Tremadocian-Early Arenig An nileid Geragnostus G. occitanus Saint-Chinian Early Arenig A geragnostid G. callavei Saint-Chinian Early Arenig A geragnostid G. pusio Saint-Chinian Early Arenig A geragnostid Micragnostus M. languedocensis Saint-Chinian Early Arenig A micragnostid Trinodus T. chinianensis Saint-Chinian Early Arenig A trinodid T. corpulentus Saint-Chinian Early Arenig A trinodid T. abruptus Saint-Chinian Early Arenig A trinodid T. oviformis Saint-Chinian Early Arenig A trinodid

Trilobites: Members from the Asaphida order and the Asaphidae family are commons : Asaphelina barroisi barroisi, Asaphelina barroisi berardi, Niobella ligneresi, Taihungshania miqueli, Ampyx priscus, Ampyxinella; The Agnostida order is present, with: Arthrorhachis; Ptychopariida order: Euloma filacovi, Solenopleuropsis ribeiro; Phacopida order : Platycalymene.

Echinoderms

Genus Species Locality Age Notes Images Arauricystis A. primaeva A cornute stylophoran A. occitana A cornute stylophoran Cothurnocystis C. fellinensis A cornute stylophoran C. courtessolei A cornute stylophoran Phyllocystis P. blayaci A cornute stylophoran P. crassimarginata A cornute stylophoran Thoralicystis T. griffei A cornute stylophoran Trigonocarpus T. singularis A cornute stylophoran Chauvelicystis C. spinosa A cornute stylophoran C. vizcainoi A cornute stylophoran Galliaecystis G. lignieresi A cornute stylophoran G. ubaghsi A cornute stylophoran Amygdalotheca A. griffei A cornute stylophoran Anatifopsis A. trapeziiformis A mitrate stylophoran Balanocystites B. escandei A mitrate stylophoran Peltocystis P. cornuta A mitrate stylophoran Vizcainocarpus V. dentiger A mitrate stylophoran Chinianocarpos C. thorali A mitrate stylophoran Minervaecystis M. vidali A solute homoistelean Balantiocystis B. thorali An eocrinoïd Aethocrinus A. moorei A cladide crinoïd Macrocystella M. azaizi A dichoporite rhombifere. Two subspecies are present : M. a. paucicristatus and M. a. multicristata Hemicystites H. boehmi A edrioasteroïd ?Pyrgocystis ?P. sp. A edrioasteroïd Chinianaster C. levyi A goniactinid stelleroïd Villebrunaster V. thorali A goniactinid stelleroïd Ampullaster A. ubaghsi A goniactinid stelleroïd Pradesura P. jacobi A stenurid stelleroïd

Other fossil remains of marine animals are known from the formation: brachiopods; molluscs : bivalves, rostroconchs, monoplacophorans; gastropods; graptolites.

References