Saint-Chinian Formation
The Saint-Chinian Formation is a geological formation composed of shales with limestone inclusions, dating from the Lower Ordovician.
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. 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.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.
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.
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. thorali | Euloma filacovi Zone | Late Tremadocian | A cyclostomiceratid ellesmerocerid | |
| Saloceras | S. chinianense | Euloma filacovi Zone | Late Tremadocian | An eothinoceratid ellesmerocerid | |
| Saloceras | S. murvielense | Euloma filacovi Zone | Late Tremadocian | An eothinoceratid ellesmerocerid | |
| Saloceras | S. pradense | Taihungshania miqueli acme Subzone | Late Tremadocian | An eothinoceratid ellesmerocerid | |
| Rioceras | R. escandei | Euloma filacovi Zone ; Asaphelina barroisi berardi and Taihungshania miqueli Subzone | Late Tremadocian | A rioceratid ellesmerocerid | |
| Felinoceras | F. constrictum | Euloma filacovi Zone | Late Tremadocian | A rioceratid ellesmerocerid | |
| Annbactroceras | A. martyi | Euloma filacovi Zone | Late Tremadocian | A baltoceratid orthocerid | |
| Annbactroceras | A. felinense | Euloma filacovi Zone | Late Tremadocian | A baltoceratid orthocerid | |
| Bactroceras | B. mourguesi | Euloma filacovi Zone | Late Tremadocian | A baltoceratid orthocerid | |
| Cochlioceras | C.? aff. roemeri | Euloma filacovi Zone ; Asaphelina barroisi berardi and Taihungshania miqueli Subzone | Late Tremadocian | A baltoceratid orthocerid | |
| Thoraloceras | T. bactroceroides | Euloma filacovi Zone ; Asaphelina barroisi berardi and Taihungshania miqueli Subzone | Late Tremadocian | A troedsonellid dissidocerid | |
| Lobendoceras | L. undulatum | Euloma 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 | |
| Asaphellus | 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 | |
| Geragnostus | G. callavei | Saint-Chinian | Early Arenig | A geragnostid | |
| Geragnostus | 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 | |
| Trinodus | T. corpulentus | Saint-Chinian | Early Arenig | A trinodid | |
| Trinodus | T. abruptus | Saint-Chinian | Early Arenig | A trinodid | |
| Trinodus | 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
Other fossil remains of marine animals are known from the formation:
- brachiopods ;
- molluscs :
- * bivalves,
- * rostroconchs,
- * monoplacophorans ;
- gastropods ;
- graptolites.