Saint-Chinian Formation

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Saint-Chinian Formation
Stratigraphic range: Tremadocian
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Type Geologic formation
UnderliesLa Maurerie Formation
OverliesLa Dentelle Formation
Thicknessaround 500 m
Lithology
Primary Shale
Other Sandstone, Limestone
Location
Coordinates 43°25′07″N2°56′43″E / 43.418624°N 2.945366°E / 43.418624; 2.945366
Region Occitanie
Country France
Type section
Named for Saint-Chinian
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Saint-Chinian Formation (France)

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

Contents

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 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. [2]

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. [3] [4]

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. [5]

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" [6] ..

Nautiloids

GenusSpeciesLocalityAgeNotesImages
Cyclostomiceras C. thoraliEuloma filacovi ZoneLate Tremadocian A cyclostomiceratid ellesmerocerid [7]
Saloceras S. chinianenseEuloma filacovi ZoneLate Tremadocian An eothinoceratid ellesmerocerid [7]
S. murvielenseEuloma filacovi ZoneLate Tremadocian An eothinoceratid ellesmerocerid [7]
S. pradenseTaihungshania miqueli acme SubzoneLate Tremadocian An eothinoceratid ellesmerocerid [7]
Rioceras R. escandeiEuloma filacovi Zone ; Asaphelina barroisi berardi and Taihungshania miqueli SubzoneLate Tremadocian A rioceratid ellesmerocerid [7]
Felinoceras F. constrictumEuloma filacovi ZoneLate Tremadocian A rioceratid ellesmerocerid [7]
Annbactroceras A. martyiEuloma filacovi ZoneLate Tremadocian A baltoceratid orthocerid [7]
A. felinenseEuloma filacovi ZoneLate Tremadocian A baltoceratid orthocerid [7]
Bactroceras B. mourguesiEuloma filacovi ZoneLate Tremadocian A baltoceratid orthocerid [7]
Cochlioceras C.? aff. roemeriEuloma filacovi Zone ; Asaphelina barroisi berardi and Taihungshania miqueli SubzoneLate Tremadocian A baltoceratid orthocerid [7]
Thoraloceras T. bactroceroidesEuloma filacovi Zone ; Asaphelina barroisi berardi and Taihungshania miqueli SubzoneLate Tremadocian A troedsonellid dissidocerid [7]
Lobendoceras L. undulatumEuloma filacovi Zone ; Asaphelina barroisi berardi and Taihungshania miqueli SubzoneLate Tremadocian A protocameroceratid endocerid [7]

Trilobites

GenusSpeciesLocalityAgeNotesImages
Paramegalaspis P. immarginata Prades-sur-Vernazobre Late Tremadocian-Early Arenig An asaphid [8]
Asaphellus A. frequens Prades-sur-Vernazobre Late Tremadocian-Early Arenig An asaphid [8]
A.? sp. Félines-Minervois Late Tremadocian-Early Arenig An asaphid [8]
Aocaspis A. macrophtalmaLa Rouvelane, près de Prades-sur-Vernazobre Late Tremadocian-Early Arenig An nileid [9]
Geragnostus G. occitanus Saint-Chinian Early Arenig A geragnostid [10]
G. callavei Saint-Chinian Early Arenig A geragnostid [10]
G. pusio Saint-Chinian Early Arenig A geragnostid [10]
Micragnostus M. languedocensis Saint-Chinian Early Arenig A micragnostid [10]
Trinodus T. chinianensis Saint-Chinian Early Arenig A trinodid [10]
T. corpulentus Saint-Chinian Early Arenig A trinodid [10]
T. abruptus Saint-Chinian Early Arenig A trinodid [10]
T. oviformis Saint-Chinian Early Arenig A trinodid [10]

Echinoderms

GenusSpeciesLocalityAgeNotesImages
Arauricystis A. primaevaA cornute stylophoran [15]
A. occitanaA cornute stylophoran [15]
Cothurnocystis C. fellinensisA cornute stylophoran [15]
C. courtessoleiA cornute stylophoran [15]
Phyllocystis P. blayaciA cornute stylophoran [15]
P. crassimarginataA cornute stylophoran [15]
Thoralicystis T. griffeiA cornute stylophoran [15]
Trigonocarpus T. singularisA cornute stylophoran [15]
Chauvelicystis C. spinosaA cornute stylophoran [15]
C. vizcainoiA cornute stylophoran [15]
Galliaecystis G. lignieresiA cornute stylophoran [15]
G. ubaghsiA cornute stylophoran [15]
Amygdalotheca A. griffeiA cornute stylophoran [15]
Anatifopsis A. trapeziiformisA mitrate stylophoran [15]
Balanocystites B. escandeiA mitrate stylophoran [15]
Peltocystis P. cornutaA mitrate stylophoran [15]
Vizcainocarpus V. dentigerA mitrate stylophoran [15]
Chinianocarpos C. thoraliA mitrate stylophoran [15]
Minervaecystis M. vidaliA solute homoistelean [15]
Balantiocystis B. thoraliAn eocrinoïd [15]
Aethocrinus A. mooreiA cladide crinoïd [15]
Macrocystella M. azaiziA dichoporite rhombifere. Two subspecies are present : M. a. paucicristatus and M. a. multicristata [15]
Hemicystites H. boehmiA edrioasteroïd [15]
 ? Pyrgocystis  ?P. sp.A edrioasteroïd [15]
Chinianaster C. levyiA goniactinid stelleroïd [15]
Villebrunaster V. thoraliA goniactinid stelleroïd [15]
Ampullaster A. ubaghsiA goniactinid stelleroïd [15]
Pradesura P. jacobiA stenurid stelleroïd [15]

Other fossil remains of marine animals are known from the formation: [16]

References

  1. 1 2 "L'Ordovicien du bassin de Saint-Chinian" (PDF). Excursion ASNAT. 21 September 2019.
  2. 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
  3. 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
  4. 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.
  5. 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
  6. Thoral, Marcel (1946). "Cycles géologiques et formations nodulifères de la Montagne Noire". Publications du musée des Confluences, Année 1946. 1: 1–63.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 Kröger, B.; Evans, D. H. (2011). "Review and palaeoecological analysis of the late Tremadocian – early Floian (Early Ordovician) cephalopod fauna of the Montagne Noire, France". Museum für Naturkunde. 14 (1): 5–34. doi: 10.1002/mmng.201000013 .
  8. 1 2 3 Vidal, M. (1996). "Quelques Asaphidae (Trilobita) de la Formation de Saint-Chinian, Ordovicien inférieur, Montagne Noire (France): Systématique et paléoenvironnements". Geobios. 29 (6): 725–744. Bibcode:1996Geobi..29..725V. doi:10.1016/S0016-6995(96)80018-0.
  9. Dolambi, T.; Gond, P. (1992). "Aocaspis nov. gen., nouveau Trilobite Nileidae de l'Ordovicien inférieur de Montagne Noire (France)". Geobios. 25 (2): 213–224. Bibcode:1992Geobi..25..213D. doi:10.1016/S0016-6995(06)80400-6.
  10. 1 2 3 4 5 6 7 8 Howell, B. F. (1935). "Cambrian and Ordovician trilobites from Herault, southern France". Journal of Paleontology. 9 (3): 222–238.
  11. 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.
  12. 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.{{cite book}}: CS1 maint: location missing publisher (link)
  13. 1 2 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.
  14. 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.
  15. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Vizcaïno, D.; Lefebvre, B. (1999). "Les échinodermes du Paléozoïqueinférieur de Montagne Noire: Biostratigraphie et paléodiversité". Geobios. 32 (2): 353–356. Bibcode:1999Geobi..32..353V. doi:10.1016/S0016-6995(99)80049-7.
  16. 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.