Tournaisian
The Tournaisian ( in German language, usually shortened to Tournai ) is in Earth's history, a period of the Carboniferous ( Paleozoic ). In the Chronostratigraphy it is the lowest level of Mississippiums or the only stage of the lower Mississippian series. The stage includes geochronological the period from about 358.9 million to about 346.7 million years. The step follows the Famennian stage of the Devonian and is separated from the Carboniferous Viseum level.
Naming and history
The stage is named after the city of Tournai ( Doornik ) in Belgium. The division of the Central European Lower Carboniferous (or Dinantium ) in two stages goes back to André Dumont (1832 ). Laurent -Guillaume de Koninck ( 1842-44 ) named these two parts with " calcaire Carbonifère de Tournai " and " calcaire Carbonifère de Visé ". It was a lithostratigraphic subdivision in the first place. 1860 led Gosselet the " étage du calcaire de Tournai ". In the legend of the six sheets of the Geological Map of Belgium ( Dupont, 1882-1883 ) was from the " étage de Tournai ".
Definition and GSSP
The base of the stage is defined by the first appearance of the conodont species Siphonodella sulcata within the line of development of Siphonodella praesulcata to Siphonodella sulcata. The limit was applied to the base of the bank 89 of the La Serre profile. The upper limit of the stage is marked by the first appearance of the fusulinids Type Eoparastaffella simplex ( Morphotype 1/Morphotype 2). The official reference profile of the International Commission on Stratigraphy ("Global Stratotype Section and Point" = GSSP ) for the Tournaisian is the La Serre profile in the southeastern Montagne Noire ( France). It is an approximately 80 cm deep blight on the southern slope of the mountain La Serre, about 125 meters south of the summit (252 m ), approximately 525 m east of the Maison La Roquette, 2.5 km northeast of the town Fontès (Dept. Hérault, cabrières, France).
According to recent studies, the conodont species Siphonodella sulcata already is but one at the base of the bank 85 of the La Serre profile. The original GSSP and the first appearance of the conodont species Siphonodella sulcata therefore no longer matches exactly.
Regional breakdown
The Tournaisium was originally a regional level, which was used almost exclusively in Central and Western Europe. In other regions, other subdivisions of the Carboniferous were used. 1990 Tournaisium was ratified by the International Commission on Stratigraphy of the International Union of Geological Sciences ( IUGS ) as a global level. In Central and Western Europe Tournaisium is sub-divided by region into different sub-stages. In Germany it is correlated with the Balvium and the lower part of Erdbachium; both sub-stages are little used today. In Belgium, it is divided into sub- stages Hastarium and Ivorium. In England it is correlated with the lower level Courceyium and the lower part of Chadium. In other regions, other regional stages and sub-stages are used to divide the Mississippiums in use.
Biostratigraphic subdivision
The Tournaisium is divided into eight conodont biozones:
- Gnathodus pseudosemiglaber / Scaliognathus anchoralis zone
- Gnathodus semiglaber / Polygnathus communis Zone
- Dollimae bouckaerti zone
- Gnathodus typicus / Siphonodella isosticha zone
- Siphonodella quadruplicata / upper Patrognathus andersoni zone
- Lower Patrognathus andersoni zone
- Patrognathus variabilis Zone
- Patrognathus crassus Zone
It correlates with the MFZ1 to MFZ8 the foraminiferal Intervalzonen of Mississippiums. In the zonation of corals rugosen it corresponds to the zones RC1 to RC3, and the lower part of RC4 zone.