Calcaire à gryphées

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The Calcaire à gryphées ( Eng . Gryphäenkalk ) is a sedimentary formation in France . It was deposited in the Lower Jurassic ( Hettangian and Sinemurian ).

designation

The Calcaire à gryphées, derived from the French calcaire (lime), is a limestone formation with a large number of gryphées (French: gryphées ).

Occurrence

Gryphaea

The Calcaire à gryphées occurs mainly in the Paris Basin in the lower layer of the Lias . But it is also present in the Lower Jura of the Rhône trench near Lyon .

stratigraphy

The Calcaire à gryphées immediately follows the underlying Marnes de Levallois des Rhaetiums . For its part, it is concordantly overlaid by the Argiles à Promicroceras (or Marnes et argillites à ammonites ). In north-eastern Lorraine the sand body of the Grès d'Hettange pushes into the Calcaire à gryphées .

Lithology

The calcaire à gryphées, which can reach a maximum thickness of between 60 and 70 meters, consists mainly of an alternation of 10 to 40 centimeters thick, gray, marly limestone banks and dark blue marl layers . The marl layers weather yellowish, contain pyrite and are bituminous in places . The formation is built up from a total of 35 of these alternating sequences.

The inclusion of sand bodies in the Grès d'Hettange does not immediately merge into the normal sequence of the Calcaire à gryphées, but is replaced by a chalky-sandy sequence after the formation of an emersion surface.

geomorphology

The Calcaire à gryphées, together with the Grès d'Hettange, forms the clear stratification of the Côte du Lias .

Fossil content

In addition to frequently and location occurring Gryphäen with Gryphaea arcuata , there are other bivalves such as Chlamys , Entolium , Liostrea , Ostrea irregularis , Pinna , Plagiostoma gigantea , Pleuromya and Oxytoma , brachiopods (including Lingula , Rhynchonella as Rhynchonella defineri and Rhynchonella schimperi , Spiriferina with Spiriferina walcotti and Terebratulida ), Crinoidea with Chladocrinus tuberculatus , echinoderms , snails , corals , tubular calcareous worms and trace fossils of the Ichnotaxa Chondrites , Diplocraterion and Kulindrichnus . Occasionally, there are also scraps of wood . Belemnites such as Belemnites acutus and Nautilus occur in the uppermost section of the formation. The ammonites are not very common, but they are distributed throughout the formation. Among them Alsatites liasicus , Arietites bisulcatus , Arietites rariformis , Arnioceras semicostatum , Psiloceras johnstoni , Psiloceras planorbis and Schlotheimia angulata .

Deposit conditions

The absence of photophilic algae and zooxanthellae- bearing corals suggests a relatively low-light biocenosis of the benthic fauna (infra- to circumlittoral level). The existing endobionts such as gryphees, lingulids, pinnas, plagiostomas and others were adapted to a soft substrate. The undamaged preservation of these fossils suggests an only slightly agitated environment. However, there are also traces of erosion in some banks - an indication of a higher hydrodynamic regime, which is due to the influence of a deeper wave base (such as in storms).

The appearance of nectonic taxa (e.g. belemnites) in the uppermost section of the formation (lower Sinemurium) shows the increasing transgressive tendencies in the course of the hettangian, linked with a rise in sea ​​level . In a wider regional context, this process is part of the transgression of the Alpine Tethys Sea towards the Paris Basin, which began at the Triassic-Jura border , and which should reach its peak in the Pliensbachian and Toarcian .

Gryphae

Gryphae are very sensitive to environmental conditions. In murky, warm water and when there is a relative lack of oxygen near the ground, their growth is inhibited and they only form thin, wide shells. Under less turbid, cooler and better ventilated (less reducing) conditions, however, they develop large forms with thick shells due to an increased rate of calcification. For the Calcaire à gryphées there were mesotrophic, narrow and turbid conditions at the beginning of the formation in the hettangium. At that time, their sedimentation area was still isolated from the Tethys area by the high area around Lyon (French: éperon de Lyon ) and received a great deal of terrestrial erosion debris from the Ardennes in the north. Phototrophic conditions only established themselves in the hanging wall (from the Sinemurium).

Economical meaning

The calcaire à gryphées is an important raw material for the cement industry due to its marl content .

Age

The absolute age for the Calcaire à gryphées is not known. Biostratigraphically , however, the ammonite zones ( Psiloceras planorbis zone to Arnioceras semicostatum zone ) can be used to determine a sub-Hettangian to sub-Sinemurian age. The formation is believed to be 199 to 194 million years old BP .

swell

literature

  • Hilly, J. & Haguenauer, B .: Lorraine Champagne . In: Masson (ed.): Guides Géologiques Régionaux . 1979.

Individual evidence

  1. ↑ Hanzo, M. & Lathuiliere, B., Almeras, Y., Dagallier, G., Guerin-Franiatte, S., Guillocheau, F., Huault, V., Nori, L. & Rauscher, R .: Paléoenvironnements dans le Calcaire à gryphées du Lias de Lorraine, de la carrière de Xeuilley au Bassin Parisien . In: Eclogae geol. Helv. Band 93 , 2000, pp. 183-206 .
  2. ↑ Pautrot, C. et Hanzo, M .: Le mer au épicontinentale Lias . Ed .: Lexa-Chomard, A. & Pautrot, C. "Géologie et geographie de la Lorraine". Serpenoise, 2006, p. 100-109 .
  3. ↑ Thompson, JB, Mullins, HT, Newton, CR & Vercoutere, TL: Alternative biofacies model for dysaerobic communities . In: Lethaia . tape 18 , 1985, pp. 167-179 .
  4. ↑ Debrand-Passard, S. inter alia: Synthèse géologique du Sud-Est de la France . In: Mém. Bur. Rech. Géol. Min. 1984.

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