«Murchisoni-Kalk»

Retour à «Mittlerer Grünsand»

Représentation et statut

Couleur CMYK
N/A
Couleur RGB
R: 120 G: 120 B: 120
Rang
unité lithostratigraphique
Usage
Ce terme n'est pas en usage.
Status
terme incorrect (mais utilisé de manière informelle)

Nomenclature

Deutsch
«Murchisoni-Kalk»
Français
«Calcaire à Nummulites murchisoni»
Italiano
«Calcare a Nummulites murchisoni»
English
«Murchisoni Limestone»
Origine du nom

Namengebendes Fossil: Foraminiferenart Nummulites murchisoni. Diese Art ist jedoch bis im unteren Teil des «Grauen Nummulitenkalks» vorhanden.

Variantes historiques

Murchisonikalk = Murchisonkalk [sic] (Jeannet et al. 1935), Granulosa-Murchisonikalk (Ochsner 1975), Murchisoni horizon (Lihou 1995), Nummulitenkalk

Description

Épaisseur
1,1 - 2 m ; 1,6m am Sihlsee (Jeannet et al. 1935)

Composants

Minéraux
  • glauconite
Fossiles
  • nummulites

Nummulites "Murchisoni"

Hiérarchie et succession

Unités sus-jacentes

Âge

Âge au sommet
  • Yprésien tardif
Âge à la base
  • Yprésien moyen

Paléogéographie et tectonique

  • Tertiaire
Paléogéographie
plateforme nord téthysienne :
marge continentale européenne
Termes génériques
Type de protolithe
  • sédimentaire
Conditions de formation

neritisch

Métamorphisme
non métamorphique

Références

Révision
Lihou Joanne C. (1995) : A new look at the Blattengrat unit of eastern Switzerland: Early Tertiary foreland basin sediments from the south Helvetic realm Eclogae geol. Helv. 88/1, 91-114

p.104: The first hardground in the Nummulitic Limestone marks the base of the Murchisoni horizon, named after the common occurrence of Nummulites murchisoni, a lower to middle Cuisian nummulite (Schaub 1981). In Weisstannental, the Murchisoni horizon is represented by a calcareous greensand with echinoderm debris, that passes southeastwards into a sandy limestone at Gula-Schwamm (Fig. 5). East of Elm, the same stratigraphic horizon thickens to the south and passes into a limestone-rich facies in the Fanenstock profile (Fig. 4). There, the hardground is overlain by a limestone breccia containing Operculina sp. and Globigerina sp.; whilst Operculina sp. inhabits a range of water depths (0-130 m) (Murray 1991), globigerinids are rare at depths of less than 40 m, and only abundant above 80-100 m (Brasier 1980). The limestone breccia passes upwards into a glauconitic foraminiferal limestone with very big nummulitids and discocyclinids; the bias towards large B-form nummulitids either arose by winnowing out of smaller A-forms by bottom currents, or selective transport of larger forms during high energy storm events (Crampton 1992). In situ faunas are dominated by A-forms in an A:B ratio of 10:1 (Blondeau 1972).
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