«Murchisoni-Kalk»

Torna a Mélange del Mättental

Rappresentazione e statuto

Colore CMYK
N/A
Colore RGB
R: 120 G: 120 B: 120
Rango
unità litostratigrafia
Uso
Unità non usata
Status
termine scorretto (informale)

Nomenclatura

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

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

Varianti storiche

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

Descrizione

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

Componenti

Minerali
  • glauconite
Fossili
  • nummuliti

Nummulites "Murchisoni"

Gerarchia e successione

Unità sovrastante

Età

Geomorfologia
  • tardo Ypresiano
Età alla base
  • Ypresiano medio

Paleogeografia e tettonica

  • Terziario
Paleogeografia
North Tethyan Shelf (Helv.) :
marge continentale européenne
Termini generici
Tipo di origine
  • sedimentaria
Condizioni di formazione

neritisch

Metamorfismo
non metamorfo

Referenze

Revisione
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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