«Murchisoni-Kalk»

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

• glauconite

• nummuliti

Nummulites "Murchisoni"

Gerarchia e successione

Unità sovrastante

• «Granulosa-Kalk»

Età

Geomorfologia

• tardo Ypresiano

Età alla base

• Ypresiano medio

Paleogeografia e tettonica

• Terziario

Paleogeografia

North Tethyan Shelf (Helv.) :
marge continentale européenne

Termini generici

• Östliches Helvetikum :
  u.a. Glarner Alpen

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).