Marmontains Formation
| Couches des Marmontains Stratigraphic range: Albian | |
|---|---|
| Type | Geological formation |
| Unit of | Valais trilogy |
| Underlies | Couches de Saint Christophe |
| Overlies | Couches de l’Aroley |
| Thickness | 5 to 30 m |
| Location | |
| Coordinates | 45°41′46″N 6°44′04″E / 45.696144°N 6.734438°ECoordinates: 45°41′46″N 6°44′04″E / 45.696144°N 6.734438°E |
| Region | Savoie |
| Country | France |
| Type section | |
| Named for | L’arête des Marmontains |
The Couches des Marmontains are a sedimentary formation deposited during the middle Cretaceous (Albian to Cenomanian). It consists of sandstones and black shales. The formation is 5 to 30 m thick.[1] The Couches des Marmontains overly the Couches de l’Aroley and underlie the Couches de Saint Christophe. All three units together make up the post-rift sequence of the Valais ocean. Outcrops can be found north of Bourg-Saint-Maurice.[2]
The Couches des Marmontains can be found in the following nappes:
- External Valais
- Moûtiers unit
- Roc de l'Enfer unit
- Petit St. Bernard unit
- Internal Valais
- Versoyen unit
The type locality and namesake of the formation is the mountain Marmontains (45°52′57″N 7°06′30″E / 45.88263°N 7.108412°E) and the Val Ferret in Orsières, Canton Valais, Switzerland. It was first described in 1955 by Rudolf Trümpy.[3]
The Marmontains Formation can be correlated with the Valzeina Formation of Graubünden and black shales in the Engadine.[4]
References
- ↑ Loprieno, Andrea. "http://earth.unibas.ch/tecto/research/Diss_Loprieno_2001_small.pdf" (PDF). Retrieved 21 February 2013. External link in
|title=(help) - ↑ Loprieno, Andrea (2011). "The Valais units in Savoy (France): a key area for understanding the palaeogeography and the tectonic evolution of the Western Alps".
- ↑ "Couches des Marmontains". Lithostratigraphisches Lexikon der Schweiz. Retrieved 25 February 2013.
- ↑ Tricart, Pierre-Charles de Graciansky, David G. Roberts, Pierre (2010). The Western Alps, from rift to passive margin to orogenic belt : an integrated geoscience overview (1st ed.). Amsterdam: Elsevier. p. 153. ISBN 978-0444537249.