Marmontains Formation

Couches des Marmontains Stratigraphic range: Albian PreЄ Є O S D C P T J K Pg N
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

1. Loprieno, Andrea. "http://earth.unibas.ch/tecto/research/Diss_Loprieno_2001_small.pdf" (PDF). Retrieved 21 February 2013. External link in |title= (help)
2. Loprieno, Andrea (2011). "The Valais units in Savoy (France): a key area for understanding the palaeogeography and the tectonic evolution of the Western Alps".
3. "Couches des Marmontains". Lithostratigraphisches Lexikon der Schweiz. Retrieved 25 February 2013.
4. 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.