Couches des Marmontains
Stratigraphic range: Albian-Cenomanian ~
Type	Geological formation
Unit of	Valais trilogy
Underlies	Couches de Saint Christophe
Overlies	Couches de l’Aroley
Thickness	5 to 30 m (16 to 98 ft)
Location
Coordinates	45°41′46″N 6°44′04″E / 45.696144°N 6.734438°E / 45.696144; 6.734438
Region	Savoie
Country	France   Switzerland
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 / 45.88263; 7.108412) 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