The Couches des Marmontains are a sedimentary formation deposited during the middle

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

(

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

). It consists of

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s and black

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

s. The formation is 5 to 30 m thick. 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 The Valais Ocean is a subducted oceanic basin which was situated between the continent Europe and the microcontinent Iberia or so called Briançonnais microcontinent. Remnants of the Valais ocean are found in the western Alps and in tectonic win ...

. Outcrops can be found north of

Bourg-Saint-Maurice Bourg-Saint-Maurice (; Arpitan: ''Bôrg-Sant-Mori'' or simply ''Le Bôrg''), popularly known as Bourg, is a commune in the Savoie department in the Auvergne-Rhône-Alpes region in south-eastern France. Located on the Italian border south of Cha ...

. The Couches des Marmontains can be found in the following nappes: * External Valais :*

Moûtiers unit Moûtiers (; Arpitan: ''Motiérs''), historically also called Tarentaise, is a commune in the Savoie department in the Auvergne-Rhône-Alpes region in Southeastern France. Moûtiers is the main access point to the Les Trois Vallées ski region ...

:* 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 () and the

Val Ferret Val Ferret is the name shared by two valleys separated by the Col Ferret, a pass on the border between Italy and Switzerland. The valleys lie southeast of Mont Blanc Massif. The Swiss valley drains northeast towards Orsières and on into the R ...

Orsières Orsières is a Municipalities of Switzerland, municipality in the district of Entremont (district), Entremont in the Cantons of Switzerland, canton of Valais in Switzerland. History Orsières is first mentioned in 972 as ''Pons Ursarii''. In medie ...

, Canton

Valais Valais ( , ; ), more formally, the Canton of Valais or Wallis, is one of the cantons of Switzerland, 26 cantons forming the Switzerland, Swiss Confederation. It is composed of thirteen districts and its capital and largest city is Sion, Switzer ...

Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

. It was first described in 1955 by

Rudolf Trümpy Rudolf Trümpy (16 August 1921 – 30 January 2009) was a Swiss geologist, who was born in the small Swiss town of Glarus. He graduated from the ETH Zürich in the late 1940s with a thesis titled: “Der Lias der Glarner Alpen”. From 1947 to 1953 ...

. The Marmontains Formation can be correlated with the Valzeina Formation of Graubünden and black shales in the

Engadin The Engadin or Engadine (;This is the name in the two Romansh idioms that are spoken in the Engadin, Vallader and Puter, as well as in Sursilvan and Rumantsch Grischun. In Surmiran, the name is ''Nagiadegna'', and in Sutsilvan, it is ''Gidegna'' ...

References

{{Reflist Geologic formations of France Geologic formations of Switzerland Cretaceous System of Europe Albian Stage Cenomanian Stage Cretaceous France Cretaceous Switzerland Geology of the Alps