An area covering the higher parts of the Turtmanntal, Mattertal and Val d'Anniviers has been mapped in detail. These valleys show natural cross sections through four superposed nappes belonging to the Middle Penninic Zone (Siviez-Mischabel nappe, Mont Fort nappe), to the Upper Penninic Zone (Tsaté nappe) and to the Lower Austroalpine Dent Blanche nappe.
The normal limb of the Siviez-Mischabel nappe was studied with particular attention:
The pre-Triassic basement includes an older unit, whose polymetamorphic history suggests a pre-Namurian age and shows similarities with "eo-hercynian" Devonian (?) events which affected the Variscan basement of central Europe. Upper Carboniferous and Permo-Triassic strata lie unconformably on these polycyclic units.
A lesser part of the Mesozoic and Paleogene cover (Barrhorn and Toûno units) still adhere to the basement, while the main part of the cover lies in more external position within the Préalpes médianes décollement nappe. The Barrhorn series (Middle Triassic to Middle Eocene) exhibits a classical internai Briançonnais sequence. The Jurassic transgressive strata overlie the tilted and eroded Triassic formations. A listric Mesozoic paleofault separates this unit from the even more reduced and condensed Toûno unit. The great similarities existing between the Barrhorn unit and the Spillgerten slice in the Préalpes médianes rigides suggests that they occupied adjacent positions in the Mesozoic Paleogeography of the Briançonnais realm. In the western part of the Siviez-Mischabel nappe, the sole visible eo-Triassic remuant represents the root-zone of this Médianes rigides unit. The occurence of evaporitic beds within the Lower Triassic (future prealpine units) or their lack (Barrhorn and Toûno units) are responsible for the dissimilar tectonic evolutions of both cover segments.
In this part of the Penninic Zone, the Tertiary structuration began at Upper Eocene time when the flysch nappes forming the so called "nappes supérieures des Préalpes" overthrusted the Briançonnais flysch. The future Siviez-Mischabel nappe and its remnant cover, the Barrhorn and Toûno units, underwent an early deformation during the décollement of the Préalpes médianes rigides units, prior to being overthrusted by the Upper Penninic an Austroalpine nappes. During this main thrusting event, basement and cover underwent a syn-metamorphic penetrative deformation in the upper greenschist facies. Late deformation phases involved the entire pile of nappes and concentrated in ductile shear zones.