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The North Helvetic Flysch between Pte. Des Martinets and Croix de Javerne, Canton Waadt, Western Switzerland1


The research area comprises three of the main tectonic units of the Swiss Alps on the eastern flank of the Rhône-valley between Martigny and Monthey; 1. The Aiguilles-Rouges-Gneisses and their autochthonous sedimentary cover as part of the Autochthone Massives in the adjacent. 2. The overturned limb of the recumbently isoclinally folded Morcles Nappe as part of the Helvetic Nappes in the hanging wall.
3. Intercalated between these two units North Helvetic Flysch crops out.

The rocks of the Aiguilles-Rouges-Massiv (Triassic to Cretaceous) and the Morcles Nappe (Cretaceous and Tertiary) were mapped and described according to their lithological characteristics. (map and legend)
The Tertiary North Helvetic Flysch was investigated using sedimentological, tectonical and petrographical techniques. It could be divided in two parts on sedimentological grounds:
In the lower area, the Flysch is composed of medium-bedded to thick-bedded turbidites, which mainly consist of medium-grained to very coarse-grained sands. These turbidites are interpreted as lower-fan deposits according to Walker (1978). Because of their petrographical and sedimentological characteristics, they are probably part of the Grès du Val d' Illiez Member.
The upper part of the Flysch consists of alternating laminated to at most middle-bedded marls and fine-grained sandstones. These sediments are interpreted as turbidites deposited at the boundary of the lower fan / basin plain according to Walker (1978) or as lobe-fringe facies according to Mutti (1977). In a few areas, this part of the Flysch is interpreted as contourites because of its characteristic sedimentology.
The upper part of the Flysch lies conformably on the Morcles limestones and is therefore assigned to the Morcles Nappe ("Morcles-Flysch"). Consequently, the contourites also originated in the same depositional environment as the rocks of the Morcles Nappe ("Morcles-Basin"). The original position of the depocenter has been found not very far to the South between the Aiguilles-Rouges-Massiv and the Mont-Blanc-Massiv.

Two models for the emplacement of the Flysch over the Aiguilles-Rouges-Massiv are proposed:
1. The Grès du Val d'Illiez is interpreted as autochthonous Flysch, which has been deposited in a northwestern direction at an early stage of the Molasse Basin. The middle part of the Flysch represents the thrustzone of the Morcles Nappe. The upper part of the Flysch ("Morcles-Flysch") was placed on top of the Grès du Val d'Illiez during the overthrusting.
2. The Morcles-Flysch is firstly deposited in the Morcles-Basin followed by the deposition of the Grès du Val d'Illiez. Later, both are overthrust on top of the Aiguilles-Rouges-Massiv together. In this case, the whole Flysch sequence corresponds to the Grès du Val d'Illiez Formation (lying inverse); the autochthonous Flysch of the Aiguilles-Rouges-Massiv is missing.
In both models, the cause and the direction of the bottom currents, which formed the contourites in the relatively restricted Morcles-Basin stay unclarified.


MUTTI, E., 1977. Distinctive thin-bedded turbidite facies and related depositional environments in the Eocene Hecho Group (South-central Pyrenees, Spain). Sedimentology, 24: 107-131.

WALKER, R.G., 1978. Deep-water sandstone facies and ancient submarine fans: Models for exploration for stratigraphic traps. AAPG Bull., 62/6: 932-966.

1PREUSCHE, Ch., 1994. Der Nordhelvetische Flysch zwischen Pte. des Martinets und Croix de Javerne, Kanton Waadt, Westschweiz. Unveröff. Dipl.-Arb., Geol. Inst. Univ. Freiburg, 94 S.

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