The Tsaté Nappe

The Tsaté Nappe also called the shiny shale zone (schistes lustrés), is a mixture of rocks representing what is left of the Alpine Ocean, also call Piémontais Ocean, or Alpine Tethys. These serpentinites (stop sign E-8), metagabbros, metabasalts, or prasinites from the oceanic crust originate from the middle Jurassic to the lower Cretaceous sea-floor spreading. The associated sediments are represented by calcareous schists, some from the Upper Cretaceous, (Série Grise, grey flysch type series and the Série Rousse).  Pure white limestone representing the Upper Jurassic is also existent. Less frequently, red and green radiolarites can be found representing mid-ocean ridge, pelagic deposits.  

NB: The ocean remnants in the Tsaté Nappe mainly represent the northern part of the Alpine Ocean, north of the mid-ocean ridge. The remnants of the southern part were detached and transported to the Prealps forming the upper nappes, rich in flysch deposits.  Underwater sedimentary flows called turbidities, reworking sand and clay of Austroalpine origin create specific sequences, called flysch.

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At the base of the Tsaté Nappe two tectonic slivers are embedded in the Tsaté calcschists: the Frilihorn and the Cîmes Blanches.  Containing rocks from between the Triassic to the Cretaceous, these slivers represent remnants of tilted blocks from the northern margin of the Alpine Ocean. The breccias around Pic d’Artsinol and in Villa belong to the Cimes Blanches unit.