The front of the Helminthoid Flysch Nappe upon the Barcelonnette window (Western Alps) ; new observations and tectonic implications
Year: 2026
Type: article
Abstract: We report on the area of the Jausiers-Col de la Bonette road, which is the highest of Europe, based on personal observations and the literature, including the published geological maps (BRGM Infoterre application). The tectonic pile comprises, 1) the folded Barcelonnette Autochthon (Keuper evaporites to marly Upper Jurassic-Lower Cretaceous); 2) various Subbriançonnais units (Séolanes platform facies), 3) some slivers from the classical Briançonnais (e.g., Ventebrun sliver); 4) the Roche Chevalière sliver described since years as originating from the Acceglio domain of eastern Briançonnais ; 5) the unconformable Neoauochthon Priabonian-Rupelian of the Grès d’Annot Basin ; 6) various sub-units of the Parpaillon Flysch, i.e., the Cretaceous-Paleocene turbidites that form the bulk of the Embrunais-Ubaye (Emb-Ub) Nappe (Flysch and basal Subbriançonnais-Briançonnais slivers). The Chevalier sub-unit of the Parpaillon Flysch (ParC) extends on top of and below the Roche Chevalière sliver, whereas the main Parpaillon sub-units extend further ENE. The sheared, brecciated « Schistes à blocs » and « Restefond Tectonic mélange » (uncorrectly described as « Autapie nappe » in previous works) underlie the Parpaillon units when they extend on top of the Neoautochthon formations. The Roche Chevalière sliver is non-metamorphic contrary to the blueschist facies Acceglio-type units of eastern Briançonnais. Sampling of Roche Chevalière by the WNW-going Flysch prism occurred before the eastward subduction of the Briançonnais margin at c. 37 Ma. The Roche Chevalière sliver remained at low temperature close to 260 °C when it crossed the exhumed Briançonnais units (cf. Furfande klippes) ; it reached its frontal position at c. 30 Ma, when the Rupelian sediments were still rich in interstitial water. The complex setting of the area is linked to the post-Rupelian folding and faulting that affected the Flysch and underlying units.
DOI: 10.1051/bsgf/2026011
Language: English
Subfield: Geophysics
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $539
OpenAlex ID: W7204468244