A mid-Tournaisian-late Viséan carbonate ramp reconstructed from nappes and olistolites in the southern Montagne Noire (France)

Abstract

The mainly calcareous succession from the mid Tournaisian to the lower part of the upper Viséan in the Southern Montagne Noire Mont Peyroux nappes and Cabrières slices is sedimentologically revised. From the late Viséan, the Variscan orogeny affected the area, and the studied Mississippian part of the succession was considered as part (together with the Devonian) of a period of tectonic quiescence, later included as nappes and olistolites in a wildflysch. This study presents the facies from pelagic limestones, calciturbidites, bioclastic limestones and microbial limestones, and the relationship between platform and calciturbidites in the pre-orogenic context of the Montagne Noire basin during the Mississippian. The differences in the lithostratigraphy is analyzed by means of four tectonostratigraphical units (Mont Peyroux nappe, Roquessels band, Cabrières area and La Serre band) previously defined by other authors, that together with the deep-water Vieussan-Caragnas unit (not studied here due to the poverty in chronostratigraphical data) allow reconstructing the original carbonate platform. The latter seems to correspond to a ramp for the latest Tournaisian to early Viséan, and a distally-steppened ramp from the middle Viséan to the early late Viséan, including basin plain to slope as the deepest water environments, and middle ramp as the shallowest, except for the uppermost part of the succession, where the inner ramp is recognized. During this period, the shallowing tendency in the tectonostratigraphic units is well marked: Mont Peyroux nappe – Roquessels band – Cabrières area – La Serre band (from deeper to shallower), which differs from the shallowing trend defined by previous authors during the Devonian. Strong similarities are observed with the preserved Mississippian carbonates in the Mouthoumet Massif to the south, which might represent the shallowest water deposits of the ramp, not preversed in the Cabrières-La Serre areas.