Mississippian (middle Tournaisian-late Serpukhovian) lithostratigraphic and tectonosedimentary units of the southeastern Montagne Noire (Hérault, France)

Abstract

The tectonosedimentary and lithostratigraphic units of the Mont Peyroux nappe and Cabrières klippes, in the southeastern Montagne Noire, are revised. The Mont Peyroux nappe displays two Mississippian groups: SaintNazaire-de-Ladarez and Barrac. The Saint-Nazaire-deLadarez Group includes the traditional formations of Lydiennes, Faugères and Colonnes. The Barrac Group (new group) encompasses the Puech Capel Fm (with two new members: Puech Capel Mb and Landeyran Barn Mb), and the new Barrac and Fabrègues formations. The Puech Capel Mb corresponds to a period of erosion, reworking, and debris flow deposition in the basin, linked to a major tectonic event; hence, the distinction between two groups is made here. The Barrac Fm, overturned and normal, with classical Bouma turbidites, and without carbonate olistoliths, ends west of the Fabrègues Formation, bearing a few latest Viséan to Serpukhovian olistoliths. The Cabrières klippes contain numerous Ordovician, Silurian, Devonian and Mississippian klippes and olistoliths included in a detrital unit (formerly Flysch-units III-IV or Laurens Flysch Group); they are re-named here as the Laurens-Cabrières Group, and subdivided into three new complexes: the Laurens Complex, Roquessels Complex and Vailhan-Cabrières Complex. The Laurens Complex is not yet subdivided into formations. The Roquessels Complex shows characteristically the new Coteau de Bergue Fm and the Lentilles de la route D13 informal unit (including the former grauwacke de Roquessels). The Vailhan-Cabrières Complex is composed of three klippes: Vissou, La Serre and Tourière-Escandolgue -Mougno (TEM), and various disseminated smaller olistoliths, which are Early Ordovician to late Serpukhovian (Protvian) in age. The Vissou klippe probably corresponds to a fragment of the overturned limb of the Mont Peyroux nappe, because it exposes the traditional inverse succession of the Saint-Nazaire-de-Ladarez Group, followed by the equivalent of the Puech Capel Mb, with carbonate slumps and sandy turbidites. In the La Serre klippe, a new La Serre East Fm is described as the unique formation of Montagne Noire with late Tournaisian-early Viséan shallow carbonates. In the Vailhan-Cabrières Complex, several formations are defined or redefined in the Mississippian klippes and olistoliths: Tourière Fm (former secondes griottes), Combe Rolland Fm (former bancs de dessus), Valuzières Fm (former calcaires du sommet 224- Valuzières), Oolites of Roc de Murviel Fm, Roque Redonde Fm, Roc de Murviel Fm, and La Serre de Péret Fm. The four latter formations correspond to the former Calcaires à Productus. The Laurens-Cabrières Group in Cabrières is relatively distinct, and exhibits possible prodeltaic units within the poudingue à dragées (candy conglomerates), sandstone with “Namurian A” terrestrial plants fragments, and Phillipsia sandstones, designated here as the MougnoLes Batailles informal unit. Some carbonate units associated with these prodeltaic deposits, such as the Spanish Scarf and other “bioherms of Cabrières”, seem to be affected by small displacements (Escandolgue, Japhet). Palaeogeographic and tectonic implications lead to the structural hypothesis of a Mont Peyroux-Cabrières unit, including together the Mont Peyroux nappe and the Cabrières klippes, which initially was thrust and deposited in the Axial Zone, and then glided southward to its current location.