The Marnes Brunes Inférieures in the Grand Coyer remnant: characteristics, structure and relationship to the Grès d’Annot

Abstract

Abstract Part of the Alpine foreland basin, the Grand Coyer remnant lies in a NW-SE-trending syncline and contains turbidity current deposits derived from the south. Palaeotopography of the Marnes Bleues surface is complex but there is generally a NE-dipping confining slope in the west of the area. Palaeocurrent data suggest that aside from localized alteration of flow paths, the mean direction of flow was parallel to this slope. Three sections (Vallon de Fouès & Carton, Laupon and Sommet de la Mole) are used to illustrate the nature of the Marnes Brunes Inférieures—a transitional facies between the Marnes Bleues and the Grès d’Annot. The Marnes Brunes Inférieures is typically thin-bedded, sharp-based and sharp-topped, non-graded, predominantly very fine-grained sands, with planar and ripple lamination, interbedded with thin marls and shale. The finer grained Marnes Brunes Inférieures in the Grand Coyer area is interpreted as a distal and lateral equivalent of the coarser Grès d’Annot, which is generally thought to represent deposition along the main axis of flow. Examples are provided of how these characteristics change away from the onlap slope. Evidence is presented to illustrate the connection between syndepositional structural alteration and the common slumping observed within the Marnes Brunes Inférieures.