Publication Date:
2007-10-08
Description:
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 Foues & Carton, Laupon and Sommet de la Mole) are used to illustrate the nature of the Marnes Brunes Inferieures--a transitional facies between the Marnes Bleues and the Gres d'Annot. The Marnes Brunes Inferieures 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 Inferieures in the Grand Coyer area is interpreted as a distal and lateral equivalent of the coarser Gres 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 Inferieures.
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