Variation in structural styles within fold-and-thrust belts: Insights from field mapping, cross-sections balancing, and 2D-kinematic modelling in the Jura mountains (Eastern France)

Abstract

Fold-and-thrust belts developed above an evaporite décollement host structural traps where geofluids, including hydrocarbons, can accumulate. A valid and accurate structural style intepretation is therefore crucial to understand the three-dimensional geometries in the subsurface, in order to better model geofluid reservoirs and to increase success during exploration. Here, we present a multidisciplinary approach to unravel the subsurface structural styles of the Jura fold-and-thrust belt (eastern France), combining geological mapping, from regional to outcrop scale, with cross-section balancing and 2D-kinematic forward modelling. Results show that the Jura fold-and-thrust belt is characterized by mixed structural styles. Evaporite-cored folds are similar to those commonly observed in fold-and-thrust belt characterized by a thick salt-bearing basal detachment (e.g. Zagros fold-and-thrust belt), while fault-bend fold geometries and the emplacement of thrust sheets are similar to those occurring in fold-and-thrust belts characterized by multiple and thin detachment horizons within the sedimentary sequence (i.e. Canadian Rocky Mountains). In the Jura, the flow of evaporites in most cases is inhibited, as anhydrites and salt form thin layers and are mixed with mechanically stronger rocks, such as marls and dolostones. Results from this study can be used as a benchmark to compare structural styles within other fold-and-thrust belts characterized by lithological variation within the evaporite-bearing basal detachment at the regional scale and by multiple detachment layers within the sedimentary sequence.