Timing and Distribution of Bedding-Parallel Veins, in Evaporitic Rocks, Bouhedma Formation, Northern Chotts, Tunisia

Bedding-parallel veins, 'BPV', are widespread worldwide especially within sediments of low permeability such as mudstones, marls and evaporitic formations. Gypsum, calcite or quartz fibrous minerals compose these geological features as well as less common components such as bitumen. These structures are heavily studied as they provide significant information about the paleo-stress states, host rock deformation and fluid flow. In the Bouhedma Formation, Northern Chotts Range, Southern Tunisia, although gypsum BPV are clearly observed there is particularly a dearth of published data concerning their characterization. Petrographic examination, tectonic and micro-tectonic analysis of both of the BPV and host rocks were conducted to determine their origin and the formation mechanism of the bedding-parallel fibrous gypsum veins in the Bouhedma Formation. Field studies indicate that the host rocks for the BPV are mostly mudstones and evaporites. The BPV are especially localized within the lower part of the Bouhedma Formation, at boundaries between these sedimentary beds. The deformed gypsum and anhydrite fibers composing the BPV indicate vein growth during the shortening of the basin from the Miocene through Villafranchian times. We argue that the BPV are the result of fluid overpressure and natural hydraulic fracturing in low-permeable sediments due to mineralogical transformations and tectonic compression.