Secondary minibasins in orogens: Examples from the Sivas Basin (Turkey) and the sub-Alpine fold-and-thrust belt (France)

Inherited and syn-compressional salt-controlled structures in orogens are difficult to distinguish from compressional features because classical salt features (halokinetic growth strata, salt welds) can be misinterpreted as shortening-related structures (syn-kinematic growth strata, tectonic unconformities). In the Sivas basin in Turkey, syn-kinematic salt diapirism entirely shaped the architecture of the foreland and allowed the development of primary and secondary minibasins. One of the most impressive, the Tuzlagözü minibasin, formed by sinking into a salt feeder while being upturned due to compression. This minibasin has been nicknamed the “Turkish Vélodrome” because of its similarity with the well-known Vélodrome structure in the French Alps which shows growth strata and successive unconformities, commonly interpreted as foreland growth syncline features. Based on structural field descriptions and geometric analogies with the Tuzlagözü minibasin, we revisit the Vélodrome as a salt-related minibasin. We argue that the Vélodrome developed as a secondary minibasin above an Oligocene aerial salt glacier: sheet of Upper Triassic evaporites extruded during Alpine orogeny. This new interpretation enables to propose a revised evolution of the sub-Alpine fold-and-thrust belt. In line with other recent works, this study emphasises once again the important role of salt tectonics in the evolution of the sub-Alpine fold-and-thrust belt.