Nature and origin of large-scale and intrasalt deformation within the Wieliczka salt mine, Poland

The Wieliczka salt mine, near Kraków in southern Poland, is a world-famous historical and modern destination for both geoscientists and tourists. Despite numerous publications, there is still a lack of consensus on the nature and origin of the large-scale folds as well as whether the small-scale structures represent tectonic or soft-sediment deformation. In this preliminary work, we offer new ideas on both aspects. At the large scale, we emphasize the mechanical stratigraphy of the layered evaporite sequence, which comprises a thin basal weak layer, a thin strong unit, a thicker weak layer, and a thicker strong unit. We suggest that the inclined to recumbent folds and thrusts formed tectonically due to over thrust shear between the basal detachment and the overriding Carpathian frontal thrust, with different structural styles decoupled by the thick weak layer. At the small scale, we suggest that there was early extension directed toward the east to north-east, followed by contraction vergent toward the north. We infer that there was early, syndepositional gravity gliding down a topographic slope dipping into the coeval Gdów depocenter to the east, and that subsequent north-directed Carpathian shortening generated the small-scale contractional structures as the larger folds were developing.