Numerical study of tectonic structure evolution in a multi-layer evaporite sequence

Abstract Field studies carried out in the Klodawa Salt Structure (KSS), Poland, reveal that within a carnallite-halite-kieserite sequence, finger-like structures developed during an early, pre-diapiric stage of the KSS evolution. We used 99 numerical simulations to model finger development and investigate mechanical properties of carnallite, halite and kieserite during deformation. Models used inverse density stratification of a three-layer set with varying 1) layer viscosities, 2) thicknesses and 3) density difference ratios. Finger shapes in the models were categorized into single and multiwavelength structures. Among the single-wavelength shapes, bulb, mushroom, thumb and bloated (i.e. without a regular shape) structures were distinguished. We show two transitions between the single and multiwavelength structures, which correspond to the cases of either the lower or upper layer having viscosity more than an order of magnitude larger than the two other layers. Through comparison of finger shapes developed in the models and in the natural structures, we estimate viscosities of >1017 Pa s for halite,