Numerical study of tectonic structure evolution in a multi-layer evaporite sequence. (May 2020)

• Record Type: Journal Article
• Authors: Słotwiński, Michał; Adamuszek, Marta; Burliga, Stanisław
• Is Part Of: Journal of structural geology. Volume 134(2020)
• Publication Date: 2020-05
• Subjects: Rayleigh-Taylor instability -- Finger structures -- Viscous deformation -- Rheological properties of evaporites -- Kłodawa salt structure -- Numerical modelling; Geology, Structural -- Periodicals; Géomorphologie structurale -- Périodiques; Geology, Structural; Periodicals; 551.805
• DOI: 10.1016/j.jsg.2020.104011
• Languages: English
• ISSNs: 0191-8141

Abstract

Abstract: Field studies carried out in the Kłodawa 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 >10 17 Pa s for halite, <10 17 Pa s for carnallite and <10 16 Pa s for kieserite. The estimated low viscosity of kieserite can be attributed to the small grain size of the rock, the presence of fluids during deformation or to different mineral composition of the layer than presently observed. Graphical abstract: Image 1 Highlights: Elongated finger-like evaporite structures were observed in Kłodawa, Poland. Structures were interpreted as originating from Rayleigh-Taylor instability. 2D FEM was used to produce numerical analogues of the structures. Order of increasing viscosity was revealed as kieserite-carnallite-halite. Absolute viscosity values were constrained by analysis of time-span deformation.