Salt tectonics in front of the Outer Carpathian thrust wedge in the Wieliczka area (S Poland) and its exposure in the underground salt mine

Abstract

Salt deposits in the Wieliczka area (Wieliczka Salt Deposit -WSD) in southern Poland comprise saltrich strata belonging to an evaporite succession that originated in the Carpathian Foredeep basin in the Middle Miocene Badenian (Serravallian) times, ca 13.81-13.45 Ma. Although they have been mined since the 13 th century and decades of investigations provided abundant data on their origin and structure, some aspects of their geological evolution are still not fully understood. This study presents current concepts on the lithostratigraphy and tectonics of the WSD.The salt-bearing facies developed near to the southern basin margin, delineated by the Carpathian orogenic front. Such a location triggered the redeposition of sediments and gravity-driven deformation followed by tectonic deformation related to the forelandward advancement of the Carpathian thrusts. As a result, the WSD consists of folds and slices composed of two main salt members: (1) the stratified salt member, with intercalating salt, sulphates and siliciclastics, and (2) the boulder salt member, built of clays with large, isolated blocks of salt. The stratified member contains abundant meso-scale tectonic structures recording the soft-sediment deformation and deformation related to the northward tectonic push exerted by the advancing Carpathian thrust wedge. The boulder member originated due to the syntectonic erosion of evaporites along the basin margins and their redeposition during progressive northward migration of the Carpathian front. Recent interpretations of seismic data imply that the WSD constitutes the core of a triangle zone developed at the contact of the Carpathian orogenic wedge with the backthrust-displaced foredeep sedimentary fill. Meso-scale examples of sedimentary and tectonic structures in the salt-bearing succession exposed in the underground Wieliczka Salt Mine are described and their formation modes discussed.

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

“…The Wieliczka For ma tion re fers to the ha lite-rich ar eas of the Mid dle Mio cene evaporites; where ha lite is ab sent or min imal at the mar gins of the ba sin and on top o graphic highs, the equiv a lent anhydrite-dom i nated evaporites are named the Krzyżanowice For ma tion (Alexandrowicz et al, 1982;Garlicki, 1994). The LES of the Wieliczka For ma tion en coun tered in the mine is il lus trated in Fig ure 5 and de scribed be low (from Wiewiórka, 1979Wiewiórka, , 1988Garlicki, 1979;Ślączka and Kolasa, 1997;Bukowski, 1997;Wiewiórka et al, 2008;Gonera et al, 2012;Burliga et al, 2018;Bukowski et al, 2019). The thicknesses used are pri mar ily from Wiewiórka (1988) but are known to vary re gion ally and even within the mine.…”

“…The mine has also been the sub ject of in ten sive study in more re cent times, with most of the re search de voted to stratigraphic and struc tural as pects (e.g., Tołwiński, 1956;Gaweł, 1962;Poborski and Skoczylas-Ciszewska, 1963;Szybist, 1975;Garlicki, 1979;Wiewiórka, 1979Wiewiórka, , 1988Kolasa and Ślączka, 1985a, b;Tarka et al, 1988;Tarka, 1992;Ślączka and Kolasa, 1997;Bukowski, 1997;Brudnik et al, 2000;Krzywiec and Vergés, 2007;Cyran, 2008;Gonera et al, 2012;Burliga et al, 2018). The Wieliczka Formation is a lay ered evaporite sequence (LES) com pris ing ha lite, anhydrite, and siliciclastic rocks.…”

“…1; cf. e.g., Tarka et al, 1988;Tarka, 1992;Burliga et al, 2018). The or i gin of the de for ma tion is the sub ject of on go ing de bate, with two key as pects still un re solved.…”

“…4 and 6). Most pub lished cross-sections show vari a tions on this theme (Pusch, 1824;Hrdina and Hrdina, 1842;Tołwiński, 1956;Gaweł, 1962;Poborski and Skoczylas -Cisze wska, 1963;Tarka, 1992;Burliga et al, 2018). Se rial sec tions by Gaweł (1962) show that backlimbs are subhorizontal to gently south-dip ping (max i mum ~30°), whereas forelimbs are gen er ally shorter, slightly steeper, and over turned ( Fig.…”

“…1A, B). Fold ing occurs at a va ri ety of scales (met ric to millimetric) in both the weaker halites and stron ger siliciclastics, and in cludes largely har monic folds, disharmonic and polyharmonic folds, and super posed folds; brittle struc tures in clude thrust faults, extensional faults, boudinage, joints, and veins (e.g., Schober, 1750;Pusch, 1824;Gaweł, 1962;Kolasa and Ślączka, 1985b;Tarka et al, 1988;Tarka, 1992;Ślączka and Kolasa, 1997;Cyran, 2008;Burliga et al, 2018). It is of ten as sumed that, since the trends and ven gence of the small-scale struc tures are simi lar to those of the large-scale struc ture, the or i gin is also the orogenic north-vergent thrust ing.…”