Triassic evolution of the Kłodawa salt structure: basement-controlled salt tectonics within the Mid-Polish Trough (Central Poland)

The Mid-Polish Trough formed the axial part of the Polish Basin belonging to a system of the Permian-Mesozoic epicontinental basins of Western and Central Europe. It was filled by several kilometres of siliciclastics and carbonates, including thick Zechstein (approximately Upper Permian) evaporites. TheMid-Polish Trough was inverted in the Late Cretaceous-Paleocene times, when it was strongly uplifted and eroded. The presence of thick salt significantly influenced Triassic evolution of the central (Kuiavian) part of theMid-Polish Trough where the Kłodawa salt structure is located. Analysis of seismic data calibrated by several deep wells point to three main stages of the Triassic evolution of this structure. During Early andMiddle Triassic Kłodawa salt pillow grew above the basement extensional fault zone, during early Late Triassic (approx. time of deposition of the Lower Gypsum Beds) Kłodawa salt structure reached diapiric stage and salt eventually extruded on to the basin floor. Last stage was characterised by rather uniform sedimentation and lack ofmajor saltmovements. Wojszyce salt pillow located north-east of the Kłodawa salt structure grew until the Late Triassic (approx. time of deposition of the Upper Gypsum Beds) when basement fault zone located below it was probably inverted. This inversion triggered formation of the salt-cored Wojszyce Anticline and was followed by localised erosion and rather uniform Norian–Rhaetian (Lower Kłodawa Beds) sedimentation above the anticline. Local tectonic activity below the anticline might have additionally enhanced growth of the Kłodawa salt diapir. The presented tectono-sedimentary model of the relationship between basement and salt tectonics and their influence on the Triassic depositional systems is compatible with results of analogue modelling of linked basement-salt tectonics, and with a model based on mesostructural studies completed for the Kłodawa salt mine.