Salt tectonics versus delamination of the supra-salt cover during extension and compression – 3D geometry and Mesozoic evolution of the Goleniów salt structure, NW Poland

The Goleniów salt structure (GSS) is located in the NW part of the Polish Basin which belongs to a system of Permian-Mesozoic epicontinental sedimentary basins of the Western and Central Europe. Its axial part (so called Mid Polish Trough – MPT) was filled with several kilometres of sediments, mainly siliciclastic and carbonates but also with Zechstein (Upper Permian) evaporites. The Polish Basin was fully inverted in Late Cretaceous-Paleogene. The presence of thick layer of evaporites led formation of diverse salt structures. The study area is located within the SW flank of the MPT, characterized by presence of numerous salt and salt-related structures. One of them is NNW-SSE oriented Goleniów structure which extends over 25 km with the salt diapir (salt wall) in its NNW part. Interpretation of the dense array of 2D seismic reflection profiles allowed for the construction of the 3D model of the GSS and assess its spatial evolution including significant role of delamination of the supra-salt Mesozoic sedimentary cover during both extension (basin subsidence) as well as compression (basin inversion).

NNW part of the Goleniów structure is formed by a well-developed salt diapir (salt wall). Its evolution started in Late Triassic when regional extension triggered formation of the asymmetric reactive diapir. After Late Triassic-Early Jurassic active piercement, diapir continued its growth as a passive diapir due to a regional extensional tectonic regime. In Middle and Late Jurassic, insufficient amount of salt in the source layer led to diapir burial. Further extension caused diapir to fall. This resulted in Early Cretaceous localised extension within the crestal part of the diapir and formation of a half-graben filled with Lower Cretaceous sediments of increased thickness. The Goleniów structure was significantly re-shaped during Late Cretaceous inversion of the Polish Basin. GSS was rejuvenated and started to growth which led to roof uplift and its partial erosion. This progressive compression-related Late Cretaceous growth is very well documented by growth strata preserved above the diapir. Finally, after completion of inversion of the Polish Basin, salt crest reached in Cenozoic groundwater active circulation zone which in turn caused its dissolution and eventually development of the dissolution-collapse trough filled with Cenozoic sediments with increased thickness.

The style of the deformation alongstrike changes toward the SSE where, due to smaller amount of evaporites salt diapir did not form and was replaced by a complex zone of thin-skinned deformation detached within Zechstein evaporites. First, thin-skinned half-graben was formed during Late Triassic-Early Jurassic extensional phase. It was then compressionally reactivated during basin inversion and this led to enhanced delamination and then thrusting within the Upper Triassic (Keuper) section. Complex backthrusting and local wedging was related to formation of a secondary detachment level within Keuper evaporites and resulted in formation of "fish tail" structure. Backthrusting was associated with substantial folding of hangingwall strata.