Original paper

Late Cretaceous inversion of the NW segment of the Mid-Polish Trough – how marginal troughs were formed, and does it matter at all?

Krzywiec, Piotr; Stachowska, Aleksandra

Abstract

Inversion of sedimentary basins leads to uplift of the basement blocks together with their sedimentary cover formed during earlier phases of basin's development. Such inversion-induced uplift is related to more or less extensive erosion and redeposition, leading to the formation of synkinematic, syninversion sedimentary cover that accumulates in local depressions (marginal troughs) that flank inverted and uplifted parts of the basin. The Permo-Mesozoic Polish Basin was inverted in Late Cretaceous to Palaeocene times. Its most subsiding axial part, the Mid-Polish Trough, was uplifted and transformed into the regional anticlinal structure, the Mid-Polish Swell. Regional thickness maps of the syninversion sequence show prominent elongated thickness maxima located along the flanks of the Mid-Polish Swell. Such a regional thickness distribution was used by Nielsen et al. (2005) to propose a new model of the Alpine inversion in Central and Eastern Europe, with the early (Late Cretaceous) phase of inversion related to increased intraplate compressional stresses, and the late (Palaeocene) phase related to a plate-wide relaxation of intraplate compressional stresses. Interpretation of a relatively dense coverage of seismic reflection profiles located above the SW edge and flank of the NW segment of the Mid- Polish Swell (Drawno-Cz ł opa system of salt structures and its surroundings) provided detailed information on the internal geometry of the marginal trough filled up by the Upper Cretaceous sedimentary succession and formed during inversion of this segment of the Mid-Polish Swell. It was proved that this marginal trough had not been formed as a relatively narrow structure filled up with the syn-kinematic inversion-related Upper Cretaceous deposits. Instead, the Upper Cretaceous cover must have been much more extensive and its present-day map distribution showing elongated thickness maxima located along the flanks of the Mid-Polish Swell is the result of the latest phases of inversion-related uplift, folding and erosion, and salt tectonics. Therefore, it should not be used to support a model of two-phase regional inversion proposed by Nielsen et al. (2005) with its first phase intrinsically related to the formation of narrow and elongated marginal troughs.

Keywords

late cretaceousmid-polish swellsalt tectonicsmid-polish troughmarginal troughsinversionpolish basin