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Late Cretaceous Inversion of the Polish Basin and How It Influenced Its Petroleum System

Abstract

The Permian-Cretaceous Polish Basin belonged to the system of epicontinental depositional basins of Western and central Europe and was filled with several kilometers of siliciclastics, carbonates, and also thick Upper Permian evaporites in the central and N parts of the basin. The basin underwent three major pulses of increased subsidence rates during the Zechstein–Scythian, Oxfordian–Kimmeridgian and early Cenomanian, and was fully inverted in Late Cretaceous–Palaeocene, when its most subsiding axial part, the Mid-Polish Trough, was transferred into the regional anticlinal structure, the Mid-Polish Swell. Wealth of the high-quality seismic data, including new data acquired during exploration for unconventional hydrocarbons and regional high-end PolandSPAN survey, allows painting comprehensive picture of the Polish Basin present-day structure and its Mesozoic evolution. Turonian – Maastrichtian compressional inversion of the Polish Basin was complex and multi-phase. It involved uplift of various basement blocks and compressional reactivation of salt structures. Growth of inversion-related salt and non-salt structures resulted in modification of the depositional systems characterized by localized thickness variations and progressive unconformities. Seismic data from the northern (Pomeranian) segment of the basin prove that marginal troughs presently located along flanks of the Mid-Polish Swell, had not been formed as a relatively narrow structure filled up with the syn-kinematic inversion-related Upper Cretaceous deposits, as it was previously assumed. 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. Southern segment of the basin, mostly devoid of the Permian evaporites, is characterized by presence of various inversion structures directly rooted within the pre-Permian basement. They include basement blocks uplifted along the reverse faults; strike-slip movements were also involved, including latest Cretaceous – Paleogene wrenching along the Grójec Fault Zone, very deeply rooted in the Precambrian basement. Inversion of the Polish Basin created numerous anticlinal structures that could have acted as traps for hydrocarbons. However, earlier (pre-inversion) generation and migration of hydrocarbons did not allow for their entrapment.