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1 Geological Quarterly

1 2002

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Palaeotectonic cross-sections through the Mid-Polish Trough

Wagner R., Leszczyński K., Pokorski J., Gumulak K.

Geological Quarterly

2002

Vol. 46, No 3

293-306

The Late Permian and Mesozoic evolution of the Mid-Polish Trough is analysed using a set of palaeotectonic cross-sections which are constrained by regional integrated depth-converted reflection seismic profiles. Results support the concept that the central and NW part of the Mid-Polish Trough can be subdivided into a Pomeranian and a Kuiavian segment. The Pomeranian segment is characterised by lower subsidence and a shallower depth to the base of the Zechstein (3500-4000 m) as compared with the Kuiavian segment. The Pomeranian basin was characterised by a nearly symmetrical structure and a single depocentre. In Kujawy, the basin displays a more complex structure with several local depocentres. In the Pomeranian segment, salt structures are poorly developed (salt pillows). These formed relatively late: during the latest Cretaceous and Early Paleocene. In the Kuiavian segment, salt structures include also salt diapirs which began to form at the end of the Muschelkalk, and were active later throughout Mesozoic times, as evidenced by lateral facies and thickness changes. During end Cretaceous and Paleocene basin inversion, the base of the Zechstein was uplifted by 3000-4000 m in the Kuiavian segment and by 2000-3000 m in the Pomeranian segment. The transition zone between the Pomeranian and Kuiavian segments, located in the area between Piła and Toruń, displays mixed features in its structure and geological evolution. Subsidence of the Mid-Polish Trough was controlled by multiple extensional pulses during which pre-existing crustal-scale faults were reactivated. Similarly, inversion of the Mid-Polish Trough involved reactivation of crustal faults. Segmentation of the Mid-Polish Trough can be related to factors including differences in its basement composition.