Phases of Palaeogene and Neogene tectonic evolution of selected grabens in the Wielkopolska area, central-western Poland

Fazy paleogenskiego i neogenskiego rozwoju tektonicznego wybranych rowow na obszarze Wielkopolski In the Wielkopolska (Great Poland) area, there occur numerous tectonic grabens which were active in the Palaeogene and Neogene. The similarities and differences between their development are presented on the example of the Czempin, Szamotuly, Lubstow, and Wladyslawow Grabens. Using various methods of palaeotectonic analysis, the stages of accelerated subsidence of the grabens, i.e. tectonic phases, were indicated. The extent of vertical movement in the studied grabens were compared and it was affirmed that there is a connection between the occurrence of older dislocations and salt structures in the deep basement. From among the examined grabens, the Lubstow Graben is the deepest one, and shows the most complex geological structure. The Czempin and Szamotuly Grabens are characterized by relatively simple geological structure, where the stratigraphic completeness and tectonic style are very legible. These three grabens were active in different tectonic stages from the turn of the Eocene/Oligocene till the end of the Neogene, and perhaps also in the Prepleistocene. The Wladyslawow Graben is a very shallow tectonic structure and its evolution lasted for the shorter period of time. The time of its development extended from the Early through the Middle Miocene. These grabens provide a good example of the relationship between the fault throw and graben location. The Czempin, Szamotuly, and Lubstow Grabens, connected with deeply-rooted dislocations, came to existence in the Pyrenean phase (latest Eocene - Early Oligocene). However, the Wladyslawow Graben was affected mainly by salt structure activity. Thus, its first stage of tectonic evolution took place in the Savian phase (Early Miocene).