Acta Geologica Polonica, Vol. 69 (2019), No. 3, pp. 387–401 DOI: 10.24425/agp.2019.126439 Paleogene–Neogene tectonic evolution of the lignite-rich Szamotuły Graben MAREK WIDERA 1, *, WOJCIECH STAWIKOWSKI 1 and GRZEGORZ UŚCINOWICZ 2 1 Institute of Geology, Adam Mickiewicz University, 12 Krygowski Street, 61-680 Poznań, Poland. E-mails: widera@amu.edu.pl; wojst@amu.edu.pl 2 Polish Geological Institute-National Research Institute, Marine Geology Branch, 5 Kościerska Street, 80-328 Gdańsk, Poland. E-mail: gusc@pgi.gov.pl *corresponding author ABSTRACT: Widera, M., Stawikowski, W. and Uścinowicz, G. 2019. Paleogene–Neogene tectonic evolution of the lignite- rich Szamotuły Graben. Acta Geologica Polonica, 69 (3), 387–401. Warszawa. The Szamotuły Graben covers the southernmost part of the Permo-Mesozoic Poznań–Szamotuły Fault Zone. Along this regional discontinuity there are several salt structures, including the Szamotuły diapir, over which an extensional graben formed in the Paleogene and Neogene. The graben is located north of Poznań in cen- tral-western Poland, and is NW–SE-trending, ~20 km long, 3–5.5 km wide, and up to 160 m deep. It is filled with Lower Oligocene and Neogene sediments, including relatively thick lignite seams. Data from boreholes allow the assignment of the graben-fill sediments to appropriate lithostratigraphic units. Furthermore, analy- sis of changes in the thickness of these units provides evidence for periods of accelerated graben subsidence or uplift relative to its flanks. As a result, two distinct stages of tectonic subsidence and one inversion in the Paleogene–Neogene evolution of the Szamotuły Graben have been distinguished. Thus, relatively significant subsidence occurred in the Early Oligocene and the middle Early–earliest Mid-Miocene, while slight inversion took place in the middle part of the Mid-Miocene. Key words: Palaeozoic Platform; Polish Basin; Salt diapirism; Syn-sedimentary tectonics; Lignite compaction. INTRODUCTION The Szamotuł y Graben forms part of a fault-re- lated fold zone (Text-fig. 1). This regional-size tec- tonic zone is referred to in a great variety of ways in the geological literature. From the point of view of pre-Cenozoic tectonics, for example, it is referred to as the Drawno–Człopa–Szamotuł y Zone (Leszczyński 2002); the Drawno–Człopa–Szamotuł y salt struc- ture system (Krzywiec 2006); the Drawno–Poznań Fold-and-Fault Belt (Żelaźniewicz et al. 2011); and the Grzęzno–Człopa–Szamotuł y Zone (Leszczyński 2012). On the other hand, taking into consideration the Cenozoic tectonic activity, it may be referred to as the Poznań–Szamotuł y Dislocation Zone (Deczkowski and Gajewska 1980; Kasi ński 1984, 1985; Kwolek 2000; Widera 2004; Widera et al. 2004; Widera and Karman 2007) or the Poznań–Szamotuł y Fault Zone (Text-fig. 1; Widera et al. 2008; Widera and Hał uszczak 2011). We analyse herein the area between Szamotuł y and Poznań where Paleogene–Neogene vertical movements were particularly marked, and therefore, the name of Poznań–Szamotuł y Fault Zone will be used throughout this paper (Text-fig. 1). In contrast, the salt diapir, the Cenozoic graben and the lignite deposit filling it have the same locality name, that is, the Szamotuł y salt structure (Krzywiec 2006), Szamotuł y salt diapir (Rowan and Krzywiec 2014), Szamotuł y Graben (Widera 2004, 2007, 2016a), and