A new interpretation of the geology of the Włodawa Heights (Western Polesie, eastern Poland)

Abstract

The Włodawa Heights are a morphological elevation composed of Pleistocene deposits located in Western Polesie (eastern Poland). Analysis of the geology of this area based on the type localities of the Mazovian (Holsteinian, MIS 11c) Interglacial allowed the conclusion that it was covered by only two ice-sheets, representing the Sanian 1 and Sanian 2 glaciations respectively (Glacial B, MIS 16 and Elsterian, MIS 12). The elevation was located beyond the range of the Odranian (Saalian, MIS 6) Glaciation. Two horizons of glacial till correlated with the Sanian 1 and Sanian 2 glaciations, and separated by biogenic deposits of the Ferdynandovian (Cromerian III-IV, MIS 13-15) Interglacial, have been distinguished within this elevation in Sosnowica. Deposits of the Sanian 2 (Elsterian, MIS 12) Glaciation are overlain by lacustrine deposits of the Mazovian (Holsteinian, MIS 11c) Interglacial, documented by palaeobotanical studies in sites occurring close to the terrain surface. The sites include: Dobropol B, Suszno (Cegielnia and Scarp), Włodawa Cegielnia, Wyryki, Korolówka, and Ignaców. The lacustrine deposits document a vegetational succession typical of the Mazovian Interglacial. Glacial deposits have not been documented above; in turn, these deposits are overlain by lacustrine deposits of the Liviecian (Fuhne, MIS 10), niveolacustrine deposits of the Odranian (Saalian, MIS 6) and, most commonly, of the Vistulian (Weichselian, MIS 2-5d) glaciations. At most sites, deposits of the Mazovian Interglacial and those overlying them infill palaeotroughs. The Bug River valley was initially also a subglacial trough, which was filled with fluvial and biogenic sediments during the Mazovian (Holsteinian, MIS 11c) Interglacial. Renewal of Bug runoff in the study area took place during the Vistulian (Weichselian, MIS 2-5d) Glaciation. As a megaform, the Włodawa Heights represent an outlier formed due to the erosional activity of fluvioglacial waters during the recession of the Sanian 2 ice-sheet. The form is not an elevation of Cretaceous rocks, because the top of Cretaceous strata to the south of Włodawa Heights in the Leczna-W3odawa Lakeland is located much higher. In the northern part of the Włodawa Heights, minor, NE–SW oriented faults with a throw of 20–30 m, as well as faults with a transverse orientation, have been observed in the Cretaceous rocks. Fracturing of the rock massif, including the development of minor faults, took place during the Alpine deformation events. The geological structure of the Włodawa Heights also does not correspond to the Variscan structural plan, as the area is located within the Włodawa Depression, filled with thick Paleozoic strata and overlain by a succession of Mesozoic rocks which do not display discontinuous deformation.