Lithological diversity of the deposits of closed depressions in central Poland as a result of their origin conditions

Small closed-drainage depressions are a common element of the landscape of Central Poland. Their origin is mainly connected to the melting of blocks of dead ice in the phase of advanced recession of the ice-sheet in the Wartanian Stadial of the Odranian Glaciation. In the Łódź Upland, an analysis of four sites containing sets of depressions has been conducted to determine the lithological properties of their infillings. The analysis revealed that the frequently deep, steep-walled basins are filled in with deposits of various age and origin. Four lithological units, containing sediments ranging from a glacial base to the mineral sediments of the Vistulian, were formed. Many of the depressions do not contain biogenic sediments of the Eemian Interglacial. The lithological suggestions of the age of the deposits allowed to determine two types of depressions - fossil depressions of melting origin, and genetically complex ones that underwent deposition prior to the Eemian Interglacial and with a secondary deepening, most likely as a result of melting of ground ice under thermokarst conditions, during the Vistulian Glaciation (=Weichselian). The dominant views that connect the origin of the multiple depressions solely to the end of the Wartanian should be verified.