The palynology of late Miocene sinkhole deposits from Upper Silesia, Poland

•Deposits from a paleosinkhole at Górażdże, SW Poland were analyzed palynologically.•Pollen, spores of plants and organic-walled algal remains assemblage from the infill were studied.•The fossil freshwater algae community and vegetation were “reconstructed”.•The results indicate that the infill was deposited in the late Miocene.•The karst development and development of open landscape problems were discussed.

This paper presents the results of a palynological investigation of an assemblage of pollen, spores and organic-walled microalgal remains from the paleosinkhole infill exposed at Górażdże, Upper Silesia, SW Poland. The results of previous palynological studies indicate that the infill was deposited in the late Miocene, probably during the more humid Tortonian stage.The sinkhole at Górażdże was filled with shallow water that periodically might have dried out or, at least, undergone seasonal warming. Green algae (Chlorophyta) such as Zygnemataceae, Botryococcus and Pediastrum, as well as Sigmopollis were major components of the algal community. The presence of planktonic algae Pediastrum and Tetraedron as well as pollen grains of aquatic plants, such as Nuphar and Nymphaea, indicate that there were extended periods of standing water. The pond was surrounded by vegetation composed of herbs and riparian forests dominated by Alnus, Salix, Ulmus, Pterocarya, Carya, and others. More dry terrains were presumably covered by mixed forests composed of Pinus, Tsuga, Picea, Quercus, Carpinus, Fagus, Betula, and others, with only a small admixture of thermophilous plants, such as Castanea. Ericaceae were presumably a component of the groundcover of the forests, or they formed their own open dwarf-shrub communities, such as bush swamps or heathlands. A high frequency of Poaceae pollen grains might reflect the development of open landscapes. The climate during the deposition of sediments in the sinkhole was warm temperate and mild, without severe winters.A comparison of the sporomorph association from the studied sinkhole with another Neogene paleosinkhole palynoflora from the neighboring Tarnów Opolski site revealed asynchronous karst development in the western part of the Upper Silesian Upland, with the infill sediments being at least middle and late Miocene in age.