Middle Miocene aquatic and wetland vegetation of the paleosinkhole at Tarnów Opolski, SW Poland

Abstract

I analyzed spores, pollen and organic-walled algal remains in Middle Miocene deposits that filled a paleosinkhole at Tarnow Opolski, in the Upper Silesian Upland, Poland. Middle Triassic limestone bedrock in the study area underwent intense karstification under relatively warm and humid climate, resulting in development of numerous sinkholes. As the corrosion reached non-karstified marls, flowing water in the vadose zone was plugged and meteoric waters thus accumulated, leading to pond development. This palaeobotanical study was undertaken to “reconstruct” the fossil freshwater algae community and vegetation in and around the water body. Chlorophyta such as Botryococcus, filamentous algae from the family Zygnemataceae, mainly Mougeotia, Spirogyra and Zygnema, and desmids were important components of the algal assemblage. Most of the identified algae prefer mesotrophic to eutrophic conditions, and are characteristic of stagnant or slow-flowing shallow water. Among the free-floating and rooted plants were Salviniaceae/Azollaceae (probably Salvinia), Nuphar, Potamogeton, and carnivorous taxa such as Utricularia and probably Aldrovanda. The water body was surrounded by swamp vegetation composed of herbs such as Typha, Sparganium, Alismataceae and others, and riparian forests. The upper portion of the sediment section contains abundant pollen of swamp forest taxa such as Taxodium/Glyptostrobus, Nyssa and Alnus. The paleobotanical remains from the sinkhole at Tarnow Opolski suggest it was a shallow water body that was probably prone to rapid warming. Presence of resting cells, e.g. zygospores of Zygnemataceae and desmids, suggests that the pond may have dried periodically. Presence of Nuphar, Utricularia and Aldrovanda pollen, however, indicates long periods with standing water.