Vegetation response to environmental changes based on palynological research on the Middle Miocene lignite at the Jóźwin IIB open-cast mine (Konin region, central Poland)

Abstract

Palynological research was performed on the first Mid-Polish lignite seam (MPLS-1) at the Jóźwin IIB open-cast mine. The extremely rich pollen assemblages allowed investigation of the development of phytogenic sedimentation and the succession of plant communities. The vegetation cover, representing peat accumulation and adjacent areas, was reconstructed in the homogeneous lignite seam. Despite the lack of clear macroscopic differences in the lignite lithology and a similar floristic composition, a similar succession of plant communities was observed in three repetitions in the profile. The plant communities described were grouped into five cycles. Changes in the succession resulted mainly from oscillations of the groundwater level. On the basis of the vegetation composition, the climatic conditions predominant during the peat-forming sedimentation were reconstructed. Climate changes are most precisely recorded in the mixed mesophilous forest community. Its floristic composition shows that the climate was warm-temperate and humid at that time. The lower part of the profile contains more taxa with high thermal requirements: Araliaceae, Mastixiaceae, Anacardiaceae, Hammamelidaceae, Cornaceae, Symplocaceae, Ilex, Itea, Engelhardia, etc. It is related to the Middle Miocene Climatic Optimum (MMCO). In the upper part of the profile, the vegetation composition reflects the beginning of a cooling trend. This is indicated by the reduced number of highly thermophilous taxa and the decreased taxonomic diversity of forest communities. The changing climatic and environmental conditions interrupted peat-bog sedimentation and caused termination of the development of thicker lignite seams.