Decline of Neogene lignite formation as a result of vegetation and climate changes reflected in the middle Miocene palynoflora from the Ruja lignite deposit, SW Poland

Abstract

The paper presents results of a palaeobotanical investigation of the borehole core Komorniki 97/72 from the Ruja lignite deposit, Lower Silesia. In the deposit lignites of three (2nd Lusatian, 2nd A Lubin, and 1st mid-Polish) middle Miocene groups of seams are present. The lignites of the 1st and 2nd groups are important correlation horizons throughout much of the Polish Lowlands and eastern Germany. The results of the palynological studies (spore–pollen, algae and fungi) and plant macroremains studies show that during the mid-Miocene mires' development, the vegetation was characteristic of wetlands (i.e., swamp and riparian forests, shrub bogs, and reed marshes) as well as mesophytic forests. The results were also used for palaeoclimatic investigation. The mean annual temperature (MAT), for each of the three sections, based on the coexistence approach (CA) method, was estimated in the range of 15.7–17.8 °C. Nevertheless, the frequency of thermophilous (palaeotropical and palaeotropical/warm-temperate) taxa indicate climate changes during the formation of the studied sediments. Composition of the spore–pollen spectra from the 2nd Lusatian seam (i.e., the presence of Meliaceae and Sapotaceae, which currently have pantropical distribution) show that the climate was humid and warm, close to subtropical. Later, many palaeotropical taxa disappeared, and the composition of the spore–pollen spectra indicates a warm temperate climate with slight fluctuations. Above the 1st mid-Polish seam, the climatic conditions changed in a way that did not favor the further formation of lignite deposits. These results correspond with the current understanding of climate change in the middle Miocene in Europe.