Reconstruction of palaeoenvironmental conditions that led to the formation of Eocene sub-bituminous coal seams in the Hungarian Paleogene Basin

Although in the second half of the Eocene, thick sub-bituminous coal seams were deposited in the Hungarian Paleogene Basin, it is not known under what climatic conditions these strata were formed. To investigate this, the paleoenvironmental conditions were reconstructed for the upper Lutetian-middle Priabonian period. The reconstruction of paleoclimatic conditions was based on the Coexistence Approach, for which the climatic data of the extant relatives of 15 fossil plant genera provided the basis of the analysis. Most (87%) of the extant relatives of the studied fossil plant genera can be found most frequently in tropical climate regions. Plotting the reconstructed average mean annual temperature (23.4 ± 3.9 °C) and precipitation (2375 mm ± 964 mm) values to the Whittaker Plot and Peltier's plots it was found that the region had a tropical monsoon climate during the upper Lutetian- middle Priabonian period. At the same time, there was a great difference between the precipitation sums of the wettest and driest months (409 ± 178 mm and 59 ± 56 mm), indicating a tropical monsoon-like climate with strong chemical weathering conditions. Currently, in climatically similar regions, tropical rainforest and tropical moist deciduous forest vegetation grow under tropical rainforest and tropical monsoon climates, and lateritic soils are formed. Furthermore, relatively rich mangrove plant associations flourish along the coasts of these regions, indicating that a part of the peat may have been deposited in mangroves. The contemporary lateritic soils, which later became the protoliths of bauxites, provided a poor nutrient supply for coastal vegetation, likely due to peat accumulation.