Palaeoenvironmental evaluation by geochemical proxies of fluvio-lacustrine core log from the Late Miocene-Pliocene Maritsa Iztok Basin, Bulgaria

A sequence of three lignite seams and interlayering carbonaceous mudstone is characterized by geochemical proxies. The study is extended by the palaeoenvironmental details given by the fossil fauna (gastropods, ostracods, and fishes). The predominant minerals (quartz and kaolinite) and main oxide relations of the carbonaceous mudstone point to sand and clay washed from weathered and/or altered felsic rocks from the catchment area. The mudstone features to deposition from suspension in standing or slow to persistently moving fresh waters at the bottom of the core log, and slightly aerated, warm, fresh to low saline, acidic to alkaline waters on the top. Three communities of organisms are depicted. The first is the pre-swamp environment characterized by standing or slow moving fresh waters and detrital organic matter deposition. The second is the environment of swamp of detrital forest trunks. Depending on the climate and water table, the main forest communities are of trees of families Cupressaceae, Taxodiaceae, and Podocarpaceae accompanied by trees of family Betulaceae, and herbaceous plants. Different Sphagnum species are also abundant. The dry/cold environment is reflected in the herbaceous organic matter deposition. Polar terpenoids ratio differentiates slight climatic oscillations for the samples with a strong Gymnospermae dominance. The second coal seam development reflects the optimum tectonic conditions for peat growth in a cold and dry climate leading up to 25 m lignite deposition. The third is the moss swamp environment with very fluctuating elements. At the top of the log, a Sphagnum-dominated peat has developed.

Automated summary

The study examines a sequence of three lignite seams and interlayering carbonaceous mudstone, using geochemical proxies and fossil fauna analysis to characterize pre-swamp, swamp, and moss swamp environments, as well as variations in climate conditions.