RELATIVE SEA-LEVEL FLUCTUATIONS AND BROWN-COAL FORMATION AROUND THE EARLY MIDDLE MIOCENE BOUNDARY IN THE LUSATIAN BROWN-COAL DISTRICT

The Tertiary sedimentary sequence in the Lusatian Brown Coal District is the result of several transgressive pulses with intercalated regres sive phases. Regression repeatedly resulted in the formation of large littoral bogs at the transition between brackish and terrestrial palae oenvironments. In the lithofacies changes of the Lower - Middle Miocen e strata (high energy sands, low energy intertidal silts, paralic peat s) long-term changes as well as short-term oscillations of sea level a re recorded. The rise of sea level in the upper Lower Miocene (Hemmoor ian transgression) is proved in numerous localities of the investigati on area. After a regression phase with major peat formation events aro und the Lower - Middle Miocene boundary, a renewed sea-level rise resu lted in the widest extension of marine - brackish beds over pre-Tertia ry basement in the south of the region (higher Reinbekian transgressio n, Middle Miocene). Very differentiated, fine-scaled, probably sea-lev el induced coastline oscillations could probably be traced even into t he coal seams by the recognition of successive bogfacial types possibl y showing a groundwater level change in the ancient peat bog (change o f topogeneous and ombrogeneous bog types). A biostratigraphic calibrat ion of the decalcified Lower-Middle Miocene sequence with its alternat ing transgressive and regressive trends to the fully marine sediments of the basinal centre, which are dated by calcareous microfossils, is possible by means of dinoflagellate cysts and pollen and spores.