The Drmno Basin is characterized by siliciclastic deposition and coal accumulation during the Late Pannonian and Pliocene, which resulted in the formation of numerous coal seams that lack lateral continuity, challenging traditional research methods. The cyclicity and geometry of the coal seams suggest several phases of peat accumulation, interrupted by the influx of siliciclastic material from the Carpathians. Siliciclastic deposition began in the upper delta plain environment and developed into an alluvial plain with river channels and swamps. The coal seams in the Drmno field within the Kostolac open-cast mine show a northward shift of the peat accumulation centre and, together with the coarsening upward trend in the interburden sediments, indicate a south-northward progradation. Biostratigraphic results confirmed the progradation trend with Prosodacnomya carbonifera indicating an age of 7.5–8 Ma in the southern part of the field and with Prosodacnomya elongata indicating an age of 7.2 Ma in the northern part. The influence of recent tectonic activity in the peri-Pannonian domain is reflected by the presence of compressional tectonic structures observed in the basin fill.