 Sediments were transported to the basin from the uplifting Carpathian and Dinaric mountains, with particularly deep fluvial sediments being deposited in the Pleistocene epoch during the Transdanubian Mountains' formation.Ultimately, up to of sediment was deposited in the basin, and the sea eventually drained through the Iron Gate gorge.The results are large plains in eastern Slavonia's Baranya and Syrmia regions, as well as in river valleys, especially along the Sava, Drava and Kupa.