Late Quaternary paleodrainage reconstruction of the Maros River alluvial fan

Abstract The surface of the extensive Maros alluvial fan is densely (0.78 km/km 2 ) covered by paleochannels. The aim of the present study is to reconstruct the final (late Quaternary) stage of the alluvial fan development by identifying paleodrainage directions and determining morphology and pattern of the paleochannels and the age of their activity. On the surface of the alluvial fan, 18 meandering, braided, anastomosing, or misfit paleochannel zones were identified. The existence of these channels indicates that the main process of the fan development was avulsion rather than lateral channel shift, and the overbank floodplain accumulation played a minor role as the paleochannels were not buried. The oldest paleodrainages (A–C) shifted towards north from the east–west-axis of the alluvial fan, draining water to the Koros basin. The similar age (18.7 ± 2.3 ka–14.2 ± 1.4 ka) of the paleochannel zones indicates rapid avulsions or the coexistence of paleodrainages. In the northern half of the alluvial fan, the last large (D) paleodrainage change occurred 12.4 ± 2.1 ka, when the channel turned westward. A large meandering channel functioned for a period (12.4 ± 2.1 ka–9.6 ± 1.3 ka); and with the coexisting misfit channels, these channels drained a considerable amount of water ( Q b  = 2500 m 3 /s). In the next development phase (E paleodrainages), the Maros flowed north; but after a sharp bend, it turned toward the south, and it started to form the southern lobe of the alluvial fan. These channels existed between 8.5 ± 0.9 ka and 3.5 ± 0.4 ka and had a bankfull discharge of 1000–2000 m 3 /s. The last (F) paleodrainage of the Maros River existed for a short time (1.9 ± 0.3 ka–1.6 ± 0.3 ka) and indicated decreasing discharge ( Q b  = 1400 m 3 /s). In the final phase of the alluvial fan evolution, the present-day course of the river was developed, and its discharge decreased further (680 m 3 /s).