Late Pleistocene – Holocene fluvial landforms of the Maros River Alluvial Fan

Abstract

The surface of the extensive Maros/Mures Alluvial Fan is densely (0.78 km/km2) covered by palaeo-channels. The aim of the present study is to determine the direction of the river-courses, the channel morphology and OSL age distribution of the palaeo-channels, and to reconstruct the final period of the development of the alluvial fan.
On the surface of the alluvial fan, 18 palaeo-channel zones were identified; their channel pattern is meandering, braided, anastomosing or misfit. The existence of these channels indicates that the main process of the fan development
was an avulsion rather than a gradual lateral migration and overbank floodplain accumulation. The oldest palaeochannels (18.7±2.3 ka – 14.2±1.4 ka) shifted towards the north from the EW-axis of the alluvial fan, draining water to the Körös Basin. The similar age of the palaeo-channel zones indicates rapid avulsions and river course changes, or the coexistence of palaeo-channels. In the northern part of the alluvial fan the last river-course change happened ca. 12 thousand years ago, when the channel turned slightly southwards. The huge meandering channel (12.4±2.1 ka – 9.6±1.3 ka) and the coexisting misfit channels drained a large amount of water (Qb=2500 m3 /s). In the next development phase the Maros ran northwards, but after a sharp bend it turned towards the south and started to form the southern lobe of the alluvial fan. Approximately 8.5±0.9 ka – 5.3±0.8 ka ago the coexisting channels had a large bankfull discharge (1000-2000 m3/s). The last palaeo-course of the Maros River dates back to 1.9±0.3 ka, indicating decreasing discharge (Qb=1400 m3 /s) at the end of the Holocene. In the final phase of the evolution of the alluvial fan, the present-day course of the river was developed and its discharge dropped even further (680 m3/s).