Late glacial river-bed changes on the Little Hungarian Plain,based on preliminary chronological, geological andpaleontological data

Abstract

Comprehensive chronological, geological andpaleontological investigations were conducted as part ofarchaeological excavations in 2011 and 2012, prior to theconstruction of the M85 motorway between Gyor andCsorna, Hungary. These studies clearly show that the alluvialfan that underlies much of the Little Hungarian Plainwas built up by streams flowing in a southeasterly to northwesterlydirection from the nearby Bakony Hills, and continuedto form until the end of the last glacial period. Thenorthern part of the fan, now named the Csorna Plain,became inactive (i.e. became a fossil river-bed system) atabout 25–15 ka, when the Rába and Marcal rivers changedtheirflowdirection fromsouth–north towest–east.As a resultof this change in flow direction, the Rába and Marcalrivers became incised, capturing the Bakony stream beds,stopping sediment deposition on the northern side of thealluvial fan (essentially the left bank of the Rába-Marcalriver system), although the southern part of the fan continueto form as before. On the northern side of the fan, thesediment surface dried out due to falling groundwater levels,and aeolian sand-drifts began to form. Eventually, accumulationof the sand-drift sediments ceased due to thedeposition of loess-type sediments, which fixed the surface,conserved the sand-drift shapes, and contributed tothe straightening and eventual canalization of the fluvialchannels. Geoarchaeological examinations indicate thatthe development of present fluvial features were stronglyaffected by the settlement and tillage activity of humancommunities on the Csorna Plain.

Keywords

• little hungarian plain
• river capture
• csornaplain
• fossil river-bed