Millennial-scale climatic fluctuation in the fluvial record during MIS3: Very high-resolution seismic images from NE Hungary

• Meander migration in MIS3 is reconstructed by variations of point bar geometry.
• Channel-forming discharge is calculated from the ancient width and depth data.
• Millennial scale discharge fluctuations are superimposed by even smaller ones.
• Primary trend is reflected by long-term incision and infilling of the river channel.
• Stepwise incisions, meander development changes are related to high-discharge events.

Alluvial architectures of a meandering river existing in MIS3 were observed on very high-resolution (VHR) single-channel waterborne seismic profiles, 20–30 m below the Tisza River in the Pannonian Basin (Hungary). The study investigated the spatial and temporal variations of two, more than 2 km-long continuous series of inclined reflections interpreted as laterally accreted point bar complexes. The phases of natural meander migration were reconstructed in 3D based on the changes in the geometry and dip of the inclined reflections. A channel-forming discharge curve extending over approximately 2.5 ky was calculated by using paleo-width and depth data derived from the lateral accretion surfaces.Systematic analysis of the geometrical variations coupled with the discharge curve evaluation on each point bar complexes indicates millennial-scale discharge fluctuations 40–50 ky ago, to that the river responded principally by incision and infilling. The primary periodicity, comparable to the sub-Milankovitch cycles, is superimposed by shorter periods: ca. 500-year cycles reflect the phases of unidirectional meander development, while the smallest ones reflect the recurrence interval (150–200 years) of the highest floods. River-bed incisions happened step-by-step related to extreme floods, when the meander development also changed. The smaller-scale and more rapid fluctuations within a development unit were represented in variations of the channel width. Although the poor geochronology of the sandy fluvial deposits cannot allow any direct correlation to the climatostratigraphic events, the millennial-scale climate variations of MIS3 were pronouncedly characteristic in the discharge fluctuations.