Milankovitch-scale multi-proxy records from fluvial sediments of the last 2.6 Ma, Pannonian Basin, Hungary

The continuous cores of two nearly 500 m deep boreholes, cutting Pleistocene fluvial sequences in the eastern part of the Pannonian Basin, Hungary have been studied. Magnetostratigraphy indicates that the sediment sequences span the last 2.6 Ma without significant hiatuses. Comparison of systematic variations in magnetic susceptibility with changes in grain size distribution revealed Milankovitch-scale cyclicity in sedimentation of 40 and 100 kyr cyclicity, which also shows a correspondence with the delta(18)O variations of the ODP 677 site. Comparison of pollen and gastropod paleoecological data with the magnetic susceptibility proxies suggests that climate was a major allogenic control on the cyclicity. Zones of high magnetic susceptibility correspond closely with sandy and coarse silty parts of the borehole successions which largely coincide with pollen and molluscs indicating a warm climate. On the contrary zones with low magnetic susceptibility correspond to silts and clays, and in most cases coincide with cold climate indicator pollen and molluscs. Heavy mineral and XRD studies revealed that magnetic susceptibility reflects the absolute amount of detrital Fe-oxide minerals, mostly magnetite. Variations in the amount of magnetite are related to changes in heavy mineral content, which arise primarily from changes in sediment supply to the basin by rivers. The depositional model for the Pleistocene fluvial sediments suggests that sediment flux increased towards the basin during interglacials, due to the increased discharge and transport capacity of the rivers, while a decreased sediment supply to the distal parts of the basin occurred during glacials. A delay between erosion and storage of weathering products near to the source area and subsequent transportation and re-deposition of sediments in the basin interior setting is an important cause of this effect. (C) 2003 Elsevier Science Ltd. All rights reserved.