Post-pleniglacial floodplain sediments in Central Belgium

Abstract

This paper presents an outline of the floodplain sediments which dominated the river environment during the last 13,000 years in the western parts of Central Belgium. It is based on literature, with special reference to the Mark River basin. River landscapes and related floodplain sediments are a combined result of changing external factors such as climate and human activity, and prevailing local geological and topographical conditions. The development of the vegetation predominantly controls the sediment and water fluxes in the catchment. After the Pleniglacial, a system of palaeovalleys developed as a result of a non-equilibrium between vegetation and climate. For more than 10,000 years, this system dominated the river landscape, while gradually being filled with organic material and sediments. Three infilling phases can be distinguished: the Gully facies, the Organic and tufa facies, and the Fluvial clay facies. The Gully facies reflects an initial time period of fluvial activity, and occupies the lowermost parts of the palaeovalley. From 9000 BP onwards, forest swamps occupied the river plains, reflecting very stable conditions in the catchments. The Organic and tufa facies was formed. During the second half of the Atlanticum, from about 6000 BP onwards, human agricultural activities greatly affected the river landscape and the hydrological system. The forest swamps disappeared and were gradually replaced by open water. The deposition of the Fluvial clay facies concluded the filling of the palaeovalley. Medieval clearings in the catchments, less than 1200 years ago, disrupted the originally stable hydrological regime of the river. The Surface loam facies was deposited during inundations, independent of the palaeovalley system.