Holocene floodplain evolution in a central European loess landscape – geoarchaeological investigations of the lower Pleiße valley in NW Saxony

Abstract. Undisturbed sediments are an important source for the reconstruction of the Holocene development of valleys. Wide floodplains with relatively small rivers in a region settled since 5500 BCE offer opportunities for investigations regarding climatic and anthropogenic landscape change. In the context of a motorway construction, excavations were carried out by the Saxonian Heritage Office in the year 2015. At one of the sites it was possible to get a view of the sediments of the Pleiße valley less than 100 m distance from large cross sections described by Neumeister (1964) in a former open cast mine. Archaeological finds and features, plant remains and radiocarbon dating as well as micromorphological and geochemical investigations helped to decipher the age and the characteristics of the Holocene sediments: above Weichselian loamy sands a sedge peat developed in small depressions during the Preboreal and Boreal. The sands and the sedge peat are covered by a “black clay”, which was still the topsoil during the Atlantic period. The sedimentation of 2.3 m thick overbank fines began after 4000 BCE. A depth of 1 m below the surface a medieval Slavic find layer was excavated. These results show that sedimentation processes in the lower Pleiße valley significantly changed after 4000 BCE. It is obvious that the increase in silty material in the floodplain is caused by the land clearance in the Neolithic period. More than half of the silty overbank fines were deposited before the Middle Ages began.