Lateglacial to Late Holocene landscape history derived from floodplain sediments in context to prehistoric settlement sites of the southern foreland of the Harz Mountains, Germany

The Harz Mountains are Germany's northernmost low mountain range. The southern foreland is characterised by a fragmentary distribution of loess and loess-like deposits. During prehistoric times this region was sparsely populated, in contrast to the adjoining southern floodplain of the Helme River, which has been a favoured settlement area since the Neolithic period. This study focusses on the onset of human impact on the landscape and aims to reconstruct the landscape development of this peripheral prehistoric settlement area under a long term perspective (Lateglacial to Late Holocene). The study is based on the sedimentological analysis of six sediment profiles from the floodplain of two small valleys. The chronology of the sedimentological records is provided by 24 new AMS radiocarbon ages that range from 21.7 ka BP to 0.1 ka BP. Three major changes in the depositional environment are observed in the sediment records representing the landscape evolution: a) During the Lateglacial, periglacial conditions prevailed and deposition and reworking of loess occurred on the slopes, while in the floodplains periglacial cover beds and alternating partly gravelly layers of silts and clays were deposited. b) From Preboreal to Atlantic periods a marked rise in the groundwater table led to authigenic precipitation of carbonates in the floodplains under ameliorated climatic conditions. During this phase the valleys were progressively filled by intercalated organogenic and calcareous sediments. c) Human influence on the landscape is reflected in colluvial and alluvial deposits indicating the occurrence of human-induced soil erosion and is dated prior to the beginning of the Bronze Age (here corresponding to Subboreal period). During the period of the Little Ice Age gully incision occurred, probably as a result of an intensified land use in upslope areas and of high-magnitude precipitation events during this period.