The Pleistocene of Schöningen, Germany: a complex tunnel valley fill revealed from 3D subsurface modelling and shear wave seismics

Abstract

The Pleistocene deposits of Schöningen represent an outstanding geological and archaeological archive, where an up to 45 m thick Middle to Late Pleistocene succession has been preserved and unique artefacts from the Lower Palaeolithic have been discovered. The preservation of such a thick and complete glacial/interglacial succession is very rare in the geological record and requires a specific depositional setting. We will present a new depositional model for the Pleistocene succession of Schöningen, integrating outcrop data, borehole data and high-resolution shear wave seismics. A total of four outcrop sections and 744 borehole logs were examined to document the complex facies architecture. All collected sedimentological and geophysical data sets were integrated into a high-resolution 3D geological model (GOCAD®) for reconstructing the spatial distribution of facies associations and the large-scale depositional architecture. The spatial distribution of the artefacts will be discussed with respect to the depositional environment.The Elsterian and Holsteinian deposits are restricted to a NNW–SSE trending, elongated trough, which is deeply incised into unconsolidated lignite-bearing Palaeogene deposits. The geometry of this erosional structure points to a tunnel valley origin that was incised below the Elsterian ice sheet. The basal tunnel valley fill consists of cross-stratified pebbly sand and gravel overlain by till. After deglaciation the tunnel valley remained underfilled and acted as a depocentre for interglacial deposition. During the subsequent Holsteinian interglacial (MIS 9) a lake formed within this depocentre and lacustrine sediments accumulated. This interglacial succession consists of peat, organic-rich silt and fine-grained sand interpreted as lake-bottom and deltaic sediments fed by surface run-off shed from the Elm ridge. The lacustrine deposition was controlled by repeated lake-level fluctuations in the range of 1–6 m leading to the formation of laterally stacked delta systems. These lake-level changes were probably triggered by climate, causing variations of precipitation and surface run-off. During the late Saalian glaciation the remnant tunnel valley was completely filled with meltwater deposits. The sedimentary facies and depositional architecture point to a shallow-water delta. Subsequently the meltwater deposits were overlain by till.The deposition of the Middle Pleistocene sediments within an Elsterian tunnel valley explains the unique preservation of the sedimentary succession of Schöningen. The long-lived interglacial lake provided an attractive site for animals and early humans ambushing them. Artefacts mainly became embedded on the delta plain, which rapidly was transgressed during lake-level rise and artefacts were thus preserved.