Aquatic and terrestrial proxy evidence for Middle Pleistocene palaeolake and lake‐shore development at two Lower Palaeolithic sites of Schöningen, Germany

Abstract

The archaeological sites in the open-cast mine of Schöningen, Germany, represent outstanding archives for understanding Middle Pleistocene interglacial-glacial transitions and human adaption. Aquatic microfossil and pollen assemblages from the 'Reinsdorf sequence', likely correlated to Marine Isotope Stage 9, document environmental changes from a thermal maximum to succeeding glacial conditions recorded in two sequences of excavation sites 12 II and 13 II. Multi-proxy analyses enable detailed reconstruction of lake-shore and landscape developments despite variable microfossil preservation in changing carbonate-and organic-rich deposits. Rich aquatic vegetation with abundant charophytes suggests repeated phases with water depths of 0.5-2 m at site 13 II, while even greater temporary depths are deduced for 12 II DB. Mesorheophilic and mesotitanophilic ostracod species indicate stream inflows with medium-low calcium contents of >18 mg Ca L -1 originating from nearby springs. Diatoms point to meso-eutrophic conditions and an alkaline pH of the lake water. Interglacial conditions with thermophile forests but no aquatic microfossils preserved, suggesting a dry or only temporarily flooded site, mark the beginning of the sequence. Continuous presence of aquatic organisms and overall dominance of small tychoplanktonic diatoms during a subsequent cool steppe phase provide evidence for increasedwater depths and unstable habitats characterized by erosion and probably prolonged periods of lake ice cover. During the succeeding boreal forest-steppe phase, surface runoff into the productive, shallow lake decreased due to a more extensive vegetation cover. Concurrently, intensified groundwater input in contact with the nearby salt wall caused elevated salinities. Following a lake level drop, stream inflows and lake levels increased again towards the end of the Reinsdorf sequence and promoted development of a diverse fauna and flora at the lake shore; thereby maintaining an attractive living and hunting environment for early humans during a phase of generally cooler temperatures and landscape instability at the transition into a glacial period.

Landscape dynamics and chronological refinement of the Middle Pleistocene Reinsdorf Sequence of Schöningen, NW Germany

“…Charophyte species assemblages and developments closely mirror each other in the two sequences (Supplemental Table 3; Krahn et al, 2021), thereby validating and complementing each other. Some (sub-)sublevels are better defined or newly analyzed in sequence PRP 13 II (2014) and ZB 13 (2018) because of the higher number of samples and longer, well-developed sequence.…”

“…Lake level rose distinctly during that time interval, which is assumed to have contributed to lake-bottom anoxia in addition to the deposition of coarse-grained sediments and an assumed higher sediment accumulation rate (Sigg and Stumm, 2011;Kasper et al, 2013). Increased abundances of mesorheophilic ostracodes indicate flowing waters and a phase of increased surface-stream inflows, which was ascribed by Krahn et al (2021) to reduced vegetation cover in the catchment. Biogenic productivity during sedimentation of level II-2c1 tends to increase slightly with slightly higher C/N ratios, and thus elevated amounts of terrestrial biomass (Meyers, 2003).…”

Spatial interpretation of high‐resolution environmental proxy data of the Middle Pleistocene Palaeolithic faunal kill site Schöningen 13 II‐4, Germany

“…This suggests a water depth of around 0.5–2 m for sublevel 13 II‐4c of the Reference Profile based on its charophyte assemblage (Krahn et al . 2021). Furthermore, the authors proposed that a period of cooler climates with reduced vegetation cover led to increased surface stream inflow fed by small springs from the nearby mountain range Elm.…”

“…High abundances of tychoplanktic diatoms such as the small fragilarioid species occurring at Schöningen site 13 II (Krahn et al . 2021) were related to erosion (Hickman & Reasoner 1994, 1998), environmental instability (Denys 1990) and longer periods of ice‐cover on the lake (Lotter & Bigler 2000). Increased fluvial activity is detected close to the position of ID 9863 by the highest proportions of small tychoplanktic diatoms of all samples and markedly increased abundances of I. bradyi and P. zenkeri , ostracod species which prefer flowing waters or even avoid standing waters (Meisch 2000).…”

“…At the archaeological find complex 13 II five lithologically clearly distinguishable units, 13 II‐1 to 13 II‐5, were defined at the Reference Profile (RP) of 2003 (Thieme 2007a, b) reflecting lake‐level fluctuations resulting from climate and vegetation changes (Urban & Bigga 2015; Krahn et al . 2021; Tucci et al . 2021).…”