Ein neues EEM-zeitliches Umweltarchiv am Spiezberg (Schweizer Alpen) im Kontext der mittel- und spätpleistozänen Landschaftsentwicklung

Zwahlen, Peter; Tinner, Willy; Vescovi, Elisa (2021). Ein neues EEM-zeitliches Umweltarchiv am Spiezberg (Schweizer Alpen) im Kontext der mittel- und spätpleistozänen Landschaftsentwicklung. In: Thalmann, Christoph (ed.) Zeitreisen II. Mitteilungen der Naturforschenden Gesellschaft in Bern: Vol. 78 (pp. 92-121). Bern: Naturforschende Gesellschaft Bern

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Map and profile constructions in the region Lake Thun (Bernese Oberland, Switzerland) lead to speculations of different glacial erosions (extensive gravel during glacial advance, dynamic erosion during ablation) in early studies. Historically explanatory models operating with several ice ages are proven back to the 19th century. At the beginning of the baroque 18th century, Johann Jakob Scheuchzer mislead himself to «diluvial» speculations based on his precise observations about «schist coals» covered by gravel layers studied during the construction work for the Kander river deviation.
This «shist coals» consist of organic sediments from lakes and mires and were attributed to Quaternary interglacials or interstadials during the 20th century. In 2005, at Spiezberg, above the left shoreline of Lake Thun, an exploration drilling was conducted for an excavation pit. As a result, 7 m thick intermoraine still water sediments (laminated silt and clay with gyttja and fossil wood residues) were unexpectedly found. This sediment profile has been ideally suited for stratigraphical studies. The presented analyses (sedimentology, palynology, radiocarbon dating, paleogeography) lead to the following results: The lake or pond sediments, respectively, are interglacial deposits, which, geo- and biostratigraphically, we assign to the Eemian interglacial. These still water deposits are intercalated between coarse river deposits and glacial till. Paleogeographical correlations with pre-identified sediments from the middle to upper Pleistocene of the region Lake Thun – Aare Valley allow a spatial reconstruction of the Eemian-water bodies and the following early Würm glacial advance gravels.

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