Gruppe für Paläo-Geoökologie

Soils and paleosols on the Swiss Plateau in the area of the former Rhone-Aare-glacier

Project leader: Heinz Veit

Co-workers: Christian Gnägi, Tobias Messmer, Mareike Trauerstein

Financed by: SNF 200021_149124/1

Duration: 2014-2016

It has been shown over the past few years that the glaciation and environmental history of the Alps is much more complex than previously assumed. While the dating of glacial sediments by luminescence has currently seen important improvement, it is still methodologically challenging. Another approach for constraining the age of glacial deposits is investigating their cover sediments and soils, because soil development (e.g. decalcification depth) and the complexity of cover bed sequences increases with the age of the underlying sediments. Additionally, investigating the cover beds, soils and palaeosols will not only provide indirect information on the time of glacial deposition, but also reflect the later environmental history of the region. Soil chronosequence studies in the alpine foreland have used geomorphological-stratigraphical models in the past, but lacking numerical dating control. Chronological constrains and environmental inter¬pre¬tations drawn from this approach are based on certain theoretical assumptions, such as: a) the glacier advance at about 25 ka ago was the most extensive one of the last glacial cycle, b) the Holocene was a period of land-scape stability, with closed vegetation cover and continuous soil development at least until the arrival of humans, c) periglacial surface features, such as solifluction layers, cryoturbations etc. are of Pleistocene age, because the formation of such features requires intense soil frost which is absent during the Holocene, and d) well-developed Bt-horizons reflect full interglacial environmental conditions (Holocene, Eem or older).
In this project we aim to challenge all these basic assumptions by combining intensive fieldwork with luminescence-¬dating. This is based on preliminary data we have obtained during the recent years, which contradict these “classical” views of the Upper Quaternary. Instead, our hypotheses are: a) the most extensive advance of the Rhone-Aare-glacier occurred prior to 25 ka, b) during the Early Holocene (ca. 10-8 ka) there was widespread erosion and sedimentation, indicating a relatively open landscape, c) frost dynamics with cryoturbation-like structures occurred at the same period (Early Holocene), probably due to pronounced seasonal contrasts (very cold winters, warm summers), and d) Bt-formation was possible during warmer periods of the Birrfeld glaciation and are not restricted to interglacials in a classical sense.
To prove these assumptions, we have to understand the spatial distribution of soils, their detailed structure, geochemical composition, and we need to know the age of the parent materials. Therefore, we aim at carrying out intensive fieldwork (studying gravel pits, hand- and motor corings, excavations), geochemical/mineralogical lab work, as well as luminescence and radiocarbon dating. The study will be realized in the area of the former Rhone-Aare-glacier glacier between Solothurn and Niederbipp, as well as the younger deposits in the lower Aare valley and the lake district (Lake Biel, Lake Neuchatel). This region features moraines and terraces of the supposed 25 ka advance, as well as deposits of older glaciations.