Unravelling the changing depositional history of sediments preserved in glacially overdeepened alpine basins, by establishing the geochronology of five drill cores using luminescence dating

SUPERVISOR: Markus FIEBIG

PROJECT ASSIGNED TO: Gustav FIRLA

Areas affected by former glaciations can be identified by remnants left in the environment. Evidence of former glaciers can not only be traced by the geomorphological record preserved at the landscape surface (e.g. moraines, drumlins, erratic blocks), but can as well be available underground and protected from post depositional alteration of sedimentary structures. Glacially overdeepened basins are subterranean structures incised into the underlying bedrock by glaciers and filled with eroded material from the adjacent landscape. Glacially overdeepened basins can be viewed as the complementary part to the alpine slopes with regards to source-sink models. The fill of overdeepened structures potentially stores vast amounts of sediment and can therefore serve as a sedimentary archive. They reflect and preserve depositional processes. In addition, they indirectly allow for the reconstruction of environmental conditions and mass movement events. The morphology of overdeepenings is influenced by internal and external mass movements. Sedimentary structures reflect the changing relief of the overdeepened basin and therefore the mass movement history.

Past climate change affected the extent of glaciers significantly. The sediment infill of overdeepened valleys is representative of glacial fluctuations. Identifying deposits of different glacial cycles is crucial to understanding how glaciations affected the landscape of the Northern Alpine Foreland.  

My research is part of the multinational pan-alpine ICDP - DOVE (International Continental Scientific Drilling Program - Drilling Overdeepened Alpine Valleys) project. Contributors from different universities, government agencies, and other institutions set out to answer the following research questions:

• What can we learn about past glaciations from the sediment fill of overdeepened valleys?
• How are overdeepenings formed?
• What can the provenance of the basin material tell us about past sediments paths and therefore the past surrounding geomorphology?
• Are mass movement events preserved in overdeepened basins?

Five overdeepenings around the northern Alps will be investigated by DOVE team members. Drill-cores in each overdeepened through will help us answer the before mentioned research questions. In addition to the pinpoint information gathered by sedimentological analysis of the drill cores, geophysical data will widen our view of the investigated overdeepened valleys.

My contribution to the ICDP - DOVE research project is the sedimentological analysis of the Schäftlarn (south of Munich, Germany, ICDP-5068_3) and Neusillersdorf (west of Freilassing, Germany, ICDP-5068_4) drill-cores and constraining the age of the ICDP - DOVE drill-cores using luminescence dating techniques. These methods are used to derive the time that has passed since the last sunlight exposure of the analysed sediment. With well-established and cutting-edge luminescence dating techniques we will establish when the sediment deposition into the overdeepened basins started, ended, at which rate sedimentation occurred and if gaps in the sedimentation history are present (i.e. periods of intensified erosion or absence of sediment influx). With the added temporal perspective of the DOVE drill-cores we will be able to quantify sedimentation, erosion and the long-term history of mass movement events in the investigated overdeepened structures.

^{Fig. 1: The basic principle of luminescence dating.}

^{Fig. 2: Exemplary scan of the Schäftlarn drill-core (ICDP 5068_3) at 115,5 m.}