ICDP project DOVE: Drilling Overdeepened Alpine Valleys to decipher (a)synchroneities of glaciations around the Alps

The ICDP project DOVE (Drilling Overdeepened Alpine Valleys) Phase-1 investigates a series of drill cores from glacially overdeepened troughs at several locations along the northern front of the Alps. These basins provide an excellent but yet underexplored archive with regard to the age, extent, and nature of past glaciations. Drilling operations started in 2021 when two sites were drilled in the Northern Alpine foreland. In addition, DOVE analyses included four legacy sites providing a combined 1750 m of cored Quaternary sediment and over 40 m of underlying bedrock cores. A unified characterization of the sedimentary infill of these troughs allowed recognition of various orders of glacial sequences, which were defined by depositional pattern (lithology, sedimentology, geotechnics), wire-line logging data (petrophysics) and seismic data (seismic sequence stratigraphy and facies analysis). Several geochronological methods were employed and luminescence dating proved to allow assigning the glacial sequences to respective marine isotope stages (MIS).

This glacial sequence stratigraphy is interpreted in terms of glacial advance and retreat cycles into basins carved by this or by older glaciations. All drilled overdeepened glacial troughs contain more than one glacial advance-retreat leading to a stacked preserved record of past ice advances. Correlation of the glacial sequence stratigraphy across the northern Alpine arch emphasizes that most sediments were deposited during MIS 6, indicating a strong erosional and depositional pulse during the penultimate glaciation with two-to-three ice advances. Some troughs contain older sequences (i.e. MIS 8) indicating that MIS 6 might have reoccupied pre-existing basins formed by older glaciations. Erosion and infilling patterns during MIS 2 clearly contrast that from MIS 6 and older glacial cycles as many troughs remained underfilled since the Last Glaciation Maximum (LGM) and contain still lakes today. Moreover, it is important to note that during the last glacial cycle, a desynchrony of glaciations has been observed across the Alps, i.e. more extensive glaciation during MIS 4 as well as an earlier onset of the last glacial advance in the western Alps. This can be explained by shifts of the polar front over the North Atlantic that caused different regional maxima of precipitation, which triggered spatial offsets in the timing of past glaciations.

Overall, the overarching pattern emerging from DOVE Phase-1 so far is the dominance of MIS 6-dated sedimentary fills of overdeepenings with older sequences only preserved in a few selected sites. MIS 6 played obviously a key role in landscape evolution along the northern margin of the Alps. This consistent pattern is very surprising and poses the question if it also occurs around the entire Alpine arch, or whether it is restricted to the northern Alpine sections that were covered in DOVE Phase-1. Thus, a prolongation within DOVE Phase-2 is currently planned to comprise four sites in overdeepened troughs in the southern and western areas (Slovenia, Italy, France).