GLACIAL EROSION OF HIGH-ELEVATION LOW-RELIEF SUMMITS ON PASSIVE CONTINENTAL MARGINS CONSTRAINED BY COSMOGENIC NUCLIDES

We present a new, extensive in-situ cosmogenic 10Be and 26Al dataset from high-elevation low-relief summits along Sognefjorden in Norway. Contrary to previous studies of high-elevation low-relief summits in cold regions, we find only limited cosmogenic nuclide inheritance in bedrock surfaces, indicating that warm-based ice eroded the summits during the last glacial period. From the isotope concentrations we model denudation histories using a recently developed Monte Carlo Markov Chain inversion model (Knudsen et al, 2015). The model relies on the benthic d18O curve (Lisiecki and Raymo, 2005) to discern between periods of exposure and glacial burial. The model results indicate substantial modification of the high-elevation low-relief surfaces through the Quaternary, which opposes the classical understanding of ice sheets as agents of selective erosion focused in valleys. Our results also have important implications for the understanding of high-elevation low-relief summits in general, as these have often been interpreted as relict landforms inherited from pre-Quaternary times and thus indicating long periods of surface stability. Our results point instead to substantial modification of these landforms by glacial and periglacial processes operating throughout the Quaternary.

References:

• Knudsen, M. F., et al. "A multi-nuclide approach to constrain landscape evolution and past erosion rates in previously glaciated terrains." Quaternary Geochronology 30 (2015): 100-113.
• Lisiecki, L. E., and Raymo, M. E. "A Pliocene‐Pleistocene stack of 57 globally distributed benthic δ18O records." Paleoceanography 20.1 (2005).