Origin and timing of erratic boulders on Disko Island, Greenland

Glaciers and ice sheets are observed to rapidly change under the current global climate conditions. In Europe this is particular the case for Greenland. Yet, for future projection it is of key importance to provide a long-term, multi millennial perspective on changes of Greenland outlet glaciers and local glaciers. For example, the dating of glacial deposits (e.g. moraines, rock boulders etc.) provide an essential time component to the understanding of glacial retreat.

The project "Origin and timing of erratic boulders on Disko Island, Greenland", funded by the Swiss Polar Institute (SPI), focuses on glacial erratics, thus deposited allochthonous material that differs from the rock type of its current resting area on Disko Island in Western Greenland. Here, granitic boulders (Orthogneiss) of the Precambrian basement rest on the Palaogene island basalt. The goal is to identify the time of deposition and the source of these erratic boulders.

The goal is to identify the time of deposition and the source of these erratic boulders. With the use of cosmogenic radionuclides (e.g. ¹⁰Be), surface exposure ages of these granitic glacial erratic boulder will be determined at two different island positions. the southerns slope on Disko Island will provide important constraints in the thinning and timing of deglaciation of the former ice stream covering Disko Bugt. It will further provide a minimum age constraint for the rock glaciers that are researched by the 3G group of the University of Zurich. The additional mapping and dating of erratic boulder on the ~800 m a.s.l. high basaltic plateau will provide new constrains on ice cap and ice sheet thickness during the last and potentially previous ice age glaciations. It is currently not known, if the ice sheet has overflown this mountainous plateau in the last ice age or at which previous ice age, and hence dating will provide former ice sheet thickness constraints. The origin of the glacial deposits will be traced back by comparing the petrography and chemical signature (e.g. XRF analysis) of the erratic boulder with the various Precambrian rocks (e.g. diorite, tonalite, etc.) of Western Greenland. The identification of the erratic rock source(s) helps the modelling of the material transport and ice flow direction.