A sedimentological and isotopic study of the origin of supraglacial debris bands: Kongsfjorden, Svalbard

Debris bands associated with supraglacial moraines and associated basal deposits have been logged and sampled for their ice and debris at three glaciers in north-west Spitsbergen, Svalbard. Physical properties, including sediment concentrations, sediment particle-size distributions, clast macro-fabrics, and oxygen isotope compositions, indicate that all transverse and some longitudinal debris bands originate from the basal zone of these glaciers. Transverse supraglacial bands are composed of extensive stratified-facies basal ice that is enriched in 18O and which contains polymodal debris with spatially consistent clast fabrics. These properties suggest initial formation as basal ice and subsequent elevation into an englacial position by thrusting rather than formation as crevasse fills. The formation of longitudinal debris bands results from laterally compressive folding in response to the convergence of multiple flow units into a narrow glacier tongue. In common with transverse debris bands, longitudinal bands appear to be composed of stratified basal ice. The bands exposed at the surface of austre Brøggerbreen comprise two subfacies, strongly suggesting that the glacier was at least partially warm-based in the past, when the basal ice formed.