Importance of sampling across an assemblage of glacial landforms for interpreting cosmogenic ages of deglaciation

Abstract

Deglaciation chronologies for some sectors of former ice sheets are relatively poorly constrained because of the paucity of features or materials traditionally used to constrain the timing of deglaciation. In areas without good deglaciation varve chronologies and/or without widespread occurrence of material that indicates the start of earliest organic radiocarbon accumulations suitable for radiocarbon dating, typically only general patterns and chronologies of deglaciation have been deduced. However, mid-latitude ice sheets that had warm-based conditions close to their margins often produced distinctive deglaciation landform assemblages, including eskers, deltas, meltwater channels and aligned lineation systems. Because these features were formed or significantly altered during the last glaciation, boulder or bedrock samples from them have the potential to yield reliable deglaciation ages using terrestrial cosmogenic nuclides (TCN) for exposure age dating. Here we present the results of a methodological study designed to examine the consistency of TCN-based deglaciation ages from a range of deglaciation landforms at a site in northern Norway. The strong coherence between exposure ages across several landforms indicates great potential for using TCN techniques on features such as eskers, deltas and meltwater channels to enhance the temporal resolution of ice-sheet deglaciation chronologies over a range of spatial scales.

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…Rinterknecht et al, 2006;Balco and Schaefer, 2006;Stroeven et al, 2010Stroeven et al, , 2011, but dating of more extensive pre-LGM glaciations has been applied to the north-eastern FIS (Linge et al, 2006), the northern Cordilleran Ice Sheet (Ward et al, 2007;Stroeven et al, 2014) and the Patagonia Ice Sheet (Kaplan et al, 2007;Darvill et al, in press). …”

Ice sheet sources of sea level rise and freshwater discharge during the last deglaciation

“…The existing SIS chronology for the Holocene is based largely on the varve records from Sweden and Finland from the Baltic Sea/Ice Lake [ Cato , 1985; Fromm , 1985], several minimum‐limiting radiocarbon dates on bulk organic matter and macrofossils from northern Sweden [ Andersen , 1981; Karlen , 1979], and cosmogenic radionuclide dates from northern Sweden [ Stroeven et al , 2011]. The oldest macrofossil radiocarbon date on wood from northern Sweden places deglaciation of this region ice‐free before 9.5 ± 0.2 ka (8.48 ± 0.16 14 C ka BP, ST‐4507) [ Karlen , 1979].…”

Surface exposure dating (36Cl and 10Be) of post‐Last Glacial Maximum valley moraines, Lake District, northwest England: some issues and implications

“…Two to three metres of rock thickness is often considered to be sufficient for this (e.g. Balco, ; Stroeven et al ., ), although Braucher et al . () reported measurable concentrations of 36 Cl, 10 Be and 26 Al at depths of up to 11 m below the surface.…”

“…Two to three metres of rock thickness is often considered to be sufficient for this (e.g. Balco, 2011;Stroeven et al, 2011), although Braucher et al (2011 reported measurable concentrations of 36 Cl, 10 Be and 26 Al at depths of up to 11 m below the surface. Where insufficient rock thickness is removed, by glacial erosion for example, the resulting bedrock surface will retain isotopes acquired during the pre-glacial phase of subaerial exposure and when analysed will yield anomalously 'old' exposure ages.…”