Methodology:

Quartz bearing erratic cobbles which showed evidence of transport by ice were collected at an exposed nunatak adjacent to Pope Glacier in the Amundsen Sea Embayment. Quartz mineral separation and Be-10 isotope dilution chemistry are largely based upon standard procedures (Kohl and Nishiizumi, 1992; Corbett, Bierman and Rood, 2016). The additional froth flotation step, used to separate feldspars from quartz was omitted as a precautionary measure (Nichols and Goehring, 2019). Once extracted from purified quartz, Be-10 AMS measurements were performed at the Australian Nuclear Science and Technology Organisation (ANSTO). Measurements were then normalized to the KN-5-3 standard with an assumed ratio of 6.320 x 10-12 (t1/2 = 1.36 Ma; Nishiizumi et al., 2007). Exposure ages were calculated via inputting Be-10 nuclide concentrations returned from AMS measurement using version 3 of the online calculators at hess.ess.washington.edu (Balco et al., 2008). The online calculators use the production rate scaling method for neutrons, protons and muons following Lifton et al., 2014 and summarised in Balco, 2017. Apparent exposure ages were reported assuming no erosion or snow cover and a material density of 2.7g cm-3

Data collection:

Sirius 6MV tandem accelerator (accelerated mass spectrometer)

Version 3 of online calculator at hess.ess.washington.edu (formerly known as CRONUS Online calculator).

Data quality:

Be-10/Be-9 measurements are normalized to the KN-5-3 standard with an assumed ratio of 6.320 x 10^-12 ( (t1/2=1.36 Ma, Nishiizumi et al., 2007)

Scoria cone (CIN) Be samples and process blanks BLK140920A/B were prepared for analysis at the CosmIC labs, Imperial College London. AMS analysis was performed at ANSTO, Australia