Late Quaternary glaciation in the Hebrides sector of the continental shelf: cosmogenic nuclide dating of glacial events on the St Kilda archipelago

St Kilda archipelago, located ~65 km west of the Outer Hebrides and ~60 km east of the Atlantic shelf break, provides critical evidence that challenges the assertion that the British–Irish Ice Sheet (BIIS) extended to near the shelf edge during the Last Local Glacial Maximum (LLGM; c. 27 ka). Cosmogenic nuclide dating of perched boulders at 290 m altitude on the largest island, Hirta, yields consistent exposure ages averaging ≥81.6±7.8 ka, demonstrating that the last ice sheet did not overrun high ground. Additional dating of glacially emplaced boulders on low ground indicates small, locally nourished glaciers occupied a north-facing valley (Gleann Mòr) at c. 30.9±3.2 ka and a south-facing valley (Village Bay) at c. 19.2±2.3 ka. These findings contradict the traditional view of ice sheet behavior during the LLGM, suggesting either surge-like transient streaming behavior or an earlier, more extensive ice sheet. The final glaciation of Village Bay occurred out of phase with the BIIS's overall retreat.

Ballantyne, C. K., Fabel, D., Gheorghiu, D., Rodés, Á., Shanks, R., & Xu, S. (2017). Late Quaternary glaciation in the Hebrides sector of the continental shelf: cosmogenic nuclide dating of glacial events on the St Kilda archipelago. Boreas, 46(4), 605–621. Portico. https://doi.org/10.1111/bor.12242