Chapter 5: Evidence for Periglacial Processes and Environments in the Port Askaig Formation

The Port Askaig Formation (PAF) includes a variety of features that have been interpreted as periglacial in origin. This chapter systematically analyses previously published data and offers new insights concerning cold-region processes based on further observations of the PAF undertaken between 2012 and 2025. Features include: (1) sandstone wedges interpreted primarily as infilled thermal contraction cracks and, in a few cases, as subglacially formed hydrofractures; (2) “downfolds” of sand and gravel, which are typical of periglacial involutions and patterned ground; (3) angular clasts, commonly in isolated clusters, which occur on diamictite beds penetrated by sandstone wedges, and are the product of frost action on subaerial till surfaces; (4) sheet-like spreads of angular breccia which are the product of down-slope movement of frost-shattered regolith (“gelifluctite”); (5) angular sandstone intraclasts within conglomerates, which are the product of the collapse of frozen sandy river banks; and (6) diamictites with structural attributes that are indicative of glacier-permafrost interactions. The combination of these features in multiple locations enables the identification of five principal periglacial horizons. The environment at the time these features were formed was a till plain with local palaeoslopes, periodically disturbed by glaciotectonic processes, resulting in complex facies associations and distinctive landforms.