Field observations in conjunction with aerial images from an unmanned aerial vehicle were used to create the first map of a glacial unconformity underlying the late Carboniferous Dwyka Group of South Africa. Crosscutting relationships reveal that the glacial unconformity at Oorlogskloof, in which flutes, grooves, and striae were ploughed into unconsolidated sand, formed in a three-phased process charting a periodic shift in the locus of subglacial erosion. The unconformity formed by a periodically decoupled ice sheet in a probable tidewater setting. This model contrasts with earlier views that the structures simply record progressive ice-margin liftoff during transgression, and they provide unique insight into the complex temporal development of a 300 Ma subglacial environment.

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