Abstract

During the Late-Ordovician glacial period, the upper ~50 m of the quartz arenite Peninsula Formation (Table Mountain Group) was subject to a large-scale, soft-sediment deformation event, forming ellipsoidal synforms with wavelengths of up to 150 m. The de Balie locality in the Western Province, South Africa, provides clear 3D exposures into the morphology of these folds. Comparisons with experimental soft-sediment deformation and modern observations of periglacial environments suggest a single deformation event during which large-scale fluidization and gravitational instabilities (load casts) were triggered by thermal destabilisation. The fold morphology is inconsistent with previous interpretations that the folds were formed by ice contact shearing.

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