REPLY TO THE DISCUSSION BY C.D. ROWE AND N.R. BACKEBERG ON THE PAPER “RECONSTRUCTION OF THE ORDOVICIAN PAKHUIS ICE SHEET, SOUTH AFRICA” BY H.J. BLIGNAULT AND J.N. THERON (SAJG,113, 335–360, 2010)

Rowe and Backeberg (this volume) compares the morphology of cm scale structures formed by fluidization with similar looking structures of the Fold Zone (tens of m scale) for which Blignault and Theron (2010) proposed a model of folding essentially by buckling. The Blignault and Theron model is an integration of structure, glaciological aspects and lithofacies associations as observed over the full outcrop area of ca 300 km. Some of the comments made by Rowe and Backeberg require clarification. They are of the opinion that folding by buckling results in “an essentially unlimited long axis”. However, the extent of fold axes is a function of the extent of the stress field causing the folding. Blignault and Theron (2010) noted that research published during the last ten years on the ice-bed interface, shows how ‘sticky spots” vary spatially and temporally as water pressure at the interface varies. The implication is …