Deep Regolith Weathering on the Summit Surface of the Southern Mount Lofty Ranges,South Australia: a Contribution to the ‘Laterite’ Debate

Chemical and mineralogical analyses of samples from a 102 m deep borehole and from road cuts on the summit surface of the Mount Lofty Ranges near Willunga Hill, are used to assess critically the view that the regolith here developed as a result of tropical, so‐called ‘lateritic’ weathering processes that developed a standard ‘laterite’ profile of great antiquity. There is no evidence of a former surface crust that comprises the upper part of a ‘standard laterite profile’. Moreover, there is no dramatic variation in chemical composition down the profile, with largely in situ localised weathering transformations explaining mineralogical variability. The presence of 2:1 layer silicates and the absence of gibbsite do not favour the operation of former intense tropical weathering, but the possible presence of chloritised smectite may have inhibited gibbsite formation. An iron‐depleted pallid zone does not occur at depth in the profile, but is present on the plateau margin. Many of the weathering features exposed in the road cuts can be explained in terms of modifications and developments under environmental conditions similar to those of the present, arguing against the view that the summit surface and its associated weathering mantle have been preserved in pristine form since the Mesozoic.