Redox Weathering of Ferruginised Regolith
The precursor for the ferruginous and ferro-manganiferous gravels in the Hanson Plain Sand is a ferricrete. In wet conditions the ferricrete undergoes fluctuating or seasonal reduction and oxidation. During reducing conditions, the Fe(III) becomes soluble as Fe(II) which can be mobilised and re-oxidised. The redoximorphic features of the regolith (mottling) are evidence of these conditions. The mottle patterns are quite wide ranging in variety and may be large blotches, almost regular rectangles (reticulate) or banded or laminar.
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These are three examples of mottle patterns in the weathered ferricrete. The Laminar, ‘Tiger Mottle” features are a special case. They do not occur everywhere but are extremely common south and south west of Colac. All of the mottling patterns result in fragmentation of the ferricrete and the isolation of residual hematitic gravels in the weathering mass. |
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