Abstracts of Symposium 55 and some papers from other related Symposia.

Late Quaternary Colluvium and Palaeosols in Kwazulu - Natal, South Africa: Evidence for Cyclical Accretion on Hillslopes

Greg BOTHA, Council for Geoscience, Geological Survey, P.O. Box 900, Pietermaritzburg, 3200, South Africa.

The most widespread Quaternary deposits in the hinterland of eastern South Africa are the colluvium and associated palaeosols which blanket many hillslopes, infill bedrock depressions and bury bedrock pediments. The recognition of a sequence of six pedoderms and several pedocomplexes has facilitated stratigraphic correlation of these deposits which are exposed in gullies over an area of 40 000 km in KwaZulu- Natal. Cross-cutting relationships between colluvial deposits and underlying palaeosols show that an alternation of gully cut-and-fill events and periods of pedogenic stability over the past 135 ka characterised the polycyclic accretion of colluvium. The periodicity of the seven recognised pedo-geomorphic cycles is defined by a framework of ¹⁴C and IRSL dates. Limiting dates for individual palaeosols provide a basis for evaluating the age of similar soils on the current landsurface.

Interpretation of palaeosol properties, palynological assemblages and isotopic data derived from palaeosol carbonates and organic matter, reveals changing palaeoenvironmental conditions since the "Last Interglacial" period, which was moister and slightly warmer than at present. Deeply weathered soils on upper hillslopes were eroded, and this rubified sediment re-deposited on colluvial footslopes, burying the gleyed and plinthic palaeosols formed during two hillslope cycles ca. 110 - 60 ka. Progressive environmental desiccation and cooling prior to, and during, the Late Pleistocene Hypothermal (ca. 40 - 14 ka), stimulated several hillslope cycles, represented by smectitic, vertic and sodic palaeosols and locally developed calcrete profiles. In some areas, increased colluviation buried alluvial terraces and apparently choked major rivers. Holocene hillslope processes are represented by localised colluvial deposits and calcrete nodule formation.

This colluvium/palaeosol succession has the potential for correlating similar deposits in the broader southern African region and to provide some continuity between isolated sites with high resolution palaeoenvironmental records.

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