Greg Botha

Colluvial deposits provide an interesting challenge for luminescence-dating techniques because of the short and varied light-exposure histories of the grains prior to deposition. Results of thermoluminescence (TL) and infrared stimulated luminescence (IRSL) measurements are presented for two stacked colluvial deposits from Natal. A radiocarbon date for bulk organic matter in the A horizon of the soil formed within the surface of the lower unit provides a means of assessing the suitability of various luminescence procedures for such material. The overlying colluvium contains grains bleached to varying extents, as shown by the range of EDs for the coarse-grain feldspar separate obtained using the single-aliquot IRSL method. For this sample all age estimates (either by IRSL or TL) are too large compared with the radiocarbon age, indicating that even the IRSL signal was not zeroed in all grains before they were buried. The underlying colluvium contains grains bleached more uniformly, resulting in a smaller range in the values of single-aliquot EDs; the agreement of the IRSL age with the radiocarbon age indicates that the IRSL signals of all grains were zeroed prior to deposition. The TL results for this sample suggest that the signals were not totally zeroed, but had experienced considerably more light at deposition than the grains from the overlying unit.

The Cenozoic stratigraphy of South Africa has developed over the past 166 years since geological mapping of the region was initiated. The current status of lithostratigraphy and the global chronostratigraphic framework is discussed in the context of the diverse Cenozoic regolith across the region. Geological mapping here utilizes lithostratigraphy to organise the Cenozoic deposits, although some extensive units are characterised informally using lithological descriptors. Although there are no formal biostratigraphic units, the allied use of “Land Mammal Ages” compiled from fossil type sites is described. An analogous archaeological cultural-historical “technocomplex” stratigraphy is outlined to subdivide stone age cultural material commonly associated with Quaternary deposits and has often been used as a relative dating framework. A summary table of Cenozoic regolith is presented, differentiating deposits into their terrain morphologically defined Geomorphic Province context as a me...

Detailed 1:10,000 scale engineering geological mapping of Pietermaritzburg covered an area of approximately 670km 2 , some of which is experiencing rapid growth and development across a geologically varied area. This variation has resulted in a number of differing geological and geotechnical conditions, some of which are problematic and likely to have significant negative consequences for future developments. The mapping provided very detailed engineering geological coverage of the area and focused on delineating areas where hazardous geological or geomorphological conditions could impose environmental constraints or elevated cost implications on future infrastructure development. The use of digital elevation data has enabled the production of innovative map products that provide enhanced visualisation of the geotechnical and engineering geological data for the area. The geological and terrain morphological diversity of the Pietermaritzburg city bowl and surrounding hilly areas resu...

Abstract A detailed field survey identified a late Neogene sedimentary succession which accumulated in ephemeral palaeolakes on the edge of the Kalahari Basin in the northwest of Transvaal Province, South Africa. Palygorskite and dolomite formed along lake margins which fluctuated between lacustrine and dry-land conditions. The sedimentary sequence presented an opportunity to investigate the interrelationships between these minerals and study their possible modes of formation, either by lacustrine sedimentation or pedogenic processes. Clay mineralogy, transmission and scanning electron microscopy and geochemical analysis revealed an increase in magnesium-enriched minerals, palygorskite and dolomite, within the pedogenically altered marginal lacustrine sediments. Field relationships showed that the dolomite is a replacive phase within the decomposing palygorskite, although the scanning electron micrographs do not display such unequivocal evidence for a direct replacive relationship. They suggest rather that the dolomite forms by neoformation from soil solutions, which included decomposition products released by the breakdown of the palygorskite. Seen in a regional context, subaerial pedogenic processes acted on marginal lacustrine sediments and resulted in the decomposition of smectite and neoformation of palygorskite. A change in climate to drier conditions encouraged the formation of calcrete in surrounding areas which increased the magnesium/calcium ratio in groundwaters. This increase was supplemented by evaporative concentration during the desiccation of the lacustrine environment. The high magnesium concentration led to the formation of the dolomite-rich dolocrete. This interpretive model is a means by which existing genetic models for calcareous pedocretes and those models that define the concentration of magnesium in groundwater and saline lacustrine environments can be combined. The pedogenic mineral relationships described are suggested as useful palaeoenvironmental indicators for the late Neogene/early Pleistocene of southern Africa.

The layer of soil - the Earth's 'living skin' - is thinner than we think. That extraordinary ratio 1:12 700 represents its thickness in comparison to that of the rocks beneath. By way of illustration, the layer of paint on the outside of a house, relative to the size of the house, is ten times thicker!

Soil erosion is one of the most challenging environmental issues in the world, causing unsustainable soil loss every year. In South Africa, several episodes of gully erosion have been documented and clearly linked to the presence of Quaternary colluvial deposits on the Drakensberg Mountain footslopes. The aim of this study was to identify and assess the triggering factors of gully erosion in the upper Mkhomazi River basin in KwaZulu-Natal, South Africa. We compiled a gully inventory map and applied remote sensing techniques as well as field surveys to validate the gully inventory. The gullies were subdivided into slope gullies and fluvial gullies. We derived susceptibility maps based on the spatial distribution of gully types to assess the most important driving factors. A stochastic modeling approach (MaxEnt) was applied, and the results showed two susceptibility maps within the spatial distribution of the gully erosion probability. To validate the MaxEnt model results, a subset of...

ABSTRACT The devastating impact of landslides and secondary instability with their unconsolidated depris deposits due to weathering, settlement and groudwater seepage are significant geological threats. Mass movemets can impact negatively on urbanisation and represent a critical factor determining landuse zonation during town and regional planning. Mapping and classification of mass movement deposits in the KwaZulu-Natal Province highlighted the more widespread extent of there Quaternary geomorphic desepquilibrium indicators than is commonly appreciated. Many of the largest occurrences mapped are palaeo-landslides located in areas of high rlief and steep slopes in the Ukhahlamba-Drakensberg footlopes and the major fiver valley. Some of these events temporatily blocked river channels resulting in changed channel and floodplain morphology. However, the majority of the landslides identified are smaller, more, recent, localized occurrences associated with high intensity rainfall events. Accelerator Mass Spectormetry (AMS) or radiocarbon dating of bulk organic material derived from ponds on back-tilted surfaces (sag ponds) of the palaeo-landslides has yielded minimum ages for the landslide events.

Evidence of Late Pleistocene and Holocene palaeoenvironmental change in the northern hinterland of the KwaZulu-Natal province, eastern South Africa, is preserved within a widespread sequence of colluvium and intercalated palaeosols, comprising the Masotcheni Formation. Palaeosol profile characteristics and micromorphological features are described for the full stratigraphic succession, preserved at the St Paul's donga reference site and other comparative exposures, permitting

... The escalation of agricultural, pastoral and Iron Age industrial practices during the past 1000 years probably accelerated donga erosion ... Another possible explanation for the age discrepancy is that the Hazeldene Pedoderm radiocarbon date at Nqutu is correct ... Ph.D. thesis, Univ ...

The post-Karoo age sedimentary succession known formerly as the Malvernia Formation, is currently termed the Malonga Formation, ‘Formaçao de Sena’, ‘Formaçao de Singuédeze/Elefantes’ and Gona-re-Zhou Plateau Beds in the Limpopo Basin region where South Africa, Mozambique and Zimbabwe have common borders. These rocks represent continental, taphrogenic sedimentation on the eastern margin of the emergent African continent after the breakup of

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