Morris Viljoen

A Reappraisal of Some Aspects of Precambrian Shield Geology

Attention is drawn to some of the misconceptions regarding the ancient crystalline shields, and an attempt is made to clarify some of the ideas held on their geology. In Southern Africa, the Precambrian shield is well represented and exposed, and recent studies of it reveal a clear and well-defined pattern of events in its evolution. The very ancient, stable, cratonic nuclei incorporating the greenstone belts are termed “The Earliest Precambrian.” Traversing the shield areas and surrounding the cratonic nuclei are large, elongated, highly metamorphosed and granitized “Precambrian Mobile Belts.” Although younger than, and totally different in character to, the cratons which they tend to encircle, they nevertheless form an integral part of the crystalline shields. The fundamental elements of the geology of the greenstone belts within the cratonic nuclei, together with a distinctive pattern of relationships between the greenstone belts and their surrounding granitic terrain are repeated with remarkable consistency in other shield areas of the world, especially in Canada and Western Australia. The geological features which typify and contribute to the establishment of this highly distinctive pattern are outlined in the text and demonstrated with the aid of tables and diagrams. The world-wide uniformity of the stratigraphy, structure, metamorphism, mineralization, associated granites, and geotectonic setting of the greenstone belts is stressed. An attempt is made to reconstruct an evolutionary model of the development of the early Precambrian granite-greenstone belt terrain. This avoids direct comparisons with younger geological features and events, particularly the younger, Alpine-type orogenic belts with which early Precambrian geology has frequently been compared and equated. The mobile belts are briefly discussed, and again it is suggested that their evolution was not necessarily along the lines suggested for Alpine orogenesis.

The Kruger National Park: Geology and Geomorphology of the Wilderness

The Kruger National Park is an outstanding wildlife site and ecological resource where ecosystems and their functions are strongly influenced by underlying geology, geomorphology, soils, climate and water resources. This chapter outlines the general geology and geomorphology of the Kruger area. Landscape evolution and landform development during the Cenozoic has also been strongly controlled by the varied geological formations present in Kruger. Landscape development has included the exposure of bedrock surfaces by uplift and erosion, the accumulation of weathered products to form soil s and the subsequent transportation of alluvial sediments within the riparian zone of Kruger’s rivers. The interrelationships between these factors and their role in ecosystem development and cultural landscape features are examined.

The Mpumalanga/Limpopo Escarpment: Geology and Fluvial Landforms

The Mpumalanga/Limpopo sector of the Great Escarpment of northeast South Africa is unique in its wide variety of rock types which have largely controlled the formation and morphology of the spectacular landscapes of the region. This chapter describes how epeirogenic uplift of the escarpment, followed by headward erosion by rivers into different geological formations, has sculpted different landforms and largely controlled the development of features such as waterfalls, scarp faces, gorges and canyons. Pothole formation in harder rocks has been a major factor in the development of gorges . The weathering characteristics of dolomite formations and nature and origin of dolomitic caves , their dripstone deposits and calcareous tufa deposits along the escarpment region are also described. The spectacular natural features of the region have made it a popular tourist destination.

Tertiary education requirements in the geosciences for the minerals industry and in the environmental field to meet the demands of the 21st century in South Africa

Abstract South and southern Africa are currently facing a major skills shortage in the applied earth sciences, particularly in the minerals industry and in the environmental field. This paper offers outlines of course curricula, developed in South Africa, which are designed to meet these needs. It is argued that insufficient time is devoted to applied geology in degree courses in South Africa and that appropriate specialisations should be introduced into the third and fourth years of Earth Science degrees. More detailed specialisation should be offered at masters level. Examples of such courses currently run in South Africa are cited. The important contribution of the earth sciences to contemporary environmental issues is stressed and the need for environmental geologists emphasised. It is argued that the huge amount of information essential to environmental geology requires postgraduate level teaching of this subject. An example of such a masters level course is taken from a course planned at the University of the Witwatersrand. Courses similar to those being developed in southern Africa need to be developed in other African regions.