Erosion-surfaces, tectonics and volcanic activity in Uganda

Abstract

The historical development of the erosion-surface nomenclature previously used in Uganda is reviewed briefly. Several surfaces are defined, or re-defined, and together with their component physiographic units are described and given local names referring to areas in eastern and central Uganda. For eastern Uganda the sub-volcanic (broadly early Miocene) topography is reconstructed in detail and its subsequent modification is described. In central Uganda two major erosion-surfaces are recognized. Post-formational amendments to these former landscapes are discussed in relation to the present drainage-pattern and to tectonic deformation associated with the development of the Lake Albert-Edward graben. The stratigraphical-geomorphological history of the Western Rift south of the Murchison Falls is summarized. Sequences of events in the formation of the present landscape are outlined for eastern, central and western Uganda, and extrapolation is made from the eastern region into adjacent areas of Kenya. Some recasting of established sequences is suggested. It is concluded that insufficient attention has been paid previously to the local physiographic setting (often dominated by the form of the sub-volcanic landscape) controlling the stratigraphical relations and lithology of the fossiliferous Miocene volcanic and other sediments. The extent of late Tertiary and Quaternary tectonic deformation of erosion-surfaces has in the past been underestimated.