POSTPALEOZOIC EVOLUTION OF WEATHERED LANDSURFACES IN UGANDA BY TECTONICALLY CONTROLLED DEEP WEATHERING AND STRIPPING

A model for the evolution of weathered landsurfaces in Uganda is devel oped using available geotectonic, climatic, sedimentological and chron ological data. The model demonstrates the pivotal role of tectonic upl ift in inducing cycles of stripping, and tectonic quiescence for cycle s of deep weathering. It is able to account for the development of key landforms, such as inselbergs and duricrust-capped plateaux, which pr evious hypotheses of landscape evolution that are based on climatic or eustatic controls are unable to explain. Development of the Ugandan l andscape is traced back to the Permian. Following late Palaeozoic glac iation, a trend towards warmer and more humid climates through the Mes ozoic enabled deep weathering of the Jurassic/mid-Cretaceous surface i n Uganda during a period of prolonged tectonic quiescence. Uplift asso ciated with the opening South Atlantic Ocean terminated this cycle and instigated a cycle of stripping between the mid-Cretaceous and early Miocene. Deep weathering on the succeeding Miocene to recent (African) surface has occurred from Miocene to present but has been interrupted in the areas adjacent to the western rift where development of a new drainage base level has prompted cycles of stripping in the Miocene an d Pleistocene. (C) 1998 Elsevier Science B.V. All rights reserved.