Relation Ship Sbetween Geology, Mor Phology and Soil Associations of Bichena Area ( S. E. GOJAM )

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Addis Ababa Universty


The study investigates the extent of influence of the geolog- ical history , essentially parent rock * topography and time , on soil formation and distribution in Bichena , Southeastern Gojjam * Lithostratigraphy of the Mesozoic sedimentary sequence and Cenozoic volcanics is described * An attempt has been made to reconstruct the morphologic evolution of the area * Four soil mapping units in close relationship with the parent material and geomorphology have been differentiated: Vertisol, Mollisol, Alfisol and Entisol Orders 0 The soils are found to assume different states when the above considered soil forming factors are changed * The vertisol development from aphanitic basalts is determined by the evolution of the structural plateau geomorphic surface through lateral planation, which has allowed for two cycles of pedogenesis* The Mollisols have developed from porphyritic plagio- clase-Olivine basalt* These indicate that soil parent materials with similar mineralogy give way to soil varieties * A lateral variat- ion in some soil properties of the Mollisol order is found to be strongly explained in terms of the slope gradient * The study shows that the Plio-Pleistocene neotectonic uplift and subsequent develop- ment of a deep canyon including morphogenetic threshold slopes has resulted in lack of sufficient time for pedogenic horizons to develop in Alfisols and Entisols *