Relation Ship Sbetween Geology Mor Phology And Soil Associations Of Bichena Area ( S. E. Gojam )

The study investigates the extent of influence of the geolog- ical history , essentially parent rock * topography and time , onrnsoil formation and distribution in Bichena , Southeastern Gojjam *rnLithostratigraphy of the Mesozoic sedimentary sequence andrnCenozoic volcanics is described * An attempt has been made tornreconstruct the morphologic evolution of the area * Four soilrnmapping units in close relationship with the parent materialrnand geomorphology have been differentiated: Vertisol, Mollisol,rnAlfisol and Entisol Orders 0 The soils are found to assume differentrnstates when the above considered soil forming factors are changed *rnThe vertisol development from aphanitic basalts is determinedrnby the evolution of the structural plateau geomorphic surfacernthrough lateral planation, which has allowed for two cycles ofrnpedogenesis* The Mollisols have developed from porphyritic plagio- clase-Olivine basalt* These indicate that soil parent materialsrnwith similar mineralogy give way to soil varieties * A lateral variat- ion in some soil properties of the Mollisol order is found to bernstrongly explained in terms of the slope gradient * The study showsrnthat the Plio-Pleistocene neotectonic uplift and subsequent develop- ment of a deep canyon including morphogenetic threshold slopes hasrnresulted in lack of sufficient time for pedogenic horizons to developrnin Alfisols and Entisols *

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