Volcanism, sedimentation, K/Ar and palynology studies, Yayu and Delbi-Moye Basins, Southwestern Plateau of Ethiopia

Abstract

Major element, K/Ar, sedimentation and palynology data are reported on Tertiary volcanic and sedimentary rocks from the Yayu and Delbi-Moye Basins, SW Ethiopia. In the Yayu and Delbi-Moye Basins, pre-rift volcanic (basalts) and post-rift volcanic (basalts) are separated by coal and oil shale-bearing sedimentary rocks. The basalts are tholeiitic in composition. The K/Ar data on the volcanic rocks range from 10.98 ± 0.55 Ma (Lower Miocene i.e. Tortonian) to 111.19 ± 2.83 Ma (Early Cretaceous i.e. Aptian). Inter-Trappean coal and oil shale-bearing sedimentary rocks are widely distributed in the Yayu and Delbi-Moye Basins. The NNW–SSE fault system developed grabens and half-grabens for the deposition of coal and oil shale-bearing sedimentary rocks. The sedimentary successions are dominated by fine to medium-grained sandstones, siltstones, mudstones, carbonaceous shales, carbonaceous claystones, coal and oil shale seams, and are characterized by meandering river and lacustrine...