Stratigraphic framework of pulsed volcanism in the central Ethiopian Plateau

Abstract

We present a new stratigraphy of a 50 × 20 km area of the Ethiopian Plateau near Seladingay in northern Shewa province, some 160 km northeast of Addis Ababa. Situated near the rim of the plateau where the Afar depression funnels southwest into the Ethiopian rift, the area consists of > 1200 m of basalt lavas and interbedded rhyolitic volcanics. We describe three detailed stratigraphic sections and establish stratigraphic units on the basis of lithology and thin-section petrography, placed in the context of the regional stratigraphic framework and existing geochronology. We identify and name five new formations, each a package of either basaltic or rhyolitic units. Interlayered sedimentary strata and paleosols attest to intervals of volcanic quiescence. Likely initiating in the Paleogene, volcanism in our study area differs from the coeval Ethiopian Traps both in terms of lava composition and mechanism of magma genesis and extends into the Miocene (~ 15 Ma). From this, we determine that the first four of the volcanic formations in the central Ethiopian Plateau record a unique episode of volcanism in East Africa.