Stratigraphic and lithofacies analysis of the Gohatsion Formation in the Blue Nile basin, central Ethiopia: Implications for depositional setting

Abstract

The Gohatsion Formation consists of a cyclic intercalation of fine siliciclastic and evaporite/carbonate beds and has been subdivided into three informal members, namely the Lower Mudrock Member, the Gypsum Member and the Upper Mudrock Member. Four lithostratigraphic sections were constructed at the Gohatsion, Dejen, Mugher and Jemma localities. Lithofacies analysis of the succession at outcrop and petrographic scales indicate a broad tidal belt influenced by seasonal and regional climate and sea level changes. Integrated lithofacies depositional models for the corresponding informal members have been proposed in order to demonstrate the lithological response to local and global climate change and sea level fluctuations that occurred during the initial phase of the Tethyan Sea transgression during the early to middle Jurassic. Lithofacies of the Lower Mudrock Member show deposition within a siliciclast-dominated back barrier tidal flat system. Deposition of the Gypsum Member occurred in a marine coastal sabkha belt, whereas the Upper Mudrock Member was deposited in a broad coastal shelf prone to seasonal marine flooding. The models show that all the members of the Gohatsion Formation were formed within a broad coastal tidal belt with continental influence and sediment delivery from the northwest, and a slowly encroaching transgressive marine influence from the southeast.