Micro facies analysis and depositional environments of the carbonate unit in the Blue Nile Basin, Central Western Ethiopia

This study presents a detailed analysis of the facies and paleoenvironment of the 330 m-thick carbonate unit in the Mertule Mariam section, Ethiopia. Fifty-five (55) samples were selected for lithostragraihical and petrographic analysis from the carbonate unit. Lithostratigraphically, the unit is characterized by marls, calcareous shales, micritic, oolitic, fossiliferous and bioturbated micritic limestone. On the basis of petrographic investigations, seven (7) microfacies types are identified: Bioclastic-Intraclastic packstone/grainstone, Peloidal grainstone, Oolitic packstone / grainstone. Dolomitized packstone, Coral Framestone, Bioclastic packstone / grainstone and Bioclastic mudstone. In order to reflect dispositional energy conditions, the microfacies were grouped into three microfacies associations: (i) High-energy shallow marine environment (MFT1, MFT2 and MFT 3) (ii) Shallow marine to Reef environment associations (MFT5 and MFT6), and (iii) Low-energy, restricted marine environment associations (MFT4 and MFT7).