The Pre-Volcanic Sedimentary Unit in the Kella Section, Western Escarpment, Central Main Ethiopian Rift
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Date
2024-06
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Addis Ababa University
Abstract
In the western flanks of the Central Main Ethiopian Rift (Kella section), the pre-volcanic sedimentary units which are the main focus of this research were investigated. In the present study, a detailed lithostratigraphic section of the area, undertake facies analysis, reconstructing the paleoenvironment, and detailed petrographic characteristics of the pre-volcanic sedimentary units are addressed. Besides; the lithostratigraphic section of the area was correlated with the regional sedimentary work. Detail field investigation and petrographic analysis were used to achieve the objective. Based on field investigation, three sedimentary units were identified. These are sandstone unit, mudstone unit, and carbonate unit. The volcanic unit overlies the sedimentary unit whereas; the basement unit underlies the sandstone unit. 31 rock samples were prepared for thin sections and examined under a petrographic microscope. The petrographic analysis results of 10 sandstone samples show that the sandstone unit is classified into Subarkose, Litharenite, Sublitharenite, and Quartz arenite. Compositionally sandstone unit is mature to supper mature and texturally it ranges from immature to mature. Based on field description and petrographic results, the siliciclastic rocks are classified into 16 lithofacies types and these are classified under 3 lithofacies association groups. The lithofacies associations are Floodplain deposit, meandering river deposit, and Peritidal environment. From the carbonate unit, 20 thin sections were examined under a petrographic microscope. The analysis results reveal that the unit is classified into 12 microfacies types and grouped under 4 microfacies associations. This is sandy mudstone (MF1), carbonate mudstone (MF2), quartz bearings bioclastic packstone (MF3), biosparite Grainstone (MF4), Packstone mudstone (MF5), Oopelbiosparmicrite Packstone (MF6), Daysclad Grainstone (MF7), biomicrite packstone (MF8) bioclastic wackestone (MF9) biomicrite wackestone (MF10) and bioclastic mudstone (MF11), and Radiolarian wackestone (MF12). The microfacies association of the carbonate unit is classified into three groups. Thus are; facies association 1 (MF3, MF10, MF11), facies association 2 (MF6, MF7, MF9), and facies association 3 (MF1, MF2, MF4, MF5, MF8). Generally, the carbonate unit described in the Kella section was deposited in the shallow marine environment. The overall facies stacking pattern of the study area led to the conclusion of continental to shallow marine environment.
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Keywords
Depositional Environment, Kella Section, Lithofacies, Microfacies, Petrography