Sedimentological and Geochemical Analysis of Sediments in the Excavated Rock Shelter at Fincha Habera Section, Bale Mountain, Southeastern Ethiopia: Implications on Provenance (Source) and Depositional History

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Addis Ababa University


This study is about the provenance and depositional history of clastic sediments deposited in a rock shelter at the Bale Mountains, Southeastern Ethiopia. The sediment section has been excavated for archaeological study. Sedimentological and geochemical characteristics of the sediments in the Fincha Habera section, at the excavated rock shelter site have been investigated. A total of 22 sediment samples have been collected and analyzed, and the analysis results are used to determine the provenance (source) and depositional history of the sediments. The grain size analyses of the unconsolidated sediments show that the sediments range from fine to coarse (silt to silty sand) with mean particle size ranging from 11.97 to 140 μm, poorly to very poorly sorted, with standard deviation of most samples ranging from 1.829 to 5.12 μm; very fine skewed to very coarse skewed with skewness ranging from -0.378 to 0.396 μm, and platykurtic to very leptokurtic with kurtosis ranging from 0.709 to 1.537μm. The relationship between the mean grain size and sorting suggests that sedimentation took place in high energy, open fluvial depositional environments. The integrated data from the field (lithofacies associations), sedimentological analysis (grain size and magnetic susceptibility measurement), and geochemical analysis (elemental and mineralogical compositions) of the sediments has been used as a combined proxy for provenance determination. Accordingly, the integrated data suggest that the materials/sediments that are deposited in the rock shelter have a mixture of three sources: geogenic (either as endogenic or exogenic), biogenic or human induced (anthropogenic) origins. The grain size analysis (sorting), the log ratio of major elements (low log (SiO2/Al2O3) value), the less mobile major elements (Al2O3 and TiO2) ratio, and the mineralogical composition (i.e., predominantly of plagioclase feldspars, particularly anorthite and albite) suggests that the geogenic materials are texturally as well as chemically immature and derived predominantly from mafic source rocks. The magnetic susceptibility of the sediments is indicative of either the anthropogenic sources of some layers in the section, or significant accumulation of organic matter, as the combustion/heating of the sediments by anthropogenic activities or occurrence of sizable quantity of organic matter such as ash and charcoal deposits, respectively, can affect the magnetic susceptibility value. Furthermore, the magnetic susceptibility value of the sediments can be correlated with the Ca and P concentrations (indicators of biogenic materials).



Bale Mountain, Fincha Habera, Sedimentology, Provenance, Depositional Environment, Grain Size Distribution