Micropaleontology and Facies Analysis of Carbonate Unit in Mugher Area (Sodoble Section), North Western Ethiopia
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Date
2008-05-03
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Addis Ababa University
Abstract
Thick layers of Jurassic carbonate unit (Antalo Formation) which were deposited in Mugher area (Sodoble section) were investigated in field and lab analysis. This study mainly aimed on exploring the micropaleontology, facies analysis, biostratigraphy and determination of the depositional environments of carbonate unit in sodoble section. Through field observation the detailed Lithostratigraphy of sodoble section carbonate successions of the area, was described and measured at three locally selected stratigraphic sections. At all these three local sections, the exposed carbonate layers are described based on their facies types and are sub-divided into three sub-units. Based on the petrographic study of 26 representative carbonate rock samples collected from the study area; the compositional and textural types of rocks were studied and grouped into seven microfacies types. Paleontological study of Sodoble section in Abay basin shows that the carbonate unit is rich in macro and microfossils. From those there are many benthic foraminifera like: Lenticulina subalata, Lenticulina quenstedti, Kurnubia palastiniensis, Nautiloculina olithica, Verneuilinoides minuta, Haplophragmoides bartensteini, Pseudocyclammina lituus and Alveosepta jaccardi are identified at species level as well as some bivalves, gastropods and brachiopods and ostracods are identified at genus level.
Based on the presence of index fossils of Pfenderina gracilis, Kurnubia palastiniensis and Alveosepta jaccardi, age of sodoble section carbonate rocks is assigned as Callovian to Kimmeridgian time. The general successive facies and facies belts of the carbonate units of Sodoble section from field investigations and microfacies analysis results shows entirely shallow marine water environment. It shows transgression from tidal environments of the inner ramp at the base with occasional interrupted episodes indicating a relatively high-energy environment to relatively low energy deep margin environments of the outer ramp at the top of the succession. The carbonate deposits of the section are correlated with some of equivalent deposits in Northwestern and other regional sedimentary basins of Ethiopia based on their Lithostratigraphy and chronostratigraphic relationship.
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Depositional Environment, Fossil, Microfacies, Facies, Paleontology, Sodoble section, Northwestern Ethiopia Plateau