Petrological and Geochemical Evaluation of the Paleocene-Eocene Lithofacies in Dahomey Embayment, Southwestern Nigeria
For a geologist, his main work is to study Earth processes, Earth materials and Earth history, which will help
people to understand our planet better. And there are many more detailed fields
in geology that different geologists focus on in the same place.
Dahomey Basin is an arcuate coastal basin, the onshore parts of which underlie the
coastal plains of southwest Nigeria, Benin and Togo. In this paper, the study
area is located in Ibese, southwestern Nigeria about 40 km southwest of
Abeokuta. And the authors focused on the distribution of diverse lithofacies,
genetic description of the Ewekoro Formation with emphasis on the limestone and
what characterize the environment of its deposition, the extent of diagenesis,
biological influence on the chemistry of the units, major elemental
composition, post depositional processes and their viability in determining its
economic values.
The field mapping was carried out in order to determine different rock
units and their association within the area. The collected samples were
disaggregated and subjected to lithological description and petrography in the laboratory
while the samples for the XRF analysis were pulverized into a fine powder. The
authors analyzed the lithostratigraphy, geochemistry, carbonate petrography and
depositional palaeoenvironment of the study area via the samples.
The findings indicated that the total thickness of the limestone
ranged from 12.0 m to 15.0 m. And the limestone consists of milky to grey and
nodular to massive fossiliferous limestone units while the sand content
increases with depth. The composition of the major oxides in the thirty-seven samples
from six exploratory wells revealed that CaO, SiO2, Fe2O3 ,
MgOand Al2O3 were the most abundant elements. The
trend of the geochemical indices showed increase in the percentage composition
of CaO, and MgO. And the percentage composition of Al2O3,
Fe2O3 and K2O were significant indicating
continental influence during diagenesis and diverse depositional episodes. The
three different microfacies recognized based on depositional texture are shelly
biomicrite, shelly biosparmicrite and alga biosparmicrite. The predominance of
micrite as the cementing matrix revealed that the rock was deposited in a quiet
shallow inner shelf environment occasioned by storm waves.
Article by Olugbenga A. Boboye and
Olusegun J. Omotosho, from University of Ibadan,
Ibadan, Nigeria.
Full access: http://mrw.so/1cH1WU
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| Image by joel, from Flickr-cc. |
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