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<p>Limestone from the Ewekoro Formation in the Dahomey Basin was studied for its elemental and stable isotope (carbon and oxygen) composition. This is aimed at determining their diagenetic, depositional environments, source of REE, detrital influx, and its sources. The limestone is calcitic in nature, evident from its high CaO (Range from 27.00 to 53.10 wt%; Av. 45.63 wt%) value, this was followed by SiO<sub>2</sub> and Fe<sub>2</sub>O<sub>3</sub>. Enriched in Sr (Av. 137.7&#xa0;ppm) supporting calcitic nature, although, below the normal lithosphere carbonate (610&#xa0;ppm), suggest diagenetic alteration. Bivariate plots of ΣREE Vs CaO and Al<sub>2</sub>O<sub>3</sub> Vs TiO<sub>2</sub> with ratios of La/Sc, La/Co, Th/Sc, Th/Co, and Th/Cr confirms that felsic source rocks account for the majority of the detrital input. Although computed depositional setting (Z) indicates that possible marine environment cannot be ruled out, the Y/Ho ratio revealed that the studied limestone samples preserved more of terrigenous constituents and volcanic ash water than sea water signs. The plot of δ<sup>13</sup>C vs. δ<sup>18</sup>O and the estimated paleo-temperature (T) of 34.21&#xa0;°C, suggest a warm environment for its deposition, with precipitation mostly originating from fresh water sources. Thus, Ewekoro limestone is a diagenetically altered limestone, calcitic in nature, deposited during a warm climatic condition that precipitated from more of fresh water under an oxic depositional environment but suffered contamination from detrital materials derived of felsic source rocks.</p>

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Possible sources of REE, Paleo-redox conditions, and diagenetic history of Paleocene limestone from Ewekoro formation, Eastern Dahomey Basin, Southwestern Nigeria

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  • 发表日期：

    2025年6月26日

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  • R. G. Oladimeji,
  • S. O. Idakwo,
  • M. A. Adeleye,
  • A. Musa

摘要

Limestone from the Ewekoro Formation in the Dahomey Basin was studied for its elemental and stable isotope (carbon and oxygen) composition. This is aimed at determining their diagenetic, depositional environments, source of REE, detrital influx, and its sources. The limestone is calcitic in nature, evident from its high CaO (Range from 27.00 to 53.10 wt%; Av. 45.63 wt%) value, this was followed by SiO2 and Fe2O3. Enriched in Sr (Av. 137.7 ppm) supporting calcitic nature, although, below the normal lithosphere carbonate (610 ppm), suggest diagenetic alteration. Bivariate plots of ΣREE Vs CaO and Al2O3 Vs TiO2 with ratios of La/Sc, La/Co, Th/Sc, Th/Co, and Th/Cr confirms that felsic source rocks account for the majority of the detrital input. Although computed depositional setting (Z) indicates that possible marine environment cannot be ruled out, the Y/Ho ratio revealed that the studied limestone samples preserved more of terrigenous constituents and volcanic ash water than sea water signs. The plot of δ13C vs. δ18O and the estimated paleo-temperature (T) of 34.21 °C, suggest a warm environment for its deposition, with precipitation mostly originating from fresh water sources. Thus, Ewekoro limestone is a diagenetically altered limestone, calcitic in nature, deposited during a warm climatic condition that precipitated from more of fresh water under an oxic depositional environment but suffered contamination from detrital materials derived of felsic source rocks.