地球科学と気候変動ジャーナル

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Evaluation of Pebble form Indices as Paleoenvironmental Signatures of the Maastrichtian - Danian Age Using Quartz Clasts in Owerre-Ezukala Area, Southeast of Nigeria

Chidera Ikechukwu V, Okpoko Ephraim I and Egbunike Michael E

The Maastrichtian - Danian age is well exposed around the Owerre-Ezukala area in the Anambra Basin of southeastern Nigeria. Two geologic units were encountered in the study area; Maastrichtian Ajali Formation and Danian Nsukka Formation. Outcrop sections were located, measured and described in detail following standard field methods. Pebble beds were sampled to evaluate their form indices which served as signatures of the paleoenvironment of deposition. The research methodologies were standard methods used in pebble morphological analysis. A total of one hundred and thirty pebbles were collected from three localities (Olo, Owerre–Ezukala and Ubaha). The following parameters were evaluated; Flatness Index (FI), Oblate-Prolate Index (OPI), Pebble form and Maximum Projection Sphericity (MPS). The mean values of FI, OPI and MPS (44.7%, -0.066, and 0.789 respectively), are suggestive of a fluvially agitated shallow marine environment (estuarine). Bivariate scatter plots of FI versus MPS and MPS versus OPI suggest fluvio-estuarine environment. Plots made on sphericity-form diagram suggest a transitional setting (probably fluvial to estuarine). The sedimentary facies analysis supports a fluvio-estuarine setting for the Maastrichtian – Danian age.