Lithofacies Analysis and Depositional Environment of Eocene – Paleocene Sediments of Ewekoro Quarry SW, Nigeria

Abstract

The genetic relationship between depositional processes and rock properties (like lithofacies) provides a potentially powerful tool for interpreting ancient depositional environments. The study aims at a more detailed lithologic and petrographic description of the sediments of this formation in other to ascertain the chemical characteristics of the limestone so as to better delineate its uses both industrially, agriculturally and in other applications. Seven samples were collected from Ewekoro quarry on the latitude of 6⁰ 48’ N - 6⁰ 53^’ N and Longitude of 3⁰ 35^’ E - 3⁰ 40^’ E south western part of Nigeria. The sediments were subjected to lithologic description and petrographic analysis. The lithologic description was carried out with the aid of a binocular microscope, which shows the following lithologies: sandy shale, shale, marl, limestone, and sandstone. Petrographic analysis shows that the limestone consists of 90-99% calcite, 0-2% quartz as its constituent minerals, sample NSA2 is mainly Sparitic limestone and sample SSA1 is mainly Micritic limestone. The sandstone composition is 50-65% quartz, 0-5% feldspar and the calcite which serves as the cement is about 10-32% of the rock volume. Microfossils account for 10-18%. The sediments were deposited in a shallow environment based on the presence of ichnofossils (burrows), micro gastropod shells and other broken shells. From the mineralogy, the calcite crystals suggest a freshwater vadoze environment while the Sparry calcite shows evidence of diagenesis within the formation. The relative age of foraminifera present indicated a Palaeocene/Eocene boundary to Lower Eocene and a lagoonal to the inner neritic environment with little influence of marine transgression. Ewekoro limestone is well suited as a raw material for fertilizer besides its general usage for cement manufacturing.