© Emerging Academy Resources www.emergingresource.org 7 DEPOSITIONAL ENVIRONMENT, GEOPHYSICAL MAPPING AND RESERVE ESTIMATION OF LIMESTONE DEPOSIT IN ARIMOGIJA- OKELUSE AREA,

The shale – limestone sequence at Arimogija – Okeluse belong to the Cretaceous Abeokuta Formation deposited during the first marine transgressive cycle in the Dahomey basin. Petrographic study was carried out to identify skeletal and non – skeletal grains for the determination of depositional environment. Detailed geophysical mapping of the area using Vertical Electrical Sounding (VES) was applied to establish the thickness of the different subsurface layers. The limestone horizons were delineated and reserve estimated. The skeletal grains identified include: brachiopods, bivalves, gastropods, ostracods, echinoids and broken shell fragments while non-skeletal grains are ooids and pisoids. Micrite and sparry calcite are found to be abundant and are the dominant microfacies. The VES results reveal 3 to 4 geo-electric layers which include: the clay / lateritic top soil, limestone and shale. The reserve volume of the limestone in the Arimogija area is approximately 1.3 x 108 tonnes while Okeluse area stands at approximately 3.04 x 108 tonnes for areas of 10.4 x 106 m2 and 4.7 x 106 m2 respectively. This study indicates that the limestone reserves in the Okeluse area exceeded that of the Arimogija area. It will be cost- effective to set- up a cement factory in the Okeluse axis due to its possession of a substantially larger portion of the limestone reserves. Petrographic features observed in the limestone microfacies suggest quiet water, low energy, and open shelf environment