Structural Features of Ajali Sandstone in the Western and Eastern Parts of River Niger, Southern Nigeria

Abstract

The small-scale structural features identified in the field are original sedimentary structures. They were formed as direct results of sedimentation processes and are clearly preserved. The size, shape, and sorting of sedimentary structures within rocks may provide clues to the depositional environment that existed during their formation. They yield evidence of the top and bottom of individual beds and include graded bedding at Agola, current bedding at Fugar, ripple marks and sole marks at Fugar and Okigwe areas. The inclined beds are not due to secondary structures of tectonic origin, but the surfaces on which the original sediments were deposited. It varies from 4° SE at Ihube Okigwe to 7° S at Fugar, Edo state. The presence of Ophiomorha and Skolithos ichnofacies indicates marine environment although Ajali Sandstone is believed to be predominantly continental. Also it shows very poorly sorted and no graded bedding at Fugar, and this points to high-energy environment and current bedding. The Ajali Sandstone has several dome-shaped and circular highlands capped by laterites. The spring water that occurs at the contact between the Mamu – Ajali boundaries are structurally controlled.