Topography and Particle Size Gradation Characterization of the Benin Formation in the Lower Niger Delta, Nigeria

摘要

The Benin Formation as a significant geologic unit of the Niger delta is well known. However, its importance in engineering geology, as a veritable source of construction material and foundation layer to many civil structures is hardly discussed. This study utilized the records from over 250 geo-referenced boreholes distributed mostly on linear alignments to the east and west of the Niger delta to generate the surface longitudinal profile of the Benin Formation in both the west and the eastern sections of the Niger Delta. In addition, particle size gradation characteristics of the sediments were analyzed to detect possible trends that reflect the predominant mechanisms of transportation. The study shows an initial steep gradient from Agbor to Sapele to the west, followed by a gentler and almost flat profile, with occasional depressions that are infilled with silty clay sediments, that may be linked to buried river channels. To the east, the longitudinal profile mirrors the ground surface, with a gradient approximating 1.91x10-4 as a first step in determining the depth to sand in the study area. The particle sizes within the depths of civil engineering significance (0-40m), show a tendency of upward fining. The Uniformity coefficients show some constancy, suggestive of similar environmental and energy conditions of deposition.