SEDIMENTOLOGY AND PETROGRAPHY ATTRIBUTES OF OUTCROPPING SEDIMENTS OF COASTAL PLAIN SANDS FROM ABUDU AND ITS ENVIRONS, SOUTHERN NIGERIA

Abstract

Relying on field and laboratory evidences, outcropping sediments at Abudu and its environs were studied for their sedimentological and petrographic attributes. Based on field and sedimentological evidences, two lithofacies, sandstone and claystone were identified in the study area. The claystone facies include two (2) sub-lithofacies of silty clay and sandy clay; while the sand facies include medium to coarse-grained friable sands and, fine to medium-grained sands. Particle size analysis shows sorting values ranging from 0.94 to 2.10 indicating moderately to poorly sorted; skewness values of -0.13 to 0.2 indicating near symmetrical to positively skewed and kurtosis values in the range of 0.77 to 1.34 suggestive of platykurtosis to leptokurtosis. The petrographic analysis reveals the major framework minerals to include quartz (76.9 to 97.5%), rock fragment (0 to 12.9%) and feldspar (0 to 15.4%) and mineral maturity index (MMI) range from 3.8 to 39.0. Poor to moderate porosity was inferred for the sediments. Using field evidences and scatter plots of Skewness versus sorting and mean versus sorting, a fluvial depositional setting was interpreted for the sediments. The sediments range from sub-mature to super-mature; subarkosic to quartz arenites and sediments have undergone intense chemical weathering and/or erosion as evident in the predominance of quartz over feldspar. A craton interior source with contributions from recycled orogen is suggested for the sediments of the study area.