Textural Characteristics And Heavy Mineral Analysis Of Surficial Sediments From Parts Of Igangan Sheet, Southwest Nigeria: Implication For Depositional Processes And Provenance Interpretation

Abstract

Grain size and heavy mineral analyses were carried out on some surficial sediment (colluviums and stream sediments) collected within parts of NW Igangan sheet with the aim of characterizing the depositional processes and provenance. A total of twenty five (25) samples were subjected to sedimentological analyses including lithological description, textural analysis, heavy mineral separation and petrological identification of heavies recovered.  Results show that the sediments were angular to sub-rounded and grain sizes ranged from granules to fine grain sediments. The sediments ranged from poorly sorted to moderately well sorted (0.66-2.08 ϕ); and have kurtosis  and skewness values ranging from 0.81 to 8.65 ϕ and -7.27 to 3.83 ϕ suggesting platykurtic to leptokurtic, and strongly coarse skewed to strongly fine skewed sediments respectively. With a total of 2289 heavy mineral counts, 49.6% were non-opaque and were used in heavy mineral analysis. The dominant heavy minerals were zircon accounting for 22.3%, tourmaline (18.0%) and rutile (13.1%). Zircon-Tourmaline-Rutile index computed for the samples ranged from 52% – 70% suggesting moderate maturity of the sediments. Other varieties of heavy minerals observed apart from the opaques include hornblende, garnet, glaucophane, staurolite, apatite and Kyanite. Such assemblage reflects a mixed source of igneous and metamorphic provenance most probably of the surrounding south-western Nigerian basement complex. Most of the heavy mineral were near euhedral in form and retain their original habit while some others appeared sub-rounded indicating short travel distance from provenance. Deductions from bivariate analysis were consistent with the environmental regime responsible for transportation of the sediment since they all point to fluvial environment