Petrography and Heavy Mineral Studies of the Eocene Sediments in Awka and Environs, Southeastern Nigeria: Implication for Provenance

Abstract

Petrography and heavy mineral techniques were employed in the study of the Nanka Formation in order to evaluate sediment provenance and tectonic setting. Petrographic study of the sands shows that quartz is the dominant mineral (64- 85%) with high monocrystalline to polycrystalline quartz ratio, feldspars vary from 1- 4%, rock fragments range from 1 to 15% whereas matrix is between 8 and 15%. The framework grains are medium to coarse in size, sub-angular to rounded and moderately well sorted to poorly sorted. Quartz grain abrasion and grain coating with iron oxide together with the framework grains that are devoid of cement are characteristics of the sands. The QFL ternary plot indicates that the sands are quartz arenites and sublitharenites. Maturity evaluation shows them to be texturally submature to mature and mineralogically submature to supermature. Heavy mineral assemblages consisting of zircon, tourmaline and rutile with sub-rounded to rounded grains were recovered from the sands. The QFL and QmFLt ternary plots of the sands indicate derivation from Craton Interior, Recycled Orogen and Quartzose recycled. Metamorphic and plutonic rocks of Oban Massif and the sedimentary rocks of the Benue Trough and Anambra Basin are suggested as parents. Weathering of the source rock took place under semi- humid to humid climatic conditions in a low relief.