Petrography of Ajali Sandstone in Ayogwiri – Fugar – Orame Area of Western Anambra Basin: Implication for Diagenetic and Depositional History.

Abstract

The friability of the Ajali Sandstone was studied with photomicrographs of thin sections made from samples collected from the Formation in Ayogwiri, Fugar and Orame in the Western Anambra Basin in order to understand its diagenetic and depositional implications. This study shows that the Ajali Sandstone is a quartz arenite consisting of subangular to subrounded grains of quartz which were either monocrystalline or polycrystalline. Diagenetic fabrics of compaction, dissolution, alteration and corrosion were common features. Straition marks, fracture lines, some of which show filling, stress zonation were major compaction fabrics in the Sandstone. Authigenic quartz formed from the dissolution and recrystallization of quartz grains as well as quartz overgrowth occur. Reaction rims around grain margins indicating severe alteration and corrosion were seen growing from grain margins inward, leaving the Sandstone, which may have been indurated with little or no cementing material. Thus leading to the friability of the Sandstone and it’s susceptibility to erosion.

Keywords: Petrography, Diagenesis, Authigenesis, Decementation, Cementation, Dissolution, Alteration, Corrosion,