Provenance analysis of Campanian-Maastrichtian sediments, Anambra Basin, Nigeria: Evidence from garnet and tourmaline mineral species and paleocurrents

Abstract

Electron microprobe analyses of garnet and tourmaline heavy minerals and paleocurrents were carried out in the three rift-related Campanian-Maastrichtian sedimentary formations of the Anambra Basin, Nigeria. This study revealed the existence of an almandine-rich end-member garnet that yielded a PyrAlSpite group (pyrope, almandine, and spessartine) in the study area. Furthermore, the tourmaline grains belong to the alkali and calcic groups which are dominantly composed of dravitic and magnesio-foititic (uvite) tourmaline compositions. High Mg/Fe and Na/Ca ratios indicate medium to high-grade metamorphic source rock derivatives. The integration of garnet and tourmaline data and different binary and ternary discriminant plots show that the precise source rocks of the rift-related sedimentary formations of the Campanian-Maastrichtian, Anambra Basin, Nigeria in the study area were mostly from medium to high-grade basement rocks consisting of andesite, mica-schists, chlorite schists, amphibolites, marble, quartzite, gneisses, metabasic-subophiolitic, granulitic, rhylotic, and aplitic facies and minorly low-grade metasedimentary rocks associated with metacherts, blue-schists, metapelites, phyllites, marbles, and metapsammites. The paleocurrent interpretation reveals that the sandstones were derived from the tectonically restricted Nigerian Precambrian Pan-African Basement Complex and uplifted Benue Trough.