The International Commission for Stratigraphic Classification (ICSC) has standard laid out procedures, policies, and rules for naming lithologic unit and these criteria do not include diagenetic changes as a basis for naming formation. The upper strata unit of the Ameki Group with respect to facies relation creates uncertainties in the stratigraphic nomenclature. This study using multi-element geochemistry of relatively immobile rare earth elements narrowed the knowledge gap by interpreting and unifying sediment source area of Upper Ameki Group. The “Nsugbe” sandstone is a diagenetic product of the “Nanka” sands and this further simplifies the stratigraphy of Upper Ameki Group. Consequently, this research identifies the need to synchronize or review the nomenclature in line with ICSC guidelines.