Characterization of Diagenetic Processes of the Late Maastrichtian – Danian Limestones in Ohafia, Ozu Abam and Arochukwu Areas of Southeastern Nigeria

Abstract

Vast deposits of limestones of Late Maastrichtian to Paleocene age occur in the Ohafia, Ozu-Abam and Arochukwu areas of southeastern Nigeria. The present study sought to gain insight into the evolutionary history and conditions of formation of the limestones, through detail investigations and characterization of the diagenetic processes that affected the rock. The diagenetic processes considered include cementation, neomorphism, micritization, compaction and dissolution. Dolomitization process was not considered because it was conspicuously absent in all the thin sections examined. The cement types observed include blocky or equant mosaic calcite cement, drusy mosaic calcite cement, micritic calcite cement with a meniscus fabric, and acicular aragonite cement. Micritization of bioclasts in the limestones is very low and is characterized by thin micritic envelopes covering the grain surfaces. Neomorphism is a prominent feature of the limestones and is responsible for the formation of large sized crystals in the limestones. Compaction is discernible by a parallel alignment of fractures in a thin section. Dissolution in the limestones is shown by the presence of solution cavities in the thin section. Dolomitization were not observed in the limestones. The various diagenetic transformations that the Late Maastrichtian to Paleocene limestones of Ohafia, Ozu-Abam and Arochukwu areas of southeastern Nigeria have undergone corroborates development under shallow marine conditions. In particular, the presence of drusy mosaic as a cement type is an indication of the relevance of meteoric phreatic conditions in the evolutionary history of the rock.

Keywords: Diagenesis, Carbonate, Petrography, Nigeria