Microfacies, Diagenesis and Depositional Environment of the Cenomanian – Turonian Gongila Formation, Bornu (Chad) Basin, Northeastern Nigeria

The Gongila Formation in the Bornu Basin is represented by a succession of interbeds of shales and limestones, and these limestones facies consist of packstone (pack biomicrite), wackestone (sparse biomicrite), mudstone (micirte) and extraclast biofacies. The packstone and wackestone microfacies may possibly have been formed in an inner to middle shelf environment with relatively low energy conditions while the mudstone biofacies must have formed under quiet water lagoonal environment. The extraclast biofacies may suggest periods of erosion which might have occurred during relative sea level fall that must have exposed the limestone facies subareial conditions. These limestone facies have undergone different phases of diagenesis which include micritization, dissolution, neomorphism and calcitization and this has altered the original fabric of the limestone, leading to the development of moldic and vuggy porosities in some of the limestone facies.