Microfacies analysis and depositional environment of limestone deposits: Arochukwu – Obotme – Odorikpe axis southeastern Nigeria

Microfacies analysis of limestone deposits from Arochukwu – Obotme – Odoro Ikpe Axis has been carried out complimented with biostratigraphic and sedimentological analysis. Fieldwork and Laboratory techniques employed are standard methods as used in limestone petrography (preparation of the limestone thin sections), sedimentological and biostratigraphic studies. Petrographic analysis results indicate that the limestone is made up of between 80% and 60% allochems while cements make up between 19% and 38% respectively. The allochems consists of shell fragments, whole pelecypod shells, algal grains, diatoms, foraminiferids, whole gastropods shells, bryozoans, ostracods, crinoids and coral fragments in addition to ooids/peloids, quartz grains, intraclasts and phosphate grains that make up the limestone. The cement type is interpreted as sparite and porosity type is interparticle and fracture. Important fossils identified in the limestone samples include Anomalinoides sp, Textularia sp, ostracods, pelecypods, gastropods and corals which occur either as whole skeletal forms or as fragments. Based on the microfacies characteristics, the limestone in the study area are sandy bioclastic packstone, bioclastic packstone and bioclastic wackstone bioclastic wackstone / bioclastic packstone at Locations 5 (Amuvi), (Obotme) – 2, (Asaga) 3 and 4 (Okobo) and sandstone with about 10% shell fragments at Location 2 (Odoro Ikpe), – sandy bioclastic packstone. Two microfacies identified in the study area which correspond to SMF 5 and SMF 9. The environment of deposition is interpreted as normal marine, subtidal to shallow shelf which is consistent with shallow inner neritic to middle neritic interpreted from biostratigraphy (foraminifera and palynomorphs) identified in the limestone and associated shale samples.