International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:12 No:04 6 120404-8585-IJBAS-IJENS © August 2012 IJENS I J E N S Abstract-- The New Netim Formation located in the Calabar Flank, South Eastern Nigeria is made dominantly of bedded / nodular marlstones interbedded with thin beds of shales. In the Calabar Flank, this marl unit forms extensive ridges and hills from the Mbebu village in the Southeast to Ikot Nyong in the Northeast. This carbonate build up is being investigated to elucidate its lithostratigraphy, microfacies, sequence stratigraphy and depositional environment. Being located between the Gulf of Guinea and the Aptian Salt Basins in the South Atlantic, this study will give a clue on the rhythms of the Coniacian transgression in the South Atlantic. Carbonate analysis reveal the predominance of three major microfacies type, which recur continuously both vertical and horizontally. The identified microfacies types are: biomicritic mudstone – wackestone, micritic mudstone and pelmicritic mudstone microfacies. Sequence stratigraphic analysis based on inferred sea level changes, shows that the marl unit is an aggradational sequence stratigraphic unit with continuous “pendulumic” fluctuations in sea levels between shallow and deep marine environment during the Coniacian transgression in the South Atlantic. This is evident by monotonous repetition and similarity of facies composition in each successive parasequence with relatively minor facies shift and no clear long term trend. Inferred depositional environment based on microfacies and sequence stratigraphic interpretations indicate deposition in a low energy, lagoonal / protected bay environment with continuous and repetitive sea level changes between shallow and deep marine. Index Term-- lithostratigraphy, carbonate microfacies, depositional environment, sequence stratigraphy, New Netim Formation,Marlstones. NSE U. Essien is serving in Department of Geology, University of Calabar, Nigeria nseessien@yahoo.com Edoho D. Bassey is serving in Department of Geology, University of Calabar, Nigeria I. INTRODUCTION The New Netim Formation composed dominantly of bedded / nodular marlstones interbedded with thin beds of shales in the Calabar Flank (Fig.1), Southeastern Nigeria was erected during the stratigraphic revision of Petters et al, (1995). The Calabar Flank is located at the extreme of the Gulf of Guinea and adjoins of the South Atlantic Aptian Salt Basins (Fig.2). It is separated by the Douala Basin (Cameroon) by the Annobon – Cameroon volcanic line formed during the Early Cretaceous. This fracture zone is the northern – most limit of the Aptian Salt Basins and served as a barrier that prevented the extension of the Aptian Salt Basin into the Gulf of Guinea. The Calabar Flank though at the boundary between the Gulf of Guinea and the Aptian Salt Basin, shares common structural and stratigraphic characteristics more with the South Atlantic Aptian Salt Basins than adjoining sedimentary basins (Gabon, Kwanza, Congo, Kiribi- Capmo etc ) in the Gulf of Guinea. The structural elements (horst and grabens) of the Calabar Flank are aligned in a NW – SE Direction like those of other South Atlantic marginal basins in West Africa. The Calabar Flank show striking stratigraphic similarities with coeval marginal basins in the South Atlantic. They all were formed during the opening of the South Atlantic. Thus, the Coniacian New Netim Formation can be correlated with Mungo Formation (Limestone with salt intrusive) in the Kribi – Campo basin, the Madingo Marl (post – rift lacustrine marl and shales with lenses of siltstone) in the Congo basin and the Upper unit of the Itombe Formation (limestone, shales and siltstone) in the Kwanza Basin in Angola. In Nigeria, while marlstone was deposited in the Calabar Flank during the Coniacian, limestone beds of the Nkalagu Limestone was deposited in the adjoining Benue Trough. This investigation is an elucidation of the lithostratigraphy, microfacies analysis, sequence stratigraphy and the determination of the depositional environment of the Coniacian New Netim Marl. It is also an attempt to understand in the Calabar Flank the rhythms of the Coniacian transgression in the South Atlantic. Lithostratigraphy, Microfacies Succession, Sequence Stratigraohy and Depositional Environment of The New NETIM Formation, Calabar Flank,South Eastern Nigeria. NSE U. Essien and Edoho D. Bassey