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- Title
Stratigraphic Appraisal and Diagenetic History of the Paleocene Ozuabam Lime-stone in the Afikpo Basin, Southeastern Nigeria.
- Authors
Agumanu, Azuwuike E.; Onyekuru, Samuel O.; Anyanwu, Timothy C.; Onunkwo, Augustine A.; Ibeneme, Sabinus I.; Ubechu, Bridget O.; Nwachukwu, Emmanuel M.; Nweje, Emeke U.; Nwigwe, Chidozie M.; Nwakwesi, Kene C.; Opara, Kelechi D.
- Abstract
The Imo Formation (Paleocene), about 500 m thick cropping out around Umuahia and Okigwe areas, is predominantly clayey shale, mudstone, shale, limestone and sandstone. The formation is exposed at Ozuabam in the Afikpo Basin, southeastern Nigeria. Field investigations, petrology, diagenesis and geochemical analyses were undertaken to evaluate the microfacies characteristics of the carbonates, their depositional dynamics and environmental milieus. They are composed of a 22-m thick alternation of black glauconitic shale and carbonates. Bedded, coarse bioclastic facies overly poorly bedded finer lithology of the unit. Calcimetric analysis permits the differentiation of the carbonates into limestone (>90%CaCO3), marly limestone (65-90% CaCO3) and marl (35-65% CaCO3). The limestone is bioclastic grainstone - packstone, composed of fragmented shells of pauperized and low faunal diversity. The underlying silty and marly mosaic facies, with impoverished organic communities, are essentially wackstone-mudstone. Geochemically and mineralogically, the finer carbonates are more siliceous and dolomitic, respectively. Dolomitization was contemporaneous and related to stylolitization and Mg2+ absorption from illite in the illitic and glauconitic shale interbedding units suggestive of a restricted depositional environment for the carbonates. Early diagenetic imprints included glauconitizaton, fragmentation and micritization while pseudo sparitization, pore cementation and dolomitization represent late diagenesis. The fragmented shells indicate energetic depositional process and correspond to facies 2 and 7 of the carbonate microfacies typifying skeletal sand shoal of lagoon fore slope while the marly facies constitute microfacies 9 and 11 and support deposition within a lagoon shelf.
- Subjects
NIGERIA; PALEOCENE Epoch; BLACK shales; ANIMAL diversity; PETROLOGY; MUDSTONE; PARAGENESIS; MARL
- Publication
Petroleum & Coal, 2024, Vol 66, Issue 1, p276
- ISSN
1335-3055
- Publication type
Article