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Vol.4 , No. 2, Publication Date: Jun. 9, 2017, Page: 19-27
| [1] | Ezekiel Obinna Igwe, Department of Geology, Ebonyi State University, Abakaliki, Nigeria. |
Lithofacies study of tidalites in six localities within the Ajali Formation, Anambra-Afikpo Basin complex of southeastern Nigeria was carried out to interpret depositional environments and model for the unit. The study involved identification and description of outcrops, and lithofacies characteristics of tidalites noting sedimentary structures in the outcropping facies. Six lithofacies typically of tidally-influenced shelf setting and tidal current processes characterized the Ajali Formation. The medium to coarse grained planar and trough cross bedded sandstone lithofacies, fine to medium grained planar cross bedded sandstone lithofacies, herringbone cross bedded sandstone lithofacies are deposits of subtidal sandwaves under high energy phase associated with tidal flow regime. The cross/ripple laminated heterolithic facies and horizontal laminated/bedded sandstone lithofacies were deposited in tidal flats, shallow shelf setting under low current energy. The bioturbated sandstone lithofacies with Skolithos isp was deposited in low energy intertidal zone. These interpretations are corroborated by occurrence of tidally-influenced sedimentary structures in the studied formation. These include tidal bundles, herringbone cross stratification, mud draped foresets, reactivation surfaces, flaser beddings, ripple and horizontal laminations and biogenic trace fossil suites consisting dominantly of Skolithos ichnofacies. Overall, these lithofacies indicate deposition in tidal flat and tidal sandwaves in shallow shelf depositional environments.
Keywords
Tidalites, Lithofacies, Ajali Formation, Depositional Environment
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