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This research work is the detailed facies analysis of the depositional environments and paleogeographic setting of the Eocene sedimentary sequence (Ameki Formations) exposed in the Umuahia area and paleoclimate during that periods. The study area was mainly concentrated around Amaudara inUmuahia South and Ekeoha in Umuahia North. And the co-ordinate are as follows,location-1 0.5°30.80N, 0.7°26.93E, location-2 0.5°30.39N, 0.7°26.62E, location-3 0.5° 32.83N, 0.7°27.24 E and location-4 0.5°32.19 N, 0.7°26.13 E.
The aim of the study is to analyze the detailed sedimentary facies and describe the depositional environment in other to predict the depositional environment of the Eocene sediment (Ameki Formation) of the study area, which is underlain by rock unit of Ameki and predominately contains Laterite, mudstone, siltstone, claystone, sandstone and shale and Burrows were identified.
The rock sequence consist of reddish lateritic material, highly weathered mudstone capped with ripped bedded kaolinite clay unit, light grey claystone, cross-bedded sandstone with claystone, whitish sandstone, siltystone, fine-medium grained sandstone with pockets of mudclast capped with ferruginized ground and dark grey shale.
On the basis of gross lithology, sand-silt-clay percentage, color, texture and assemblage of sedimentary structure, eight distinct lithofacies type were recognized, grey shale facie (Gs), clay stone facie (Cs), cross-bedded sandstone facie (Cbs), mudstone facie (Mf), lateritic facie (Lf), mudstone facie (Bms), ferruginized sandstone facie (Fsf), sandstone facie (Bsf) are recognized within the lithosuccesion.
From the analysis, the facies are grouped into two facie association on the basis of grain size. The Fine-grained facies association (FFA) which consist of Gs, Cbs, Cs, Mf and Fst and the Medium to Fine-grained facies association (MFA) which also consist of Bms, Bsf and Lf. It also shows medium grained sand, moderately sorted to well sorted sandstone, Skewness ranged from symmetrical to positive skewed and kurtosis showed leptokurtic.
Deduction from facies analysis and grain size analysis shows that Ameki Formation consist of foraminifera and Mollusca which indicate that Ameki Formation was deposited in the estuarine(Marine) environment.
Friedman GM. Sorting coefficients and the long normality of the grain size distribution of clastic sandstones. Jour. Geol. 1962;70: 737-753.
Force FR. The provenance of rutile. J. Sediment. Petrol. 1980;50:485-488.
Friedman GM. Distinction between Dune, beach and river sand from their textural characteristics. Jour. Sed. Pet. 1961;31: 574-579.
Friedman GM, Sander. Principles of Sedimentology. 1978;76.
Nwajide CS. Eocene tidal sedimentation in the Anambra Basin, South- Eastern Nigeria. Sed. Geol. 1980;25:189-207.
Folk RL, Ward WC. Brazos River bar [Texas]; A study in the significance of grain size parameters. Journal of Sedimentary Research. 1957;27(1):3-26.
Miall AD. Architectural-element analysis: a new method of facies analysis applied to fluvial deposits. Earth-Science Reviews. 1985;22(4):261-308.
Harbaugh JW, Bonham-Carter G. Computer simulation in geology. Stanford Univ Calif; 1970.
Nwajide SC, et al. A geological field excursion guide to the Anambra Basin NAPE-UAP Mini Conference, Federal University of Technology Owerri, Imo State Nigeria. 2004;1-10.