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Vol.2 , No. 6, Publication Date: Oct. 8, 2015, Page: 274-282
| [1] | E. O. Igwe, Department of Geology, Ebonyi State University, Abakaliki, Nigeria. |
| [2] | A. U. Okoro, Department of Geological Sciences, NnamdiAzikiwe University, Awka, Nigeria. |
| [3] | A. I. Obasi, Department of Geology, Ebonyi State University, Abakaliki, Nigeria. |
The Eze-Aku Shale represents the basal unit of the Eze-Aku Group and unconformably overlies the Asu River Group in the Afikpo Synclinorium. Foramineferal biostratigraphic analysis of the shale facies was carried out to re-evaluate the age, paleoecology and paleoenvironment of the shale unit. Field studies show that the shales are flaggy, dark grey to black, calcareous, thinly laminated with pelecypod moulds, gypsum efflouresence between the laminae and mudstone interbeds. The biostratigraphic study shows that the shales contain both planktonic and benthonic foraminiferal assemblages. The planktonic forms include species of Hedbergellids, Heterohellicids, Whitenella and Archeogloberina blowi. Benthonic forms are mainly species of Ammobaculites, Haplophragmoides, Lenticulina, Gavelinella, Globigerinelloides. Late Cenomanian to Turonian age was assigned to the Eze-Aku Shale facies based on the planktonic foraminiferal assemblages of Hedbergellids and Heterohellicids. The foraminiferal assemblages suggest middle neritic to deeper water, normal salinity environment with prevailing anoxic conditions. This explains the paucity of biofacies and mixture of both shallow and deep water microfauna were attributed to mass mortalities due to reduced salinities, anoxic/successive deepening of the depositional environmental setting.
Keywords
Eze-Aku Shale, Foraminiferal Assemblages, Afikpo Synclinorium
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