The Abakaliki shale formation underlies the study area. The shale
formation belongs to the Asu-River group of the Albian Cretaceous sediments.
The Aus-River group is middle Albian sediment and consists of very thick
marine, dark, grey shales and minor limestones. The sediment consists of poorly
bedded sand shales known as Abakaliki shales with sandstone and sandy limestone
lenses. (Kogbe, 1976). From field observation,
the rocks of the study area consist of variably coloured shales and mudstones,
baked shale as well as ironstone along the veins.
The baked shales
are concentrated at Onu-Ebonyi. The ironstone occur as interbeds within the
shales as vein fillings. The shales range at depth to dark greyish and reddish
brown up the sequence.
