The Abakaliki metropolis is
geologically, underlain by the Abakaliki Shale Formation of the Asu River Group . The Asu River Group sediments are predominantly shales, and
localized occurrences of sandstone, siltstone and limestone intercalations. It was generally believed to have started depositing
in the mid-Albian period and was deposited within the lower (or southern) Benue
Trough, southeastern Nigeria.
The geology of the Abakaliki metropolis is shown in our previous post Emplaced in these Asu River Group sediments are intermediates to basic intrusive, extrusives and pyroclastics. The group has average thickness of about 2000m and rests unconformably on the Precambrian Basement. The Abakaliki Shale Formation, which has an average thickness of about 500 m, is dominantly shale, dark grey in colour, blocky, and non-micaceous in most locations. It is calcareous (calcite-cemented) and deeply weathered to brownish clay in the greater part of the formation.
The geology of the Abakaliki metropolis is shown in our previous post Emplaced in these Asu River Group sediments are intermediates to basic intrusive, extrusives and pyroclastics. The group has average thickness of about 2000m and rests unconformably on the Precambrian Basement. The Abakaliki Shale Formation, which has an average thickness of about 500 m, is dominantly shale, dark grey in colour, blocky, and non-micaceous in most locations. It is calcareous (calcite-cemented) and deeply weathered to brownish clay in the greater part of the formation.
Aghamelu
et al. (2011) note that the major part of the Abakaliki metropolis is underlain
by aquiclude; except in locations or zones where secondary aquiferous conditions
were made possible by syn- and post depositional circumstances. The syn-depositional
circumstance is the occurrence of lenses of sandstone or siltstone beds, while
the post depositional circumstances include weathering, fracturing or shearing,
and volcanic intrusions. The zones are recharged mostly in the peak of rainy
season and by surface waters in the area. The major river that drains the area
is the Ebonyi River and its tributaries; Udene and Iyiokwu Rivers. Both
tributaries are perennial and usually overflow their banks at the peak of the
rains.