Extent and Distribution of Groundwater Resources in Parts of Anambra State, Southeastern, Nigeria

The extent and distribution of groundwater resources in parts of Anambra State, Nigeria has been investigated. The results show that the study area is directly underlain by four different geological formations including, Alluvial Plain Sands, Ogwashi-Asaba Formation, Ameki/Nanka Sands and Imo Shale, with varying water storage and yielding capacities. Borehole depths within the Alluvial Plain Sands are shallow (5-30m) yet the sands are excellent aquifers with high yields (3-5 litres/sec) especially along the Anambra West – Onitsha -Ogbaru L.G.A. axis. Elsewhere the yield is low (about 0.5litres/sec) and may dry up at peak dry season periods. The Ogwashi-Asaba Formation occurs in a north-southerly trend and underlies Ekwusigo, Nnewi North and South and Ihiala Local Government Areas. This formation consists of multiple aquifers and a depth to water table ranging from 50 to 110m. Within it, transmissivity values of 37.54 to 95.5m2/day and a yield of up to 5litres/sec were recorded. The Ameki/Nanka Sands is a prolific water producer and underlies Aguata, Anaocha, Njikoka,Dunukofia, Oyi and Anambra East Local Government Areas. Four aquifer horizons were identified within this formation, designated; shallow, upper, middle and deep aquifers. The most exploited are the upper and middle aquifers, while the least, but most prolific is the deep aquifer with an average yield of 5litres/sec. Imo Shale, because of its sedimentological nature is a poor aquifer. The gravelly intercalations within this formation are usually too thin to sustain continuous water pumping. This study indicates that the extent and distribution ofgroundwater within the study area is controlled predominantly by lithology and other secondary factors including topography and nearness to source of recharge

Carbonate microfacies and major element content of the Paleocene – Eocene sections exposed at the Sagamu quarry, eastern Dahomey basin, Nigeria.

The Paleocene-Eocene limestone and shale units exposed at the Sagamu quarry, southwestern Nigeria, were investigated for the carbonate microfacies and major geochemical elements to deduce the depositional environment and the diagenetic history of the limestone. From field observations the limestone is generally massive to wavy laminated, yellowish brown to light grey and fossiliferous. The shales are light to dark grey, fissile, clayey and concretionary. Based on the microfacies studies, the limestone include: sandy bioclastic packstone, biomicritic mudstone,biomicritic wackestone, biosparitic grainstone, biomicrtic packstone and oolitic packstone-grainstone. Gastropods, peleycpods, foraminifera, ostracodes and algae constitute the major bioclasts while pellets and lithoclasts are the major non-bioclastic components of the lithofacies.Geochemically, the limestone is rich in CaO (46.82%), SiO2 (5.72%) and MgO (1.97%). The values indicate non-dolomitic limestone. The CaO and MgO contents are however lower at the base than at the top of the limestone and probably reflects the sandy nature of this part. Ternary plot shows that the limestone is richly calcitic. The shales are rich in SiO2 (44.43%), Al3O2 (15.90%) and Fe2O3 (7.68%). The high values of CaO (6.35%) and MgO (2.62%) make them calcareous shales. The lithologic, paleontologic and petrographic data indicate deposition of the units in a shallow marine shelflagoon environment, formed during the Maastrichtian sea flooding into Dahomey Basin. The porosity and permeability of the limestones are generally low while fracturing and dissolution improved the permeability, the effect of late diagenesis reduced it significantly