AQUIFER POTENTIALS OF THE CAMPANO ? MAASTRICHTIAN GOMBE SANDSTONE, GONGOLA BASIN, UPPER BENUE TROUGH, NORTH EASTERN NIGERIA

The Campano ? Maastrichtian Gombe Sandstone occurs as a relatively linear strip of an outcrop, striking northeast?southwest adjacent to the Kerri Kerri plateau in the Gongola Basin. This formation is of deltaic origin and has attained a thickness of over 340 meters. Its arenaceous content is about 80%, therefore, it may constitute a very important aquifer for the underground water system in Gombe town and adjacent areas. The aquifer properties of the Gombe Sandstone were evaluated based on petrographic studies, permeameter analysis and bivariate plot relationship of standard deviation versus mean. The average values of porosities obtained from these analyses for this formation standout at 15%, 23% and 33% respectively. While permeability varied from 100?200mD in permeameter analysis and 10 ? 1400mD in bivariate plot of standard deviation versus mean. Notwithstanding the relatively good porosity and permeability values for this formation, the yields observed from boreholes are relatively low in Gombe town, usually ranging from 1.4 ? 2.8 litres per second. However, in the west and northwest, especially around Kwadon village, the yield appreciably improves to 4.8 ? 5.6 litres per second. The larger part of the Gombe Sandstone in the Gombe area is generally uplifted, while at Kwadon village in the western part of the basin, its greater thickness occurs in the subsurface. Considering the fact that the Gombe Sandstone was formed in a deltaic environment, the upper part defined by delta front sand which have been observed from outcrop studies to consist of good porosity and permeability are usually uplifted in the Gombe area. This makes the moderate ? poorly sorted delta slope sand of the lower part of the Gombe Sandstone as the dominantly possible aquifer for underground water, hence, the poor yield. However, in the Kwadon area, the greater thickness of the well sorted delta front sands are well preserved in the subsurface, and this led to the generation of a high yield which is further supported by the drainage pattern of the basin, which directs flow towards the Kwadon area in the west.