PROCEEDINGS, Thirty-Second Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 22-24, 2007 SGP-TR-183 LITHOSTRATIGRAPHY OF NIGERIA-AN OVERVIEW Kazeem Akorede Shitta Kamad Petroleum Limited 28 New Ilesha/Akure Road, Gbangan,Osun State,234,Nigeria e-mail: [email protected] The world’s water resources include the ABSTRACT entire range of natural waters on earth, either in vapour, liquid or solid form. Water is classified as Nigeria lies very close to the equator (hot country) surface water or groundwater. Surface water include North eastern Africa between latitude 4 N and 14 N rain water collected into rivers, lakes, reservoirs and and longitude 5 E and 12 E. The country is located at oceans while groundwater include natural springs, the Northern end of Eastern branch of east Africa rift well and boreholes. system. Groundwater is commonly understood as Nigeria geological set up comprises broadly water occupying the voids within a geologic stratum, sedimentary formation and crystalline basement groundwater is free from suspend matter and complex, which occur more or less in equal bacteria. It can be said to be pure, clear and proportion all over the country. The sediment is colourless. Groundwater has greater quality than mainly Upper Cretaceous to recent in age while the surface water. basement complex rocks are thought to be About 495,000 children die annually of Precambrian. various diseases due to drinking of water that are not The studied area lies between latitude 12.4" and properly safe and sanitize (sea, stream e.t.c.), even as 11.11"W and longitude 13.81" and 14.13" S. The population increases and industries required all over studied area is underlain by Precambrian basement the world, most people generally required about 2.5 complex of southern western Nigeria .The major rock litres of water everyday for direct consumption. The in the area is charnokite and granite rock. The granite average amount of water used domestically each day rock which are member of the older granite suite by every person is about 190 litres (Hamill and Bell, occupy about 65% of the total area .The principal 1986). granite is petrographic variety are recognized .The Generally, industries require approximately fine grained biotite-granite medium-coarse, non one quarter to one third of the public water supply porphyritic biotite -hornblende granite and coarse - under normal condition the easiest and most porphyritic biotite -hornblende granite. Also three convenient way to meet the public demand for water main textural type of charnokitic rock are also is to utilize surface water resources, but distinguished are coarse grained, massive fine unfortunately, water such as river, lake, stream e.t.c. grained and gneissic fine grained .The mode of are less plentiful than can be imagined. It can be occurrence of rock is three (1) core of the granite recorded that surface water resources account for less rock as exemplified by study area and few smaller than 2 percent of the world’s fresh water. bodies (2) Margin of the granite bodies as seen in The latter fresh water available however is Ijare and Uro edemo-idemo Charnokitic bodies and unevenly distributed while the sources that are (3) Discrete bodies of the gneissic fine grained available have been either contaminated or polluted. charnokitic rock within the country gneisses as seen (Hamill and Bell, 1986). in Ilaro and Iju and Emirin village. All the charnokite Groundwater accounts for about 98 percent in the region are dark-greenish to greenish-gray rocks of the world’s fresh water and is fairly evenly with bluish quartz and greenish feldspar. distributed throughout the world. It provides a reasonable constant supply which is not completely susceptible to drying up under natural condition INTRODUCTION unlike surface water (World water balance and water Water is known to be a universal solvent. It resources of the earth UNECO Copyright 1978). is also one of the natural resources tapped by man, All over the globe, groundwater has been a animals and plants to meet their needs for life very good and important source of water supply. It sustenance. has been of continuous and tremendous use in irrigation industries and urban centers, as well as in rural communities. It is conveniently available at result obtained geoelectric sections point of use and possesses excellent quality that were generated. requires little or no treatment in most cases. IV. Interpretation of Results: Result obtained from each VES station were OCCURRENCE OF GROUND WATER completed and interpreted in order to The concept which explains the ultimate destination determine the best location for of rainwater is the sea either directly through run off groundwater development in the study. or indirectly be infiltration and subsurface flow. A system of water movement in the atmosphere or GEOLOGY OF THE STUDY AREA rainfall, dews, hailstones or snowfalls over land as Akure south Local Government falls within the run off. Vertical and horizontal movement basement complex region of Nigeria. The studied underground as infiltration or subsurface and area lies between latitude 12 o 04 o and 11 o 11 o W continuous movement of all forms of water is the and 13 o 81 o and 14o13 o. and is underlain by hydrogeology cycle. In the atmosphere, water precambian basement complex rocks of South vapours condense and may give rise to precipitation. Western Nigeria. However, not all this precipitation will reach the Several part of Africa is underlain by ground surface; some are intercepted by vegetation crystalline basement complex rocks. The major types cover or surface of building and other structures and of rocks in Akure are granite rocks and charnokite. then evaporate back into the atmosphere. The granite rocks which are member of the The precipitation that reaches the ground older granite suit occupy about 65% of the total area surface may flow in to stream, lake and ocean, where of Akure. Three principal petrographic varieties are it will either be evaporated or form seepages recognized, the fine-grained biotite granite, medium intruding in to the ground likewise soil moisture and to coarse grained, non-porphyritic biotite – further percolate downward to underline aquifer hornblende granite and coarse – porphyritic biotite- where it may be held for several years longer. hornblade granite. Groundwater in Nigeria is restricted by the The classification is based largely on the fact that more than half of the country is underlain by textural characteristics. Also three main textural types crystalline basement rock of pre-cambian era. of charnockitic rocks are also distinguished in Akure. The main rock types in this geological These are the coarse-grained variety, terrain include igneous and metamorphic rock such as massive fine grained and the gneissic fine-grained migmatites and granite gneisses. types. Unlike most of the older granite, the Generally in their unaltered form, they are charnokite rocks do not occur in form of smooth characterized by low porosity and permeability. rounded boulders and only a few low hills all forming Porosity in basement rocks is by induction through oval to sub-circular and elongated bodies. weathering while secondary permeability induces by The charnockitic rocks appear to have three tectonic activities which manifest in form of that modes of occurrence in the area, the first occurrence often act as conduct path facilitating water is within what seems to be the ‘core’ of the granite movement. rock as exemplified by Akure body and few smaller In other words, aquiferous zones in the bodies. basement terrain include fractured/weathered rocks. The second is along the margins of the The yielding capacity of well, drilled within such granite bodies as seem in Ijare and Uro Edemo- rock are always very enormous. Idemo charnockitic bodies. The first two modes of occurrence are mainly shown by the coarse-grained RESEARCH METHODOLOGY. charnockitic variety. The last mode of occurrence is I. Literature Review: All available represented by the discrete bodies of the gneissic geological/hydrological information fine-grained charnockitic rocks within the country were collected through the reading of gneisses as seen in Ilara and also near Iju and Emirin journal, reference seminar paper villages. (Olorunfemi M.O., 1990) All the charnockitic in the region are dark- II. Data Gathering: All vertical electrical greenish to greenish-gray rocks with bluish quartz are sounding data were collected from greenish feldspars (V. O. Olarewaju, 1997). water section of the Federal Ministry of Agriculture and Water Resources HYDROGEOLOGY OF THE STUDY AREA Abuja, Wenner array was used in The major river in Akure in Ondo State is collecting the date. Ero River,this river originates from Igbara Oke road, III. Data Analysis: The data were about 16-18km distance to Akure town. interpreted by using partial curve Osun River is the major source of water matching technique. Computer was then runoff in Akure town, there are other smaller rivers used to interpret the results, from the such as Owuruwu River which is about 60m distance from Apex Nursery and Primary School, Oba Adesida, which is the Ves location. This river flows layer thickness varying from 17.5m – 29m with to meet Osun River at Akure road, the other rivers resistivity value ranging between 90ohms-m to such as Otenre River, Omi Atamo, are smaller rivers 240ohms-m. The layer will be good for groundwater that serve as runoff in the town; they meet Osun accommodation if the fractures are interconnected River at a point known as Osun Amon.Osun River and permeable. flows from the Eastern part to Western part of the The fresh basement which is the fourth layer town and then flows to Ise town to meet a bigger is characterized by high resistivity value up to river called Ogbese in Ondo State.