Thesis Abstract

Abstract
The use of resistivity methods for detecting horizontal and vertical discontinuities in the electrical properties of the ground has been a valuable tool in groundwater exploration and environmental studies. This research abstract focuses on the application of resistivity methods in identifying subsurface features such as faults, fractures, and various geological structures that influence the movement and storage of groundwater. Horizontal discontinuities, such as faults and fractures, can significantly impact groundwater flow and storage. By conducting resistivity surveys, variations in subsurface electrical properties can be correlated with the presence of these features. Differentiating between materials with varying resistivity values allows for the mapping of subsurface structures that can act as barriers or conduits for groundwater flow. Vertical discontinuities, such as changes in lithology or the presence of aquifers and aquitards, also play a crucial role in groundwater detection and characterization. Resistivity methods can be used to delineate these vertical changes in the subsurface by measuring the electrical resistivity of different layers. This information is vital for understanding the groundwater system's complexity and identifying potential zones for water extraction or contamination vulnerability. The choice of resistivity method (e.g., electrical resistivity tomography, vertical electrical sounding) depends on the specific objectives of the groundwater investigation and the geological setting. For instance, vertical electrical sounding is suitable for determining the depth to the water table and delineating different aquifer layers, while electrical resistivity tomography is effective for imaging horizontal structures like faults and fractures. Interpreting resistivity data requires integrating geological information with the electrical properties of the subsurface materials. In complex geological settings, the presence of both horizontal and vertical discontinuities can create challenges in accurately characterizing groundwater resources. However, advances in data processing techniques, inversion algorithms, and modeling tools have improved the resolution and accuracy of resistivity surveys in detecting subsurface features. Overall, the application of resistivity methods in groundwater detection offers valuable insights into the subsurface's electrical properties, enabling the identification of horizontal and vertical discontinuities that influence groundwater flow and storage. By combining geophysical surveys with geological knowledge, researchers and environmental professionals can enhance their understanding of groundwater systems and make informed decisions regarding resource management and environmental protection.

Thesis Overview

 Introduction

The resistivity method is used in the study of the horizontal and vertical discontinuities in the electrical properties of the ground and also in the detection of three dimensional bodies of anomalous electrical conductivity. In the study of ground water movement in obubra area, the the resistivity method commonly employed are the electrical resistivity method. Electrical resistivity method is one of the most useful techniques in groundwater geophysical exploration, because the resistivity of rocks is sensitive to its ionic content (Alile, et al., 2011). The method allows a quantitative result to be obtained by using a controlled source of specific dimensions. Records show that the depths of aquifers differ from place to place because of variation in geo-thermal and geo-structural occurrence (Okwueze, 1996). Therefore, the need to study the area for groundwater potential especially in terms of determining the flow direction is a prerequisite for portable ground water exploration and exploitation in this area.

1.1      Location And Geology Of The Area

The study area lies between latitudes 50 15′ and 60 15′N and longitudes 70 45′ and 80 45′E. It is located within the sub-equatorial climatic region of Nigeria with a total annual rainfall of more than 300 to 400cm. Temperature ranged from 250C to 280C. The area experiences two seasons, these are the wet season which lasts from April to September with a peak in June and July while the dry seasons lasts from October to March (Iloeje,1991).

 The study area is underlain by two major lithologic units: Crystalline basement and Cretaceous sediments. The crystalline basement rocks occupy the extreme south of the study area. Also, there are intermediate rocks scatteredin patches around Obubra, Iyamayong, Iyamitet, Ikom, Nkpani and Usumutong. The Cretaceous sediments cover about 90% of the study area. Asu River Group is the basal and oldest recorded sediment in the study area. It is dominated by bluish gray/black to olivine brown shale and sandy shale, fine – grained micaceouscalcareous sandstone and siltstone with limestone lenses. The shale is often carbonaceous and pyritic which indicates that the sediments were deposited under a poorly oxygenated shallow water environment of restricted circulation, an indication of low energy environment (Petters et al., 1987). In general, Southern Obubra lies within the Cross River plain and the clastic beds in the study area can be ascribed to the Ezillo Formation. The Ezillo Formation comprises mostly dark gray shales with fine sandstone and siltstone intercalations in the lower part, and an upper unit that is highly bioturbated, fine medium sandstone, similar to the sandstone of the Amaseri Formation. The Ezillo Formation between Appiapum and Ikom was deposited in a deltaic coastal plain, in brackish marshes and inter-distributary bays (Barth, et al., 1995). A major river (Cross River) exists in the study area into which minor streams empty their loads. The elevation of the study area ranged from 14 to 170m above sea level. The relief is characterized by undulations running at undefined direction and variably demarcating the very lowland areas from moderate relief landmarks. The occurrence of the low plains is occasionally broken by inselbergs of granite and basalts in the southern portion of the study area. In the sediment filled portions, the low plains are occasionally broken by flat -topped hills of sandstone ridges and igneous intrusive with highly ferroginized sandstones with gravels resulting from uplifts. The area is drained by the Cross River with major tributaries like, Udip, Ukong, Lakpoi, Okwo, and Okpon rivers. These rivers form a network of dendritic drainage system