INTEGRATION OF ELECTRICAL RESISTIVITY AND INDUCED POLARIZATION FOR SUBSURFACE IMAGING AROUND IHE POND, NSUKKA, ANAMBRA BASIN

ABSTRACT

Integration of 2D geophysical methods, Electrical Resistivity Imaging (ERI) and Induced Polarization (IP) were used to study the subsurface geology and structures around Ihe pond, Nsukka in Anambra basin. The research work has delineated the geologic structures and strata responsible for the water in the pond, and determined the origin of the Pond. Three 2D resisitivity profiles of maximum spread lengths of 500, 400 and 500m were run around the pond. Horizontal profiling, using Wenner array configuration was employed in the data acquisition for both methods. Four faults designated Apo 1, 2, 3 and 4 with colour codes, blue, red, green and black and their fault zones were mapped. The faults were located at points 224, 265 and 325m on ER model line one, and at points 170, 205, 275 and 296m on ER model line two. Three lithologic units of consolidated coarse, medium grained, fine-grained sandstones and saturated zones were identified on the ER and IP Psuedosections. The ER and IP values from the three profiles range from 136 - 21559Wm and -81.0 to 240Ms respectively. The faults zone acts as water pathway to the pond. Inverse chargeability models established the faults zones, as large gradients of chargeability. Correlation of strata to known formation depicts the presence of consolidated coarse to medium grained sandstones, while known exposed fault was correlated to Apo 3 fault using coordinates readings. Analysed sample of water from the pond shows low Salinity and sulfides. Soil sample oxide content was also analysed to compliment the geology, and the result shows that Aluminum oxide (Al203), Silicon oxide (Si02), Ferrous oxide (Fe203), Zinc oxide (Zn0) and Sodium oxide (Na203) are relatively low and are in conformity with characteristics of laterite.

TABLE OF CONTENTS

CONTENTS    PAGES

TITLE PAGE----------i

CERTIFICATION---------ii

DEDICATION---------iii

ACKNOWLEDGEMENT--------iv

TABLE OF CONTENTS--------v

LIST OF FIGURES---------x

LIST OF TABLE--------xii

ABSTRACT----------xiii

CHAPTER ONE

1.1Introduction--------- 1

1.2Study Location--------2

1.3Physiography--------3

1.4Aims and Objectives -------6

1.5Literature Review--------6

1.6Methodology--------9

1.7Data Gathering--------9

CHAPTER TWO

2.0General Geology of Anambra Basin-----11

2.1Introduction--------11

2.2Geological Setting of Anambra Basin-----13

2.3Sedimentology--------15

2.4Regional Stratigraphic Sequence------17

2.5Tectonic Setting and Geologic Evolution-----19

CHAPTER THREE

3.0Basic concepts of  Electrical Resistivity and Induced Polarization  --24

3.1Introduction to Resistivity Method-----24

3.2Electrical Properties of Rocks------25

3.3The Relationship Between Geology and Resistivi ----29

3.4Basic Theory of Electrical Resisitivity Method----32

3.4.1Apparent Resistivity  --------35

3.5Electrode Arrays--------36

3.5.1Schlumberger Array - -- -----37

3.5.2Wenner Array ---------39

3.5.3Dipole – Dipole Array ---------41

3.6Uses, Advantages and Disadvantages of ER Technique ---43

3.6.1Uses of Electrical Resistivity------43

3.6.2Advantages of Electrical Resistivity Technique---43

3.6.3Disadvantages of Electrical Resistivity Technique---44

3.7Introduction  to Induced Polarization - ----44

3.8Sources of Induced Polarization Effects-----45

3.8.1Membrane Polarization-------45

3.8.2Electrode Polarization-------47

3.9Induced Polarization Measurement-----50

3.9.1Introduction--------50

3.9.2Time Domain Measurement------50

3.9.3Frequency Domain IP Measurement-----54

3.10Relative Phase Shift and Phase Components----57

3.11Induced Polarization Response-------59

CHAPTER FOUR

4.0Materials and Methods-------65

4.1Materials---------65

4.1.1Terrameter SAS/1000-------65

4.1.2Electrodes---------68

4.1.3Cables---------68

4.1.4Hammer---------68

4.1.5Battery---------69

4.1.6Global positioning system-------69

4.1.7Rope and Measuring Tape-------69

4.1.8Cutlass---------69

4.1.9Phones---------69

4.2Methods---------71

4.2.1Introduction---------71

4.2.2Horizontal profiling (Wenner Array)-----71

4.3Data Acquisition--------72

4.4Data Processing--------72

4.5Data Interpretation--------73

4.5.1Fault Description--------73

4.5.2Mapping of Strata--------76

4.6Geologic Resources and laboratory analysis----76

4.6.1Laterite---------76

4.6.2Sandstone---------78

4.6.3Clay----------78

4.6.4Coal----------78

4.6.5Hydrogeology--------79

4.6.6Water---------80

CHAPTER FIVE

5.0Data presentation and discussion of Results----82

5.1Introduction--------82

5.2Discussion of Faults and Strata on figure 5.1A----82

5.2.1Faults---------82

5.2.2Strata84

5.3Discussion of Fault Zones/Strata on Figure 5.1B----84

5.3.1Faults Zones---------84

5.3.2Strata---------84

5.4Discussion of Faults/Strata on Figure 5.2A-----85

5.4.1Faults---------85

5.4.2Strata---------85

5.5Discussion of Fault zone/Strata on Figure 5.2B----87

5.5.1Fault Zones---------87

5.5.2Strata---------87

5.6Discussion of Strata on Figure 5.3A------87

5.7        Discussion of Strata on Figure 5.3B------89

5.8Known Formation--------89

5.9Correlation of Strata to Known Formation-----92

5.10Correlation of fault to Known Fault-----92

5.11Water Sampling Results-------95

5.12Soil Sampling Results-------95

CHAPTER SIX

8.0Conclusions and Recommendations------97

8.1Conclusions---------97

8.2Recommendations--------99 

References----------100

Appendix 1----------106

Appendix 2----------107

Appendix 3----------108

Appendix 4----------109

Appendix 5----------110

Appendix 6----------111

Appendix 7----------113

Appendix 8----------115

LIST OF FIGURES

Figure 1.1: Map of Nigeria showing the location of study area---4

Figure 1.2: Base map of the Study Area, showing Ihe Pond, accessibility and the

 three profiles--------5

Figure 1.3: Summary of stratigraphic data on the Palaeogene sucession in

                  Southeastern Nigeria-------10

Figure 2.1: Geologic map of Southern Nigeria showing Anambra Basin--12

Figure 2.2:  Map of Benue Trough and Related Athlantic Fracture Zone--14

Figure 2.3: The Sedimentary and Stratigraphy of the Anambra Basin, Lower

 Benue Trough and Afikpo Basin-----16

Figure 2.4: Correlation Chart for Early Cretaceous-Tertiary Strata in 

Southern Nigeria -------21

Figure 2.5: Tectonic map of southern Nigeria-----22

Figure 3.1: Principle of Ohm’s law-------26

Figure 3.2:  Equipotentials and Current lines for a pair of current Electrodes

                    A and B on a Homogeneous half-space ----34

Figure 3.3:  Schlumberger Array-------38

Figure 3.4:  Wenner Array--------40

Figure 3.5: Dipole – Dipole Array-------42

Figure 3.6:  Electrolytic flow in upper pore, electrode polarization in the lower pore49

Figure 3.7: Time Domain IP Waveform  ------52

Figure 3.8: Different Measures of  Time-Domain IP effect. (a) Comparison of V(t), with  

                   V (b)     Integral of V(t) over a Time Interval ----53

Figure 3.9:   Frequency Domain IP Waveform  ------55

Figure 3.10: Equipotential electrical Circuit to Simulate the effect---56

Figure 3.11: Phase Shift Diagram -------59

Figure 4.1: Photograph Showing  SAS/1000, Four Reels of wire, Battery, Tape

                   and Electrode during data Acquisition-----67

Figure 4.2: Global Positioning System (GPS)-----70

Figure 4.3: Base-Map showing the Interpreted Faults across profile 

one and two--------75

Figure 5.1A:  Inverse Resistivity Model of Line one----83

Figure 5.1B: Inverse Chargeability Model of Line one----83

Figure 5.2A:  Inverse Resistivity Model of Line two----86

Figure 5.2B: Inverse Chargeability Model of Line two----86

Figure 5.3A:   Inverse Resistivity model of Line three----88

Figure 5.3B Inverse Chargeability Model of Line three----88

Figure 5.4: Study Outcrop around Ihe Pond in Nsukka Formation--90

Figure 5.5:  Correlation of Strata to Known Formation----91

Figure 5.6:  Correlation of Fault to Known fault-----93

Figure 5.7:  The Extension of the Known fault (Downthrown)---94

LIST OF TABLES

Table 3.1: Resistivities of some common Rocks, Minerals, and Chemicals  --31

Table 3.2: Chargeability of Different Minerals-----61

Table 3.3: Chargeability of Various Minerals and Rocks----62

Table 3.4: Chargeability of various Materials----64

Table 5.1:  Water Sampling Results   ------95

Table 5.2: Soil Sampling Results  -------96