TABLE OF CONTENTS
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
1.2 Aim and Objectives of the Study
1.3 Scope of the Study
1.4 Location of the Study Area
1.5 Physiographic and Climate
1.5.1 Climate
1.5.2 Relief
1.5.3 Vegetation
1.5.4 Drainage
1.6 Methods and
Materials
1.6.1 Field investigation
1.6.2 Outcrop mapping
1.6.3 Litholog Construction
CHAPTER TWO
REGIONAL GEOLOGY OF THE STUDY AREA
2.1 Regional Tectonic Setting and Structural
Framework
2.2 Regional Stratigraphic Setting and Basin
Fill
2.3 The Stratigraphic Fill of the Southern
Benue Trough
2.3.1 The Asu River Group
2.3.2 The Odukpani Formation
2.3.3 The Eze-Aku Group
2.3.4 The Awgu Shale
2.3.5 The
Nkporo Group
2.3.6 The Mamu
Formation
2.3.7 The
Ajali Formation
CHAPTER THREE
LITHOLOGIC
DESCRIPTION
3.1 Outcrop
Description
3.2 Unit A
3.2.1 Location 1
(behind Ibii Primary School)
3.2.2. Location 2 (Marlum Quarry Pit)
3.2.3 Location 3 (Crushed Stones Quarry Amasiri, the
Quarry Entrance)
3.2.4 Location
4 (Ozara-Ukwu shale)
3.2.5 Location
5 (Abandoned minning pit, 300m from
Amasiri junction)
3.3. Unit B
3.3.1 Location 6 (Road Cut near Macgregor Hill
along Amasiri-Afikpo Road)
3.3.2 Location 7 (Located At Ebonyi Hotels, Afikpo)
3.3.3 Location
8 (Ngodo-Mkpuma Hill)
3.4 UNIT C
3.4.1 Location 9 (Ibiam Girls Secondary School)
3.4.2 Location 10
(Road-cut along Owutu-Ogbu Road, Afikpo)
3.5. Unit D
3.5.1 Igneous intrusion
3.6 Outcrop Description
CHAPTER FOUR
THEORY OF GEO-ELECTRIC SURVEY AND METHOD OF
ANALYSIS
4.1 THEORITICAL BACKGROUND
4.1.1 Current
Flow and Equipotential Distribution
4.3 FUNDAMENTAL
ELECTRODE ARRANGEMENTS FOR CARRYING OUT
D.C RESISTIVITY SURVEYS
4.4 THE WENNER ARRAY
4.5 Resistivity of Earth Materials
4.6 True Resistivity
4.7 Automated dc Resistivity Profiling and Resistivity Imaging
4.8 The Materials for Geophysical Survey
4.9 Methods of the Geophysical
Survey
4.10 Precautions and problems
CHAPTER FIVE
RESULTS AND DISCULSION
5.1 Transverse 1
5.1 Transverse 2
5.3 Transverse 3
5.4 Transverse 4
CHAPTER FIVE
ECONOMIC GEOLOGY AND HYDROGEOLOGY
6.1 ECONOMIC GEOLOG
6.1.2 Dolerite
6.1.3 Kaoline
6.1.4 Limestone
6.1.5 Sandstone
6.1.6 Shale
6.1.7 Ironstone
6.1.8 Water
6.2 Hydrogeology
CHAPTER SEVEN
SUMMARY, CONCLUSION AND RECOMMENDATION
7.1 Summary
7.2 Conclusion
7.3 Recommendation
REFERENCES
APPENDIX: Traverse
1a, along Ai, Afikpo road, after timber shade. (100m)
APPENDIX I A: GEOPHYSICAL SURVEY SHEET Ozara-Ukwu Ridge
APPENDIX II A: GEOPHYSICAL SURVEY SHEET Before Ibii Junction
APPENDIX II B: GEOPHYSICAL
SURVEY SHEET along
Abakaliki-Afikpo road
APPENDIX III A: GEOPHYSICAL SURVEY SHEET Macgregor
APPENDIX III B: GEOPHYSICAL SURVEY SHEET Macgregor, along Abakaliki-Afikpo road
APPENDIX IV A: GEOPHYSICAL SURVEY SHEET After 1bii Junction
APPENDIX IV B: GEOPHYSICAL SURVEY SHEET: A Pathway After 1bii Junction
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
This work involved the observation, description of various
rock types and their field relationships. These rocks give information on the
general Geology of the area. Generally, a number of geophysical exploration
techniques are available which enable an insight to be obtained rapidly into
the nature of subsurface layers. These include geo-electric, electromagnetic,
seismic and geophysical borehole logging techniques. The choice of a particular
method is governed by the nature of the terrain and cost consideration. These
methods have been used extensively in groundwater investigation, geologic
mapping and engineering site investigation Etu-Efeotor and Akpokodje, 1990;
Obiakor and Chukwudebelu, 1992; Okwueze and Ezeanyim, 1985; Mbipom and
Archibong, 1989.
In geophysical investigations for lithological boundary,
ore prospecting, water exploration, depth to bedrock determinations, sand and
gravel exploration. The electrical resistivity method can be used to obtain
quickly and economically, details about the location, depth and resistivity of
subsurface formations, (Udoinyang, 1999). The basis of the electrical
resistivity method employs the measurement of electrical potential associated
with subsurface electrical current flow generated by a Direct Current (DC) or
slowly varying alternating current source (AC).
Factors that affect the measured potential include the presence and
quality of pore fluids and clays (Boyld, 1999).
Wiebeng, (1955) noted that the ratio of the current
applied, with a geometric factor K, which depend on the electrode separation
gives the quantity termed apparent resistivity. This study describes a direct
current geo-electric investigation for subsurface lithological boundary impacts
of Afikpo in Southern Benue Trough, Southeastern Nigeria. The aim of this investigation is to obtain
from the geophysical characteristics of the study area, a meaningful
delineation of the subsurface lithological boundary and other sedimentary
structures across different rock type for better understanding of the
subsurface geology of the study area.
1.2 Aim
and Objectives of the Study
The main objective of this research is to study the
lithologic characteristics of the Afikpo and it environ with a view to
delineate its lithological boundary using resistivity profiling.
1.3 Scope of the Study
(i)
Description of the
exposed outcrop sections of the study area.
(ii)
Mapping and
demarcation of the rocks encounter in to lithologic units.
(iii)
Determination of the
geo-electric sections at each profiling point in order to detect the change in
resistivity between different lithologies.
(iv)
Inferring of
geo-electric and geologic layers from the inverses resistivity plots.
(v)
To integrate the
results above to construct and digitize a geological map of the study area.
1.4 Location of the Study Area
The
study area is geographically located in southeastern Nigeria. The geographical limits
are defined by Latitude 5051’N and 5056’N and Longitude 7051’E
and 7056’E, and within part of the 1:25,000 Sheet 313 (Afikpo NE)
topographic map. It covers an area of about 60 km2(sixty square
kilometers). Major access roads into the
area are through the Abakaliki – Afikpo
Road, Okigwe – Afikpo Road, and Okposi – Amasiri – Afikpo Road, as
well as Cross River – Afikpo Road.
Good
network of roads link up such areas as Owutu Edda, Ibi, Amasiri, Amuro and
Afikpo which are the major towns in the study area. Figs. 1.1a and Fig.1.1b are
the location maps of the study area showing the access roads and major towns.
Fig. 1.1a: Map of Nigeria showing Ebonyi State
and location of the study area
Fig 1:1b Accessibility map of the study area.
1.5 Physiographic
and Climate
Physical features such as climate, relief, vegetation,
drainage pattern, soil and land use are observed in the study area.
1.5.1 Climate
The study area has two distinct seasons, a wet
season that lasts for eight months, and a dry season that lasts for four
months. The period from April to November form the rainy season while the
months of December to March are dry. The
months of December are cool and dusty because of harmattan while the period
from February to March is the hottest. The annual rainfall varies between
1500mm and 2000mm, with the driest month recording less than 300mm of rainfall
(Inyang, 1978; Obi, 2001). Relative
humidity in the study area is generally high and ranges between 60% and 95%
during the rainy season and fall below 60% during the dry season (Monanu, 1978;
Nimako, 2008). Fig. 1.2 is the climatic map showing the average rainfall of
study area.
Fig. 1.2: Map Southern Nigerian showing
Climatic condition with respect to the annual rainfall of the study area
(Inyang, 1978).
1.5.2 Relief
The area consists of gently undulating lowlands
with alternating sandstone ridges and shaly swales (Fig. 1.3). The average elevation of the study area is
about 100m above sea level. Elevation
within the sandstone ridges could however be up to 120m above sea level. The
outcropping rocks differ in their resistance to weathering/erosion. The
erosional patterns are therefore controlled by the lithology as well as the
structure of the rocks.
Fig. 1.3: Vegetation and topography
map of the study Area. The photograph (Fig.1.3) was taken at Ozara-Ukwu ridge, Afikpo.
The picture was taken on the peak of the ridge. Elevation is 210 ft. above sea
level, while GPS Coordinates are 05o 54/N, 07o56/E.
1.5.3 Vegetation
According to Ilorje (1978), the study area belongs to the
Guinea Savannah type of vegetation, which could further be classified as a park
land Savannah
which occur as a result of long period of free devastation by man and fire, Igbozuluike
(1975), described the vegetation of the area as rain forest type (Fig. 1.4).
Fig. 1.4: Vegetation of the
Study Area (Modified after Igbozuluike, 1975).
1.5.4 Drainage
The study area falls within the Cross River
drainage basin. The river systems that drain the study area include the Iyioha River,
the Otoni River,
the Elummahi River,
the Iyiokwu and the Cross
River, with their
tributaries. These rivers empty into the
Cross River drainage system east of the study
area. The drainage pattern varies from
dendritic to trellis. Fig. 1.5 is the
drainage map of the study area.
Fig. 1.5: Drainage
map of the study area.
1.6 Methods and
Materials
This study was carried out in three phases as
follows;
i.
Field investigation.
ii.
Geophysical techniques
iii.
Interpretation
1.6.1 Field
investigation
This
involves field mapping and lithologic logging of outcrop sections to provide
data for lithofacies and paleoenvironmental interpretation. Outcrops were studied lithologically with
their attributes and characteristics recorded with representative samples taken
in places.
Sample locations and elevations were obtained
using Global Positioning System (GPS).
Sketches of lithologic logs of notable outcrop
sections were produced.
The attitudes of the beds and other structures
were measured using the Rangers Compass.
Collected samples were appropriately packaged,
labeled and sealed in sample bags.
Instruments and materials used include:
a.
The Sheet 313 (Afikpo NE
topographic map) covering the study area
b.
Measuring tapes and
rulers
c.
Rangers compass
d.
Digital camera
e.
Hand lens
f.
Geologic hammer
g.
Ranging poles, and
h.
Sample bags
i.
Dilute Hydrochloric
Acid (HCl).
1.6.2 Outcrop mapping
The mapping was carried out using 1:25,000 Afikpo NE
(Sheet 313) topographic map as base map.
Several outcrop sections of the sandstone were studied and logged. The lithologic and sediment logic
characteristics of the outcrop sections were captured using a logging format
designed to provide an insight into the vertical variation in lithology,
texture (grain size, sorting, roundedness), sedimentary structures, fossil
content, bed thickness, and contact types.
The lithologic logs were described in details for each outcrop
studied. The outcrop locations (co-ordinates)
were geo-referenced and elevation above sea level recorded using the Global
Positioning System (GPS).
Representative samples were taken from all the
logged sections for laboratory processing and more detailed textural and
compositional analysis. Structural
features such as dips and strikes of beds, faults and joints/fractures
orientations were measured and described.
Photographs and sketches of important sedimentary and structural
features were also taken.
The mapping was done by examining and
describing the outcrops in detail. The
mapping exercise was done using the simple traverse and compass method. The various rock types were delineated using
exposed contacts where they are available and by inferences using topography,
soil type and vegetation. Unconformable
contacts were mapped using high discordance in dips of lithologic units.
1.6.3 Litholog Construction
The construction of lithologic log of vertical
sequences of important sedimentological features is a good way of interpreting
depositional systems and environments of deposition for an outcrop (Visher,
1965; Zervaset al., 2009). A table
containing important sedimentological characteristics was prepared for each of
the logged sections. The tables with the
sketches were used to construct digitized versions of lithologic logs. The
important sedimentological parameters used in the litholog constructions
include bed thickness, lithology, percentage lithology, type of basal contacts
(gradational, sharp, or erosional), grain size at the base, grain size at the
top, type and intensity of bioturbation, physical sedimentary structures,
fossil contents as well as other stratigraphic information. These parameters
are the key inputs for creating sedimentary logs in SEDLOGTM
software. Sedlog is a multi – platform intuitive graphical user interface software package for creating
graphic sediment logs (Zervaset al.,
2009).
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