determination of subsurface delineation using electrical...

Physics Journal

Vol. 1, No. 2, 2015, pp. 97-104

http://www.aiscience.org/journal/pj

* Corresponding author

E-mail address: [email protected] (A. T. Olugbenga)

Determination of Subsurface Delineation Using Electrical Resistivity Sounding in Zuba and Environs of Gwagwalada Area Council, Abuja, North Central, Nigeria

Adeeko Tajudeen Olugbenga1, *, Ojo Emmanuel Osiewundo2

1Department of Physics, Faculty of Science, University of Abuja, Abuja, Nigeria

2Science Infrastructure Department, National Agency for Science and Engineering Infrastructure, Abuja, Nigeria

Abstract

The electrical resistivity investigation of Zuba and Tungamaje area, of Gwagwalada Area Council, Abuja, was carried out with

a view to providing geology and geophysical information on the different sub-surface layers, depth, thickness, and distribution

of the fractured basement as potential sources of groundwater. The basement rocks consist of a migmatite-gneisses, granite

gneiss, and granite. The granite occurs in several locations of the study area. Twelve vertical electrical sounding stations were

established utilizing the Schlumberger electrode configuration. The electrical resistivity data obtained where interpreted using

IPI2win software. The results obtained from the analysis of the geophysical data showed that the study area is underlined by

three geo-electrical layers. These layers are the topsoil, weathered layers, and fractured basement. The top soil layer of

thickness and resistivity values ranging from 1.31-2.16m and 236-990 ohms meters, weathered layer ranging from 1.22-5.19m

and 33.8-213 ohms meters and the fractured basement ranging from infinity in thickness and 397-966 ohms meters. Also, the

study area lacks sufficient fractures and the thickness of the overburden was also thin for groundwater exploration activities.

Keywords

Gwagwalada, Granite Gneiss, lithology, potential, Schlumberger, Tungamaje, Zuba

Received: July 3, 2015 / Accepted: August 9, 2015 / Published online: August 19, 2015

@ 2015 The Authors. Published by American Institute of Science. This Open Access article is under the CC BY-NC license.

http://creativecommons.org/licenses/by-nc/4.0/

1. Introduction

Groundwater occurrence is greatly influenced by the geology,

topography and climatic factors that prevailed in a given

area. By the same fact, the hydro-geologic condition of

Gwagwalada area council is mainly controlled by the

geology and geological structure. Geological structures

(faults, fractures and lithologic contacts) play a great role in

the movement occurrence of groundwater in the study area,

the area is characterized by rocks like granite, pegmatite,

shiest and gneiss which are Precambrian in nature

groundwater occurs in the basement complex in the

weathered mantle or in the joint and fracture systems in the

unweathered rocks. The area under study belongs to the

Precambrian era. It is underlain by the Nigerian basement

complex rock of the Precambrian age. Weathering and other

denudational activities have made parts of the under laying

rock mass to be slightly thicker in some areas than others.

The area has a fairly plain topography with sparsely

distributed medium size hills and highlands that may have

been formed by outcropping basement rocks. The basement

rocks consist of a migmatite-gneisses, granite gneiss, and

granite. The migmatite-gneiss is the most wide spread rock

unit. The granite occurs in several locations. Detailed reports

Physics Journal Vol. 1, No. 2, 2015, pp. 97-104 98

of the lithological description, age, history, structure and

geochemistry of the Basement Complex of Nigeria are given

in Oyawoye, 1972; Black et al., 1979; Rahaman, 1988; Caby,

1989, and Dada, 2008. In Fig. 1 the blue arrow indicates the

location of Abuja on the geologic map of Nigeria. In the

study area, all the three major rock categories mentioned

above are well represented in Fig. 2. The rocks are generally

weathered into reddish micaceous sandy clay to clay

materials, capped by laterite (Obaje, 2009).

The choice of a particular method is governed by the nature

of the terrain and cost considerations [Emenike, 2001].

Fig. 1. Geological map of Nigeria, showing the position of Abuja (blue arrow) in the basement complex of north central Nigeria (modified from Obaje, 2009).

2. Geology of Study Area

The study area is zuba and Tungamaje in Gwagwalada Area

Council, is part of the basement complex of Nigeria

considered by various workers to be Precambrian to lower

Paleozoic in age (Oyawoye, 1970 and Rahman, 1976). Zuba

is located in the North Central part of Nigeria. It is situated

along Kaduna–Lokoja road, it is located at an elevation of

432 meters above sea level and its population amounts to

536,068 (cencus,2006). Its coordinator are latitude 90 05

1 47

11

N and longitudes 70 12

1 46

11 E. The Abuja Guide, a National

Space Research and Development Agency Atlas of 2002,

Abuja is located between latitudes 80 10

1 and 9

0 45

1 North

and longitudes 60 30

1 and 7

0 45

1 East.

The area of study forms part of the Basement Complex of

north central Nigeria; with lithologic units falling under three

main categories, which include (1) Undifferentiated

migmatite complex of Proterozoic to Archaean origin, (2)

Metavolcano-Sedimentary rocks of Late Proterozoic age and

(3) Older Granite Complex of Late Precambrian - Lower

99 Adeeko Tajudeen Olugbenga and Ojo Emmanuel Osiewundo: Determination of Subsurface Delineation Using Electrical

Resistivity Sounding in Zuba and Environs of Gwagwalada Area Council, Abuja, North Central, Nigeria

Palaeozoic age, also known as Pan-African Granites Ajibade

et al., 1987. All these rocks have been affected and deformed

by the Pan-African thermotectonic event. The rocks of the

area are generally quartz-rich acidic types which account for

the generally sandy nature of the soil. There is however, one

major advantage about the type of rocks and soils found in

the area because of the availability of construction materials

in the form of building stones, quartz and pistolitic gravel,

building sands and earth for use as foundation materials, as

well as pottery raw materials. Figure 3 shows the geological

map of Abuja showing Gwagwalada area council. The

amount of rainfall in the area is moderate between the

months of April and October and the dry season which begins

from October–November and last until March-April,

although there could be some scanty flashes of rain during

this period. However, within these seasons is a brief

harmattan season that is occasioned by the north east trade

wind and the attendant dust haze, increased cold and dryness.

Weather conditions in the area are influenced by its location

within the Niger–Benue trough on the windward side of the

Jos Plateau and at the climate transition zone between the

essentially ‘humid’ south and ‘sub-humid’ north of the

country. The high temperatures and the relative humidity in

the Niger-Benue trough give the area a heating effect.

Fig. 2. Geological map of the study area and showing positions of VES points.


Fig. 3. Geological Map of Abuja (source: Geology Unit of Bwari Area Council August, 2014).

3. Material and Method

The electrical resistivity method utilized the Vertical

Electrical Sounding (VES) is used to measure vertical

variations in electrical properties beneath the earth surface

involving the schlumberger array, ABEM Terrameter SAS

300C was used to acquire resistivity data. Field equipment,

include: Terrameter, current and potential electrodes, long

conductors with crocodile clips, hammers, field survey tapes

and mobile phones for communication. The Resistance

measurements are made at each expansion and multiplied by

the respective geometric factor (K) to give the resistivity. A

total of twelve VES soundings were carried out along the

study area. The electrode separation (AB/2) varied from 1.5

to 150 m was used with the aim of probing a depth of at least

1/3 of AB. The VES station were marked, two current

electrodes (C1 and C2) of equal distances on the opposite

side of the VES station were measured and hammered into

the ground. Similarly, two other electrodes (P1 and P2) of

equal distances at VES point between the current electrodes

were measured. The obtained field dates were subjected to

analysis and interpretation by computer iterations using

Ipi2Win Software.

4. Result and Discussion

A total number of twelve (12) VES were carried out, six in

each of the two locations. The results of the interpretation

were used to determine the expected subsurface geologic and

hydro-geologic features of the water bearing rocks. The

interpreted result of the vertical electrical sounding data

revealed the different geo-electric layers in terms of their

resistivities and depths in the study area. The software used

in the processing of the raw data works in such a way that it

merges neighbouring layers of slightly different resistivities

in order to minimize the layers detected. The sounding curves

show three layer earth models. The three layer curve

Characterized by H curve types covered 100% of the study

area. The rocks within this basement complex are grouped

into three categories; these are the older granites, gneiss and

mignetite; the older metasediments; and the younger

metasediments. According to Ajibade and Wright (1980), the

rocks of the basement complex are believed to have evolved

in at least four orogenic events namely: the pan African

(600±150My), The Kibaran (1100±200My), The Eburnian

(2000±200My) and the Liberian (2800±200My). The

migmatite–gneiss complex dominates the basement complex

in the study area consisting of fairly uniform biotite and

biotite–hornblende–gneisses with locally intercalated bands

of amphibolites and quartzite (Geological Survey of Nigeria,

1986).

The result of the geophysical investigation revealed three

subsurface geo-electrical layers in all the VES stations. The

observed geo-electric sections include the top soil layer,



weathered layer, and fractured basement. The top layer

resistivity values ranges from 236 to 990 ohm-m, with mean

resistivity of 528.25 ohm-m. Its highest value was observed

at VES 12 and the lowest at VES 01 (as seen in fig. 4). The

top layer thicknesses range from 1.31 to 2.16m, with mean

thickness of 1.7892m. It highest value was observed at VES

07 and the lowest at VES 06. The second layer constitutes the

weather layer and its resistivity values range from 33.8 to

213Ωm with mean resistivity of 67.33Ωm (as seen in fig. 5).

The highest value was observed at VES 06 and the lowest at

VES 02. Its thicknesses range from 1.22 to 5.19m, with mean

thickness of 2.992m. The highest thickness was observed at

VES 06 and the lowest at VES 02 (as seen in fig. 7 and fig.

8). The third layer which constitutes the fractured basement

which has resistivity values that range from 297 to 966 ohm-

m, with mean resistivity of 539.42 ohm-m. Its highest value

was observed at VES 8 and the lowest at VES 1(as seen in

fig. 6).

The lithology was used as a preliminary basis for rock type

identification, in the (FCT) (Edetand Okereke, 1985),

malomo et al, 1982/83, omeje et al, 2013 and the lithology of

the study area agree with the earlier study mention.

Table 1. Simulated Result of Resistivity Data from the Study Area.

VES Layers ρ ( Ω-m) Thickness(m) Depth(m) Probable Geological Section Curve types Coordinates

01

1 236 1.65 1.65 Top soil

H

9.0961113N

2 42.3 1.56 3.22 Weather layer

3 397 - Fractured basement 7.1958333E

02

1 249 1.85 1.85 Topsoil

H

9.094444N


3 420 - Fractured basement 7.211666E

03

1 261 1.87 1.87 Topsoil

H

9.095833N


3 400 - - Fractured basement 7.096111E

04

1 308 1.63 1.63 Topsoil

H

9.0963889N



05

1 322 1.93 1.93 Topsoil

H

9.09555N

2 51 1.64 3.56 Weather layer


06

1 955 1.31 1.31 Topsoil

H

9.095277N

2 213 5.19 6.49 Weather layer


07

1 612 2.16 2.16 Topsoil

H

9.095833N



08

1 405 1.65 1.65 Topsoil

H

9.0963886N



09

1 747 1.76 1.76 Topsoil

H

9.0969441N



10

1 714 2.15 2.15 Topsoil

H

9.096111N



11

1 540 1.86 1.86 Topsoil

H

9.0966663N



12

1 990 1.65 1.92 Topsoil

H

9.0963886N




Fig. 4. Topsoil Layer Iso-Resistivity.

Fig. 5. Weather Layer Resistivity.

Fig. 6. Fracture Basement.

Fig. 7. Weather Thickness.

9.094

LATITUDE

7.1

7.11

7.12

7.13

7.14

7.15

7.16

7.17

7.18

7.19

7.2

7.21

LONGITU

DE

200

240

280

320

360

400

440

480

520

560

600

640

680

720

760

800

9.094

LATITUDE

7.1

7.11

7.12

7.13

7.14

7.15

7.16

7.17

7.18

7.19

7.2

7.21

LONGIT

UDE

35

45

55

65

75

85

95

105

115

125

135

145

155

165

175

9.094

LATITUDE

7.1

7.11

7.12

7.13

7.14

7.15

7.16

7.17

7.18

7.19

7.2

7.21

LONGIT

UDE

380

400

420

440

460

480

500

520

540

560

580

600

620

640

660

680

700

720

740

760

780

800

820

9.094

LATITUE

7.1

7.11

7.12

7.13

7.14

7.15

7.16

7.17

7.18

7.19

7.2

7.21

LONG

ITUDE

1.3

1.5

1.7

1.9

2.1

2.3

2.5

2.7

2.9

3.1

3.3

3.5

3.7

3.9

4.1

4.3



Fig. 8. 3D of Weather Thickness.

5. Conclusion

This study has been able to shown the importance of

resistivity method in determine the lithology of an area. The

geophysical investigation carried out delineates the presence

of three subsurface layers which comprised the top soil

which is composed of sandy clay or clayey sand, weathered

layer which due to the low resistivity of the VES point for

this layer, there is indication of possible clay materials within

the weathered layer, and fractured basement rock cannot

sustain boreholes. The basement rocks consist of a

migmatite-gneisses, granite gneiss, and granite. The

migmatite-gneiss is the most wide spread rock unit. In zuba

and tungamaje, the rock compositions are made up of

granites; granite gneiss gave relatively higher yields in the

faulted zones or apparently fractured which could be the

evidence of volcanic activity marked by the occurrence of

flat toped lateritised basalt. There should be a thorough

investigation of rock to determine its characters and

properties within the area.

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