interpretation of aeromagnetic data over gboko using spi and analytical method

INTERPRETATION OF AEROMAGNETIC DATA OVER GBOKO USING

SOURCE PARAMETER IMAGING AND ANALYTICAL SIGNAL

BY

OJOTU KAZEEM ABDULLAHI2009/1/33307BP

DEPARTMENT OF PHYSICSSCHOOL OF PHYSICAL SCIENCE

FEDERAL UNIVERSITY OF TECHNOLOGYMINNA; NIGER STATE

NOVEMBER; 2014INTERPRETATION OF AEROMAGNETIC DATA OVER GBOKO USING

SOURCE PARAMETER IMAGING AND ANALYTICAL SIGNAL

BY

OJOTU KAZEEM ABDULLAHI2009/1/33307BP

A PROJECT REPORT SUBMITTED TO PHYSICS DEPARTMENT, FEDERALUNIVERSITY OF TECHNOLOGY, MINNA IN PARTIAL FULFILLMENT FOR THE

AWARD OF BACHELOR OF TECHNOLOGY (B.TECH) DEGREE IN PHYSICS/ ELECTRONICS

NOVEMBER; 2014

DECLARATION

I declare that the project report titled, “Interpretation of

Aeromagnetic Data over of Gboko using Source Parameter

Imaging and Analytical signal” has been performed by me in the

Department of Physics. The information derived from the

literature has been duly acknowledged in the text and list of

references provided. No part of this project report was

previously presented for another degree or diploma at any

university.

Sign……………………………. Date………...……… Ojotu Kazeem Abdullahi

i

CERTIFICATION

This project report entitled “Interpretation of Aeromagnetic

data over of Gboko using Source Parameter Imaging and

Analytical signal” by Ojotu Kazeem Abdullahi meets the

regulations governing the award of the degree of bachelor of

Technology in physics of Federal University of Technology,

Minna and is approved for its contribution to knowledge and

literary presentation.

...............................................

......................................Mr Adetona, A DateProject Supervisor

ii

...............................................

......................................Dr Uno, E.U DateHead of Department

...............................................

........................................External Examiner Date

DEDICATION

I dedicate this report work to Almighty Allah for his guidance

and sustenance he gave to me till this moment I’m truly

grateful to him.

iii

I also dedicated to my parents Mr. and Mrs. Abdullahi Ojotu

whom without their effort I would not be opportune to be in

this school and who stands with me through my academics

endeavor. May Allah continue to bless them abundantly (AMIN).

ACKNOWLEDGEMENTiv

My sincere appreciation goes to Almighty Allah for his love,

care and guidance over me throughout my academic pursuit.

My appreciation goes to Mr. Adetona Abbass, who plays a

fatherly role and a mentor in the supervision of this project.

Many thanks go to all the departmental lecturers, departmental

secretary and my HOD; Dr Uno, E.U.

Special thanks to Mr Dada Michael for his support throughout

the entire duration of this program.

I am grateful to my dad, late Mr. Abdullahi Ojotu, whose

absence has made me stronger, my Mum, Mrs. Asmau Ojotu for his

support; prayerfully, financially and morally and My wonderful

sibling; Ismail, Rabiat, Munirat, Halimat and my cousins whose

trust kept lifting me higher.

All my friends; Adimchinobi, My “Elwaziri clique”I see you, my

Precious jewel; Jesuseun, faith, Awwal, Salisu, Mrs Ekeno,

Timacool, Farhat, hussy of life, my roommates; zeeky and

Tankocaine, compound mates; sexy-tee of life, Miscutie,

Khamon, Idih, Mary, Rahmat(cousin of life), Joy Lemba and so

many others, thanks for being part of this chapter of my life.

v

My project colleague; Shakirat, whose assistance was priceless

during this project work.

And my newly added family, Mr. and Mrs. Emeka Coleman C., who

supported me during this course would not be left out I thank

you.

ABSTRACT

The IGRF filtered Aeromagnetic data over Gboko, a town incentral part of Nigeria within the lower Basin was subjectedto vertical and horizontal analysis, Source Parameter Imagingand Analytical Signal. This reveals the geophysicalinformation such as Minimum depth within the study area is95.527m and these exist within North-western region, lower-midportion and north-eastern corner of the study area. Themaximum depth of 8323m was observed around south-westernregion. The amplitude response equally shows amplitude from0.029 to 2.730 nT/M is region with outcrops, amplitude rangingfrom 0.011nT/M to 0.03 nT/M is intrusive bodies while areawith thick sediment has amplitude ranging from 0.00nT/M to0.011 nT/M. Correlation between depth and amplitude responsereveals that the region with high amplitude shows shallowdepth while region with high depth shows low amplitude.

vi

TABLE OF CONTENTS

Cover page

Declaration

i

Dedication

ii

Certification

iii

vii

Acknowledgement

iv

Abstract v

Table of content

vi

List of figures

viii

CHAPTER ONE; INTRODUCTION

1.1 Back ground of the Study

1

1.2 Geophysics and Geophysical Survey

2

1.3 Aeromagnetic Survey and its application

3

1.4 Location of study area

4

1.5 Source of data

5

1.6 Statement of Problems

6

viii

1.7 Aim and Objectives

6

1.8 Justification of study

7

CHAPTER TWO; LITERATURE REVIEW

2.1 Geology of the Study area

8

2.2 Review of Geological Work in the Lower Benue Trough

9

2.3 Review of Geophysical works in the Lower Benue Trough

10

CHAPTER THREE; MATERIALS AND METHOD

3.0 Method of Study

13

3.1 Data Acquisition

14

3.2 Data Analysis

14

ix

3.2.1 Production of Total Magnetic Intensity

14

3.2.2 Fourier Filtering of magnetic data

14

3.2.3 Reduction to pole

16

3.2.4 Reduction to Equator

20

3.2.5 First Vertical Derivatives (1VD)

20

3.2.6 Horizontal Derivatives (DX,DY and DZ)

21

3.3 Depth Analysis

22

3.3.1 Analytical signal

22

3.3.2 Source Parameter Imaging (SPI)

24

CHAPTER FOUR; RESULT AND DISCUSSION

x

4.1 TMI map of Study Area

28

4.2 TMI Reduced to Equator (RTE)

28

4.3 Horizontal Derivatives

29

4.4 First Vertical Derivative

29

4.5 Analytical Signal

30

4.6 Source Parameter Imaging

4.7 Correlation of Results from Analytical Signal and SPI

CHAPTER FIVE; CONCLUSION AND RECOMMENDATION

5.1 Conclusion 40

5.2 Recommendation

41

REFERENCE 42

LIST OF FIGURES

xi

Chapter 1; Figure 1.0: Showing the main division of the Earth

33

Chapter 2; Figure 2.1 Geological map of the study area

34

Chapter 4; Figure 4.1 TMI map of study Area

36

Chapter 4; Figure 4.2 Reduced to Equator

37

Chapter 4; Figure 4.3 Horizontal derivative DX

38

Chapter 4; Figure 4.4 Horizontal derivative DY

39

Chapter 4; Figure 4.5 First vertical derivative (1VD)

40

Chapter 4; Figure 4.6 Analytical signal

41

Chapter 4; Figure 4.7 Source Parameter Imaging

42

Chapter 4; Figure 4.8 Showing profile lines on the Analytical

Signal result 43

Chapter 4; Figure 4.9 Showing profile lines on the SPI result

44xii

Chapter 4; Figure 4.10 Grid analysis of profile one

45

Chapter 4; Figure 4.11 Grid analysis of profile two

45

Chapter 4; Figure 4.12 Grid analysis of profile three

46

Chapter 4; Figure 4.13 Grid analysis of profile four

46

Chapter 4; Figure 4.14 Grid analysis of profile five

47

Chapter 4; Figure 4.15 Grid analysis of profile six

47

xiii

CHAPTER ONE

INTRODUCTION

1.1 Background of Study

Based on geomagnetism, the earth may be considered as made up of

three parts: core, mantle and crust (figure 1). Convection

processes in the liquid part of the iron core give rise to a

dipolar geomagnetic field that resembles that of a large bar-

magnet aligned approximately along the earth's axis of rotation.

The mantle has little effect on earth's magnetism, while

interaction of the geomagnetic field with the rocks of the

Earth's crust produces the magnetic anomalies recorded in

detailed surveys carried out close to the earth's surface (Reeves

2005). Thus an anomaly is created when the earth’s magnetic field

is disturbed by an object that can be magnetized. Survey data is

interpreted based on the assumption that magnetic sources must

lie below the base of the sedimentary sequence. This allows rapid

identification of hidden sedimentary basins in mineral

exploration. The thickness of the sedimentary sequence may be

mapped by systematically determining the depths of the magnetic

1

sources over the survey area. Depths to the magnetic basement are

very useful in basin modeling such as determination of source

rock volume and source rock burial depth. The identification and

mapping of geometry, scale and nature of basement structures is

critical in understanding the influence of basement during rift

development, basin evolution and subsequent basin inversion.

From regional aeromagnetic data sets, information such as

tectonic frame of the upper crust can be obtained. The patterns

and amplitude of anomalies reflect the depth and magnetic

character of crystalline basement, the distribution and volume of

intrusive and extrusive volcanic rocks and the nature of

boundaries between magnetic terrains.

1.2 Geophysics and Geophysical survey

Geophysics is defined as the physics of the earth and its

surrounding atmosphere. That is to say, that geophysics has to do

with all aspects of the physics of the earth, atmosphere and one

might add today-space. The subject of geophysics includes

seismology, thermal properties of the earth, meteorology,

atmospheric electricity or ionosphere physics, terrestrial

magnetism etc. The aim of pure geophysics is to deduce the2

physical properties of the earth and its internal constitution

from the physical phenomena associated with it, for instance the

geomagnetic field, the heat flow, the propagation of seismic

waves, the force of gravity etc.

On the other hand, the objective of applied geophysics is to

investigate specific, relatively small scale and shallow

features, which are presumed to exist within the earth crust.

Among such features may be synclines and anticlines, geological

faults, salt domes, undulation of the crystalline bedrocks under

a cover of moraine, ore bodies, clay deposits etc. The

investigation of such features very often has a bearing on

practical problems of oil prospecting, location of water- bearing

strata, mineral exploration, highway construction and civil

engineering. The application of physics, in combination with

geological information is the most or only satisfactory way

towards a solution to these problems.

The various geophysical techniques for gathering information

about subsurface features all depend in one way or another, on

differences in electric, magnetic, or elastic properties of rocks

and sediments. The techniques may be classified as passive or

3

active. In the passive category, exiting force fields are

measured directly without instrumentally generated signals, and

the results are interpreted in terms of subsurface features

perturbing the field, Magnetic, thermal and gravity measurements

fall in this category. In the active category, instrumentally

generated signals pass through the subsurface and are then

detected and recorded, seismic technique, electromagnetic

techniques, earth resistivity measurements and ground-penetrating

radar are all active devices.

1.3 Aeromagnetic Survey and its Applications

Aeromagnetic survey is one of the common types of geophysical

survey carried out using a magnetometer aboard or towed behind an

aircraft. The principle is similar to a magnetic survey carried

out with a hand-held magnetometer, but allows much larger areas

of the earth’s surface to be covered quickly for regional

reconnaissance. The aircraft typically flies in grid-like pattern

with height and line spacing determining the resolution of the

data (and survey of the cost per unit area).

4

As the aircraft flies, the magnetometer records tiny variations

in the intensity of the ambient magnetic field due to the

temporal effects of the constantly varying solar wind and spatial

variations in the earth’s magnetic field, the latter being due to

both the regional magnetic fields and the local effect of

magnetic minerals in the earth’s crust. By subtracting the solar

and regional effect, the resulting aeromagnetic map shows the

spatial distribution and relates abundance of minerals (most

commonly the iron oxide mineral magnetite) in the upper levels of

the crust. Because different rock types differ in their content

of magnetic minerals, the magnetic map allows a visualization of

the geological structure of the upper crust in the subsurface,

particularly the spatial geometry of bodies of rock and the

presence of faults and folds. Aeromagnetic data is more commonly

expressed as collared and shaded computer generated. From

regional aeromagnetic data sets, information such as tectonic

frame of the upper crust can be obtained. The patterns and

amplitude of anomalies reflect the depth and magnetic character

of crystalline basement, the distribution and volume of intrusive

and extrusive volcanic rocks and the nature of boundaries between

5

magnetic terrains. The application of aeromagnetic survey is as

follows (Adetona and Abu 2005).

i. Direct detection of deposits of certain iron ores.

ii. In oil exploration, aeromagnetic data can give

information from which the depths to basement rocks can

be determined and thus locate and define the extent of

sedimentary basins. Sedimentary rocks however exert such

a small magnetic effect compared with igneous rocks that

virtually all variations in magnetic intensity

measurable at the surface result from topographic or

lithologic changes associated with the basement or from

igneous intrusions.

iii. Recognition and interpretation of faulting, shearing,

and fracturing not only as potential hosts for a variety

of minerals, but also an indirect guide to epigenetic,

stress related mineralization in the surrounding rocks.

iv. Identification and delineation of post-tectonic

intrusive. Typical of such targets are zoned syenite or

6

carbonatite complexes, kinerlites, tin-bearing granites,

and mafic intrusions

1.4 LOCATION OF THE STUDY AREA

The area covered by the aeromagnetic survey described in this

thesis is located at the extreme northeastern end of the Lower

Benue Trough with transition into the Middle Benue Trough called

Gboko (Sheet 271). The area lies between latitude 830N and 900N

and between 700E and 730E. The area has been given less

attention with regards to geological studies than the other parts

of the Lower Benue Trough or the Middle Benue Trough. Figure 2

shows the map Nigeria showing the location of the study area.

7

Figure 1.1: Map of Nigeria showing the study area (adapted from the Geological and Mineral Map of Nigeria, 2009, Nigerian Geological Survey Agency).

1.5 SOURCE OF DATA

New dataset from Nigerian Geological Survey Agency was used for

this work, it’s from the new high-resolution airborne survey

coverage in Nigeria carried out by Fugro airborne survey at

826,000 line-km of magnetic and radiometric surveys flown at 500

8

Study Area

m line spacing and 80m terrain clearance in 2009. It’s of higher

quality than the 1970s and in digitized form as well. This work

cover only one aeromagnetic map having sheet number 271 (Gboko)

and the maps are on scale of 1:100,000 and half-degree sheets

contoured mostly at 10nT.

1.6 Statement of Problem

In mineral exploration, the structural surface interpreted from

magnetic depth estimates is often the best available

approximation to the true crystalline metamorphic/igneous

basement configuration and estimate of basement depth sedimentary

thickness is a primary exploration risks parameter. Specifically,

the magnetic basement is very relevant in the application of

magnetism to mineral exploration. Nigeria economy is solely

dependent on the crude oil found on the Niger Delta region hence

there is need to identify other possible source of mineral in

other regions.

1.7 AIM AND OBJECTIVE

9

The aim of this work is to determine the depth to the magnetic

rocks within gboko area and locate the position and extent of

magnetic intrusions. The procedures involve in achieving this aim

are as follows:

i. Production of Total Magnetic Intensity (TMI) map of the

study area using MONTAJ software.

ii. Perform vertical derivative of the TMI data to enhance

shallow geological features and horizontal derivative to

identify geology boundaries in the profile data.

iii. Evaluating the horizontal derivative of the field data in x,

y and z directions

iv. Depth evaluation of buried magnetic rocks will be determined

using Analytical Method.

v. Depth evaluation using Source Parameter Imaging.

1.8 JUSTIFICATION OF STUDY

The aeromagnetic data sheet 271 is a product of Nigeria

Geological Survey Agency (NGSA), they undertook an Aeromagnetic

survey and the digitizing of aeromagnetic data in all parts of

Nigeria between the year 2000 and 2009. The previous aeromagnetic

10

data carried out between 1974-1980 was collected at a flight

altitude of 152.4m along N-S and flight lines spaced

approximately 2000m while the recent aeromagnetic data were

collected at a nominal flight altitude of 80m meters and flight

line spacing of 500m. The maps are on a scale of 1:100,000 and

half degree sheets. This project is intended to determine the

depth of magnetic rocks of the study area using this new dataset.

CHAPTER TWO

LITERATURE REVIEW

11

2.1 Geology of the Study Area

The study area lies in the Lower Benue trough which is a linear

depression filled with up to 6km of Cretaceous (Albian-

Maastrichtian) sediments. The earlier (Albian-Santonian)

sediments in the trough are mainly marine in character and their

deposition was terminated by an episode of deformation in the

Santonian (Burke et all 1970). Following this deformation, the

marine sediments were eroded and deltaic sediments spread

throughout the trough. Continental facies sedimentation persisted

until the end of the Cretaceous, apart from a short lived but

extensive marine incursion in the Maastrichtian (Burke et al

1970) and (Carter et al 1963). Nwachukwu (1972) has described

evidence for a period of slight deformation in the Cenomanian.

Reviews of the geological history and theories on the origin of

the Benue trough have been presented by (Burke et a1. 1970),

(Olade 1975) and (Wright 1976). The interpretation of the Benue

trough as a rift valley is supported by the recognition of a

positive Bouguer anomaly (Cratchy and Jones 1965), coincident

with the axis of the trough and associated closely with a belt of

brine springs and Cretaceous Pb-Zn and barites mineralisation.12

Burke et a1 drew an analogy between the Benue trough and the Red

Sea and proposed that the Benue trough formed one arm of a

Cretaceous RRR triple junction which subsequently failed to

develop while the other two arms gave rise ultimately to the

South Atlantic Ocean (Burke et a1.1970,1971). Grant has presented

a similar model in which the northern coast of the Gulf of Guinea

developed as a transformed fault rather than as a ridge (Grant

1971). The Benue trough is unique among rift valleys in that it

is filled with sediments which have been folded along axes

parallel to its length (Burke et al 1970). The folds are

generally large but with dips rarely exceeding 300. Burke et a1

explain this folding by postulating that the Benue trough

underwent active sea-floor spreading during the early Cretaceous

and that the new oceanic crust was subsequently consumed by

subduction during the Santonian. The resulting "orogeny" was

responsible for the observed folding. They cite as evidence for

this subduction episode the discovery of "more than 1300 m of

andesitic and basaltic lavasand tuffs" of about Santonian age in

boreholes sunk into the Niger delta (Burke et a1. 1971). Volcanic

rocks underlie the earliest Albian sediments in the core of the

13

Abakaliki anticlinorium in the lower Benue valley (Uzuakpunwa

1974). Olade (1978) has suggested that these volcanic rocks are

of alkaline affinities and were erupted during the early

development of the Benue rift. The geology of the study area is

shown in figure 2.0.

2.2 Review of Geological Work in the Lower Benue Trough

The geology of the Lower Benue Trough has been documented through

the tectono sedimentary studies of Murat(1972), Nwachukwu (1972),

Olade (1975) and Agagu and Adighije (1983). Reyment (1965),

Reyment and Mörner (1977) and Zaborski (2000) described the

transgressive and regressive cycles related to marine

sedimentation in the area. The tectonic evolution study of

Nwachukwu (1972) in terms of marine transgression and regression

reveals some stages of succession which are the Albian

transgression followed by the cenomanian regression and turonian

transgression. During the albien transgression, the gboko

formation, Akpagher Formation, Ikumbur Limestone and Mayange

Limestone were deposited, this was caused by the Tectonic

subsidence and South Atlantic sea-level rise (Najime 2011). The

transgression was followed by a regressive phase (Middle14

Cenomanian) during which the Gbemacha Sandstone were deposited in

the northern part of the area and the Nienga Sandstone in the

southeastern part (Najime 2011). The regressive phase was

followed by a second transgressive phase (Late Cenomanian to

Turonian) when the Ezeaku Formation was deposited in the

southwestern part of the area (Najime 2011). During the same

interval, the Makurdi Formation was deposited in its northern

part, the Tse-Agberagba Sandstone in the mid-southern part and to

the east the Lessel Sandstone was deposited. The third marine

transgression in the area (Late Turonian to Coniacian) deposited

the Awgu Shale in the western part (Najime 2011). The Asu River

Group sediments comprises predominantly of shales with localized

sandstones, siltstones and limestones (olade 1975) as well as

extrusive and intrusive material (Reyment 1965; Murat 1972;

Nwachukwu 1972 and Tijani et al 1997) of the Abakaliki Formation

in the Abakaliki area and the Mfamosing Limestone in the Calabar

Flank . In addition, Akande described the Asu River Group as

consisting of arkosic sandstones, volcaniclastics, marine shales,

siltstones and limestone which overly the Pre-Cambrian to Lower

Paleozoic crystalline basement rocks (Akande et al 2011). The Asu

15

River Group is interpreted as sediments of the first

transgressive cycle into the Lower Benue Trough. The marine

Cenomanian – Turonian Nkalagu Formation (black shales, limestones

and siltsones) and the inter fingering regressive sandstones of

the Agala and Agbani Formations (Cross River Group) rest on the

Asu River Group. During the Late Albian, sequence of sandstones,

limestones and shales with calcareous sandstones of Odukpani

Formation were deposited unconformable on the Basement rocks in

the Calabar Flank. Nwajide (1985) and Hoque (1984) described the

Makurdi formation which includes ezeaku formation as consisting

fluvial sandstone and mud rocks with a middle carbonate-bearing

wadatta member. Makurdi formations possess the clays and fine to

coarse grained sandstone overlying the Gbemcha sandstone in Gboko

area. The geological map of Gboko is shown in figure 2

2.3 Review of Geophysical works in the Lower Benue Trough

Many workers and researchers have focused a lot of attention on

the trough. These are aimed at depicting the nature and

characteristics of the structure. The earliest studies in the

Benue Trough were mainly aimed at exploring its origin and

tectonic evolution. However, the earliest geophysical16

investigations in the Lower Benue Trough were mainly centered on

the measurement and rather qualitative study of its gravity

field. Nkwonta and Kene (2005) employed various graphical methods

of aeromagnetic interpretation to determine the depth to the

buried magnetic anomalous structures in the Lower Benue trough.

They discovered that the depth to the top of the structure lies

between 0.55 and 9.20 km. They inferred that the magnetic

anomalies over parts of the trough could be explained by the

existence of the intrusive bodies and elevation of crystalline

basement. Ugboh and okeke studies of akataka and environs of the

lower benue trough reveals low Bouguer gravity anomalies with

magnitudes ranging from –2.5 to 3.8 mgals and with abrupt changes

at intervals thereby suggesting a fault, deposit of salt was also

suspected to be buried between depth of 868 and 2618m, the low

Bouguer gravity anomaly over the area suggests a zone of basic to

intermediate igneous intrusions, deep basement and crustal

thinning (Ugboh and Okeke 2010). Sedimentation study of Adetona

and Abu using Source Parameter Imaging method shows that the

maximum depth estimate is approximately 10 kilometers and a

minimum depth of 76.983 meters. Thus Results from Source

17

Parameter Imaging gives maximum thickness of sedimentation of

9.847 km, which also occur within Idah, Ankpa, and Udegi axis

(Adetona and Abu 2013). Nwugha et al uses peter’s maximum slope

method to obtained maximum depths of 6.72±0.58km between Oturkpa

and Ogbadibu town and 1.09km ±0.58km for minimum depths which

gives a sedimentary thickness of 5.63±0.58km along oturkpa and

ogbadibu axis, they also explained that the sequence of closed

lows east Oturkpa is due to largest part of an irregular

metamorphic basement that has been occupied with sediments or

faulted metamorphic occupied with sediments, fault was discovered

around Ogbadibu and Imane as well as Oturkpo area with signs of

discontinuous lineation and circular to cylindrical anomalies

( Nwugha et al 2012).

The result obtained from interpretation of aeromagnetic anomalies

over some parts of lower Benue trough by David and marius (2013)

reveals that there are two –layered source model i.e. the deeper

magnetic source whose depth vary between 1.6km and 6.13km with

the means value depth of 3.03km which representing magnetic

basement surface and the depth to the shallower magnetic source

vary from 0.06km and 0.37km with the mean value depth of 0.22km

18

indicate the present of magnetic intrusive bodies within the

basement (David and marius 2013)

CHAPTER 3

MATERIALS AND METHODS

3.1 Method of Study19

The Total Field map of Gboko (Sheet 271) was acquired. The

geomagnetic gradient was then removed from the map using the

International Geomagnetic Reference Field (IGRF) of 32000nT.

This research work, made use of OASIS MONTAJ software in the

production of the total magnetic field intensity (TMI) map which

was further subjected to different methods of filtrations to

enhance the map and define the features that were difficult to

detect before the filtering process. The filtering steps used are

i. The Total Magnetic Field map was reduced to equator in

other to remove the dependency of the magnetic field on the

angle of inclination.

ii. Performing vertical derivative of the resulting map to

enhance shallow geological features and horizontal

derivative in both x and y directions to identify

geological boundaries in the profile map.

Two methods of depth analysis were employed in this research work

which also involves the use of OASIS MONTAJ software and visual

interpretations. They are

20

i. Analytical signal method which measures the amplitude

response using the results from the horizontal derivatives

in x, y and z directions.

ii. Source Parameter Imaging method which uses the first and

second order derivatives of the Analytical signal to compute

depth response of an anomaly.

The detailed procedures and theories used for this research work

are as follows

3.1 Acquisition of Data

The aeromagnetic map used in this study was acquired from The

Nigerian Geological Survey Agency. The recent aeromagnetic data

acquisition and compilation was done by Fugro Airborne Surveys,

carried out between 2003 and 2010 which covers the entire land

mass of Nigeria. To achieve this, the Nigerian landmass was

divided into blocks. The magnetic data were collected at a normal

flight altitude of 100m along N-S and flight lines spacing of

100m at a speed approximately 2km apart. The data were then

published in the form of half degree by half degree (½˚ by ½˚)

21

aeromagnetic map on a scale of 1:100,000. The magnetic values

were plotted at 10nt (gamma) interval.

3.2 DATA ANALYSIS

3.2.1 Production of TMI map

TMI map was produced using computer software package called Oasis

mortaj with assistance from the project supervisor. The software

is an interactive computer program which places magnetic data

according to their longitude and latitude bearing and gives a

magnetic intensity map which is in colour aggregate

3.2.2 Fourier Filtering of the magnetic data

Magnetic data filtration is an important process that must be

carried out for analysis and interpretation. The objective of the

filter is to condition the data set and to render the resulting

presentation in such a way as to make it is easier to interpret

the significance of anomalies in terms of their geological

sources (Dale Bird, 1997). Therefore, the most effective way to

filter the data is with an understanding of the geologic control

and the desired filtered results. Several filtering techniques

22

can be performed in the frequency domain. However, in this study,

Fourier filtering method is used.

Generally, Fourier filters fall within one of the following

groups:

1. Sharpening filter that enhances the shorter wavelength

features in the data. These include high-pass filters,

downward continuations and vertical and horizontal

derivatives. Such filters are normally used to enhance

information from shallow geologic features.

2. Smoothing filters that enhance longer wavelength features in

the data, normally by removing or attenuating the shorter

wavelengths features. These include low-pas filters, upward

continuation and integrations. Smoothing filters are

normally used to remove short-wavelength noise in data or to

remove the effects of shallow geologic features.

3. Geophysical transformation that convert data from one

physical form to another. These include reduction to the

pole for magnetic data and the calculation of apparent

magnetic susceptibility apparent density.

23

Smoothing and sharpening filters are often combined to meet the

needs of a specific problem. For example, a vertical derivative

(sharpening filter that enhances near-surface geology) might be

combined with an upward continuation (smoothing filter that

reduces the effect of noise in the data). Filter can further be

described as geophysical filters – those whose outcome has a

geophysical basis or mathematical – those that have a

mathematical definition only. Since geophysical filters are based

on the physics of potential filed, they are ideally suited to

gravity and magnetic data whereas mathematical filters can be

applied to any kind of data.

Examples of geophysical filters are vertical continuations,

vertical derivative or integration, reduction to the pole and

apparent magnetic susceptibility or density. Mathematical filters

include horizontal derivative and the high and low pass filters –

Butterworth, Gaussian, cosine and simple high and low pass cutoff

filters.

In addition to filter, power spectra are often required. The

montaj geophysics system enable us to create a power spectrum of

24

the data and to place the real and imaginary components of the

Fourier transform into channels of the database.

Below are brief description of the theory, algorithm and

analytical processes that facilitate the basic interpretation

help us achieve the objectives itemized above.

3.2.3 Reduction to Pole

The vector nature of magnetic field, the superposition of

multiple magnetic sources and presence of geological and cultural

noises (such as noises due to pipe lines, power lines, railroads

and etc) increases the complexity of anomalies from magnetic

rocks, as a result, the interpretation of magnetic field data at

low magnetic latitude is difficult. Furthermore an observed

anomaly has asymmetric shape whenever magnetization occurs in

anywhere rather than magnetic poles. To harness this problem, the

best approach is to reduce the data to the magnetic pole where

the presumably vertical magnetization vector will simplify

observed anomalies. The aim of Reduction to the Pole is to take

an observed total magnetic field map and reproduce a magnetic map

that would have been observed if the survey had been conducted in

25

the magnetic pole and changes the asymmetric form of observed

anomalies to the symmetric form. This reduces the complexity of

the observed anomalies. Data observed in low latitudes require

some special treatment of North-South features due to high

amplitude corrections needed for these features. Assuming induced

magnetization of all magnetic sources, pole reduction can be

calculated in the frequency domain using the following operator

(Grant and Dodds, 1972):

L(θ) = 1

[sin (I )+icos (I)cos (D−θ) ]2

(3.1)

Where:

θ is the wave number direction

I is the magnetic inclination

D is the magnetic declination.

The amplitude component is represented by the sin (I) term while

the phase component is given by the icos (I) cos (D – 0 ) term.

26

However, implementation of this method in the frequency domain

causes some problems; It is unstable in low latitude, for body

with unknown remanent magnetization it gives incorrect results,

induces synthetic noise to the data and lastly, frequency domain

implementation of this technique, demands that the inclination

and declination values should be fixed entire the survey area.

From (1), it can be seen that as I approaches 0 (the magnetic

equator) and (D-θ) approaches π /2 (a North – South feature), the

operator approaches infinity (Mendonca and Silver, 1993).This

effect as illustrated by figure 3.1, compares the magnetic

anomalies over an East-West and North-South vertically dipping

dyke-like body.

27

Figure 3.1: The shape of total magnetic field profiles over

a vertically dipping dyke-like body

For the East-West striking dyke, the amplitude remains constant

while the phase changes(shape). For the North-South striking

dyke, the anomaly shape remains the same at all latitudes but the

amplitude varies for different latitude. Reduction to pole

28

West-to-East profile

South-to-North profile

involves correcting the shape of East-west features and

correcting the amplitude of North-South features to produce the

same profile as would be observed at an inclination of 90°.

At low attitude, the amplitude disappears, thus amplitude must be

corrected. In the process of correcting the amplitude of this

North-South feature, noise component and magnetic effects from

bodies magnetized in the directions different from the induced

field will be amplified. Many authors have addressed the noise

problem of which the simplest and most effective technique is

that developed by Fraser Grant and Jack Dodds.

Grant and Dodds (1972) addressed this problem by introducing a

second inclination (I’) that is used to control the amplitude of

the filter near the equator:

L(θ) = 1

[sin (I’)+icos (I)cos (D−θ) ]2

(3.2)

Where I’ is inclination for amplitude correction

In practice, (I’) is set to an inclination greater than the true

inclination of the magnetic field. Anomaly shapes will be

29

properly reduced to the pole by using the true inclination (I) in

the complex term of equation (3.2). But by setting I’ ¿ I,

unreasonably large amplitude corrections are avoided. Controlling

the operator now becomes a matter of choosing the smallest I’

that will give the acceptable results.

Although the amplitude correction of the reduction to pole can be

easily corrected using equation (3.2), it is only valid for

induced magnetized bodies and remains invalid for remanently

magnetized bodies. It would be preferable to produce a result

that simply provides a measure of the amount of magnetization

regardless of direction.

3.2.4 Reduction to Magnetic Equator

Reduction to the equator is used in low magnetic latitudes to

centre the peaks of magnetic anomalies over their sources. This

can make the data easier to interpret while not losing any

geophysical meaning. Reducing the data to the equator (RTE) does

much the same thing, but at low latitudes, a separate amplitude

30

correction is usually required to prevent North-South signal in

the data from dominating the results.To reduce magnetic data to

equator we apply the equation,

L(θ)=[sin(I)−i.cos(I).cos(D−θ)]2X (−cos2 (D−θ ))

[sin2 (Ia)+cos2 (Ia ).cos2 (D−θ ) ]X [sin2 (I)+cos2 (I ).cos2 (D−θ )],if(|Ia|)<(|I|),Ia=I

(3.3)

Where

I = geomagnetic inclination

Ia = inclination for amplitude correction

D = geomagnetic declination

Sin (I) is the amplitude component while icos(I)cos(D-θ) is the

phase component

This is a method of removing the dependence of magnetic data on

the angle of magnetic inclination. This filter converts data

which have been recorded in the inclined earth’s magnetic field

at the equator to what the data would look like if magnetic field

had been vertical.

31

3.2.5 FIRST VERTICAL DERIVATIVE (1VD)

Spatial resolution can also be achieved using the vertical

derivative filter. The first vertical derivative filter computes

the vertical rate change in the magnetic field. A first

derivative tends to sharpen the edges of anomalies and enhance

shallow features. The vertical derivative map is much more

responsive to local influence than to broad or regional effect

and therefore tends to give sharper picture than the map of the

total field.

Vertical derivative

L(r )=rn (3.4)

Where n is the order of differentiation. And r is the wave number

(radians/ground unit) Note: r = 2πk where k is cycles/ground

unit. Ground unit is the survey ground units used in the grid

(eg. meter, feet etc.).The vertical derivative is commonly

applied to total magnetic field data to enhance the shallowest

geologic sources in the data. As with other filters that enhance

32

the high-wave number components of the spectrum, low-pass filters

is apply to remove high-wave number noise.

3.2.6 Horizontal Derivatives

The vertical derivative tends to sharpen the edge of anomalies

and enhance shallow features. the resultant map is much more

responsive to local influence than to bread or regional deep

seated anomalies.

Derivative in the X direction is given by the algorithm,

L(μ)=(μii)n 3.5

n is the order of differentiation, and µ represents the X

component of the wavenumber and ii = .

While the horizontal derivative in the Y direction is given by

L(V)=(Vi)n (3.6i)

Where n is the order of differentiation V represents the Y

component of the wavenumber and

33

i = ∂f∂x

(3.6ii)

Total horizontal derivative is a good edge detector because it

computes the maxima over the edges of the structures.

Total Horizontal derivative is given as;

THDR =√[∂T∂x ]

2+[∂T∂y ]

2 (3.7)

The horizontal gradient method measures the rate of change in

magnetic susceptibility in the x and y directions and produces a

resultant grid. The gradients are all positive making this

derivative easy to map.

3.3 Depth analysis

Two methods have been employed for the analysis of depth to

basement rocks within the study area, these are analytical method

and Parameter Imaging (SPI), and these two are briefly discussed.

3.3.1 Analytical signal

34

The analytical method gives the amplitude response of an anomaly.

This filter applied to magnetic data is aimed at simplifying the

fact that magnetic bodies usually have positive and negative peak

associated with it, which may make it difficult to determine the

exact location of causative body. For two dimensional bodies a

bell shaped symmetrical function is derived and for a three

dimensional bodies the function is amplified of analytical

signal. This function and it derivatives are independent of

strike, dip, magnetic declination, inclination and remanent

magnetization (Debeglia and Corpel 1997).

The analytic signal or total gradient is formed through the

combination of the horizontal and vertical gradients of the

magnetic anomaly. The analytic signal has a form over causative

body that depends on the locations of the body (horizontal

coordinate and depth) but not on its magnetization direction.

This quantity is defined as a complex function that its real

component is horizontal gradient and its imaginary component is

vertical gradient. Nabighian, (1972,1984) was able to prove that

the imaginary component is Hilbert transform of real component.

35

Consider M(x, z) be 2-D Magnetic field that measured along x-

axis, then the analytical signal, a(x,z) can be expressed in

terms of vertical and horizontal gradient of M(x, z) with respect

to x and z direction in Cartesian coordinate as followed

(Blakely, 1995)

a(x,z)= ∂M∂x+i ∂M∂z 3.8

where ∂M∂x and ∂M∂z are Hilbert transform pair. The amplitude for

the 2D signal is giving by

|A(x,z)| = √(∂M∂x )²+(∂M∂z)² 3.9For the 3-D case, the analytic signal is given by

a(x,z)= ∂M∂x+∂M∂y

+i ∂M∂z 3.10

The amplitude of the analytic signal in the 3-D case given by:

|A(x,z)| = √(∂M∂x )²+(∂M∂y )²+(∂M∂z )² 3.11

36

Where M = magnetic field

The analytical signal can be calculated with commonly available

computer software. The x and y derivatives can be calculated

directly from total magnetic field grid using a simple 3×3

filter, and the vertical gradient is routinely calculated using

FFT techniques.

Some of the properties of the analytic signal are

i. Its absolute value is symmetric it is independent to body

magnetization direction and ambient geomagnetic field and

only is relevant to body location.

ii. This quantity can be employed to causative body depth

estimation.

iii. Its maximum value lies over body directly

3.3.2 Source Parameter Imaging

The source parameter imaging method uses the local wave number

from an analytical signal to calculate depth to magnetic rocks.

The SPI function is a quick, easy, and powerful method for

calculating the depth of magnetic sources. SPI has the advantage

of producing a more complete set of coherent solution points and37

it is easier to use. The resulting images of SPI method can be

easily interpreted by someone who is an expert in the local

geology (Thurston and Smith, 1997). (Thurston and Smith, 1997)

estimates the depth from the local wave number of the analytical

signal.

The analytical signal A(x, z) is defined by Nabighian (1972) as:

A(x,z) = ∂M(x,z)∂x

−j ∂M(x,z)∂z

(3.12)

where M(x, z) is the magnitude of the anomalous total magnetic

field, j is the imaginary number, z and x are Cartesian

coordinates for the vertical direction and the horizontal

direction respectively. Nabighian (1972) showed that the

horizontal and vertical derivatives comprising the real and

imaginary parts of the 2D analytical signal are Hilbert

transformation pair

∂M(x,z)∂x

⇔ ∂M(x,z)∂z

(3.13)

38

Where ⇔ denotes a Hilbert transformation pair.

Thurston and Smith (1997) define the local wave number k (in

radian per ground unit) for this analytical signal to be

K= 2πf0

(3.14)

and

f0 = 12π

∂∂x

tan¯¹[ ∂M(x,Z)∂z

∂M(x,z)∂x ]

(3.15)

where f0 is cycles/ground unit and K is the wave number in radian

per ground unit.

K= ∂∂x

tan¯¹[ ∂M(x,Z)∂z

∂M(x,z)∂x ]

(3.16)

39

Nabighian (1972) gives the expression for the vertical and

horizontal gradient of a sloping contact model as

∂M(x,z)∂z

=2χMcsinβ·xcos(2I−β−90°)－hsin(2I－β－90°)

h²+x²

(3.17)

∂M(x,z)∂x

=2χMcsinβ·hcos(2I−β−90°)－xsin(2I－β－90°)

h²+x²

(3.18)

Where χ is the susceptibility contrast at the contact, M is the

magnitude of the earth’s magnetic field (the inducing field), c =

1-cos²isin²α, α is the angle between the positive x-axis and

magnetic north, i is the ambient-field inclination, tan I =

sini/cos8, β is the dip (measured from the positive x-axis), h is

the depth to the top of the contact and all trigonometric

arguments are in degrees. The coordinate system has been defined

40

such that the origin of the profile line (x = 0) is directly over

the edge.

Substituting equations 3.17 and 3.18 into 3.16 gives the wave

number for a contact profile as

Kmax = 1h

(3.19)

Depth(h)= 1

Kmax

(3.20)

K is wave number of the analytical signal

h is depth to the point of contact

using the concept of Hsu et al. (1996) for an analytic signal

comprising second-order derivatives of the total field, a second

wave number can also be generated.

From equation (3.19), it is evidently that wave number is

independent of susceptibility contrast, the dip of the source and

the inclination, declination, and the strength of the earth’s

magnetic field.

41

Equation 3.20 is the basics for SPI method (Adetona and Abu,

2013), it utilizes the relationship between source depth and the

local wavenumber of the observed field, which can be calculated

for any point within a grid of data through horizontal and

vertical gradients (Thurston and Smith, 1997). For vertical

contacts, the peaks of the local wave number define the inverse

of depth. The depth is displayed as an image (in colour

aggregate). Image processing of the source-parameter grids

enhances detail and provides maps that facilitate interpretation

by non specialists (Ojoh, 1992).

42

CHAPTER FOUR

INTERPRETATION OF RESULT

4.1. The Total Magnetic Intensity (TMI) Map of the Study Area and

Filtering Results

The total magnetic intensity map (figure 4.1) was produced with

computer software package (OASIS MONTAJ) used by the supervisor

for this project which is in color aggregate. The magnetic

intensity of the study area ranges from −691.5nT (minimum) to

400.8nT (maximum). Relatively high magnetic intensity was

observed in the central area compare to the rest of the study

area. The area is marked by both high and low magnetic

signatures, which could be attributed to several factors such as

variation in depth, difference in magnetic susceptibility,

difference in lithology, and degree of strike. Subsequent

interpretation under qualitative analysis will reveal more

information of each. The northern and the southern edge of the

study area have low magnetic signatures, which are generally

attributed to sedimentary areas. High magnetic intensity was

recorded at the southeast edge. The south west shows a lot of

activity, as they are dotted by mixtures of both high and low

43

magnetic structures with features that are characteristics of

surface to near surface structures such as outcrops.

4.2 Reduced to Equator

The TMI map was Reduced to Equator (figure 4.2) for the purpose

of removing the dependancy of the magnetic field on the angle of

inclination and as a result, the position and shape of the

anomaly was altered. The anomalies were observed to have been

shifted northward.

4.3 Horizontal Derivatives

The horizontal derivatives reveal contact locations that are

continuous, thin and straight. This map reveals structural

complexity such as faults inside the basement. For this purpose,

the horizontal derivatives were used to determine the locations

of physical property (magnetization) Boundaries. Result from

horizontal derivative DX (figure 4.3), intensifies more of the

structures towards the y-direction while the horizontal

derivative DY (figure 4.4) intensifies the structures towards the

x-direction. Short wave signatures are predominantly seen in the

NW and SE while long wave signatures are mostly found in the SW

and NE of portion the study area.

44

4.4 First vertical derivative

Result from the first vertical derivative,1VD (figure 4.5)

reveals more of the surface structures with short wavelength and

are of high frequency in occurrence. The southeast, northwest and

northeastern edge of the study area shows mixtures of high and

low magnetic susceptibility with features of lineation in value

and trend (black lines) that depicts fault line, fractures or

lithology contact. Long wave signatures are predominant in the

southwest region which reveals that there are deep magnetic

source within the study area typical of a sedimentary basin.

4.5 Results from Analytical method

The Oasis Montaj software uses the result from horizontal and

vertical derivatives to produce the amplitude values of the

observed anomaly (figure 4.6). The amplitude of the anomalies in

the study area ranges from 0.000nT/M to 2.730 nT/M. The map

reveals high amplitude anomalies at the northwest and southeast

portion of the study area while the southwestern region is

predominant with low amplitude anomalies. The northeast region is

mixed with both high and low amplitude anomalies. The high

amplitude anomaly accounts for low susceptibility while the high45

amplitudes accounts for high susceptibility within the study

area.

4.6 Source Parameter Imaging and Results.

.The Source Parameter Imaging (SPI) module from Oasis Montaj

software was applied to the TMI data of the study area; the SPI

statistics show a minimum depth of 95.380 meters and a maximum

depth of 8323.024 meters (figure 4.7). The highest depth can be

found at the southwestern part and relatively scattered around

southeast edge. Northwest and northeast shows relatively low

depth to basement rocks.

4.7 Correlation of results from Analytical Signal and SPI

The Analytical map and SPI map was gridded into six profiles

(figure 4.8 and figure 4.9 respectively). The two maps were

merged together and the six different profiles were drawn across

in such a way that they are perpendicular to the magnetic

structures within the area. The x and y coordinates on both the

SPI and analytical signal maps were obtained and the

corresponding values of depth and amplitude were equally

obtained. The result shows a remarkable contrast between the

46

amplitude response and depth response of an anomaly (figure 4.10

to 4.15).

Figure 4.10 is the amplitude response from analytical signal and

depth values from SPI obtained along profile 1. The analytical

signal graph shows the highest amplitude of 0.045nT/m at latitude

7°1'15'' and longitude 8°41'30'' were a shallow depth to magnetic

source of 166.7m was obtained. The SPI graph shows the maximum

depth to magnetic source on profile 1 as 3.33km which is located

at latitude 7˚41'36'' and longitude 8˚38'24'' and the amplitude

response to this depth was 0.03nT/m.




7˚6’24’’ and longitude 8˚46’36’’ were a shallow depth of 0.00m

was obtained on the SPI graph. The maximum depth on the SPI graph

was observed to be approximately 5.7km located at latitude

7˚1’48’’ and longitude 8˚55’ were an amplitude response of

0.00nT/m was obtained.

47






was observed to be approximately 2.33km located at latitude 7˚18'

and longitude 8˚41'12'' were an amplitude response of 0.00nT/m

was obtained.




7˚29’24’’ and longitude 8˚56’ were a shallow depth of 100m was

obtained on the SPI graph. The maximum depth on the SPI graph was

observed to be approximately 1.5km located at latitude 7˚23’36’’

and longitude 8˚56’ were an amplitude response of 0.00nT/m was

obtained.





48


was observed to be approximately 1.2km located at latitude

7˚27’36’’ and longitude 8˚50'24'' were an amplitude response of

0.00nT/m was obtained.






was observed to be approximately 4km located at latitude 7˚6’36’’

and longitude 8˚36’ were an amplitude response of 0.00nT/m was

obtained.

CHAPTER FIVE

CONCLUSION AND RECOMMENDATION

5.0 CONCLUSION

The Total magnetic intensity (TMI) data over Gboko area was

interpreted using Horizontal derivative, first vertical49

derivative (1VD), analytical signal and source parameter imaging

(SPI) for the purpose of geophysical interpretation of the buried

anomalies. From the results of our analysis in chapter 4 the

following conclusion can be arrived.

Result from the Horizontal derivative helps us to

identify regions of outcrops which signified by short

wavelength (high frequency) magnetic signatures. The

first vertical derivative helps to place our lineament

(in black lines) within the area they were discovered.

Which are lower mid portion, Northwest(NW) and

Northeast(NE) corner as shown on the map

Result from source parameter imaging (SPI) shows that the

minimum depth across the study area was 95.385meters and

the maximum depth to magnetic rock obtained was

8323meters.

Result from analytical signal shows that the amplitude

ranging from 0.03nT/m to 2.730nT/m represents the

outcrops magnetic rocks. Amplitude response ranging from

0.011nT/m to 0.03nT/m are region with magnetic rocks

50

intruding into sediment while the amplitude ranging from

0.00nT/m to 0.011nT/m are regions of high sedimentation.

Correlation between analytical signal and source

parameter imaging (SPI) reveals that the amplitude of

analytical signal is due to two main factors. The

vertical depth to the source rocks, the relative degree

of susceptibility region with high amplitude yield

shallow depth and region with low amplitude reveals a

reasonably high depth. Exceptional areas observed are

fractures and fault line where there exist a sharp drop

in amplitude response and depth.

5.2 RECOMMENDATION

The correlation between the depth results from SPI and the

amplitude response obtained from Analytical Signal reveals region

of high sedimentation, region of intrusions, regions of outcrops

and region of fault line around the study area. My

recommendations are as follows:

51

i. Building construction should not be carried out around

regions with fractures such as southeast and northwest of

the study area instead borehole drilling is recommended.

ii. Further research should be carried out around regions of

high sedimentation (southwest) as they are good potential

for hydrocarbon.

FIGURES

52

Figure 1.0: Showing the main division of the Earth, (Reeves 2005)

53

Figure 2: Geology map of the study area (adapted from the

Geological and Mineral Map of Nigeria, 2009, Nigerian Geological

Survey Agency).

54

7°00'

7°30'

9°00'

8°30'

Figure 4.1: TMI map of the Study Area.

55

Figure 4.2: TMI reduced to equator

56

Figure 4.3: horizontal derivative (DX) of the TMI map

57

Figure 4.4: Result of horizontal derivative (DY) of the TMI mapof the study area.

58

Figure 4.5: Result of First Vertical Derivative of TMI map

59

Figure 4.6: Analytical signal showing the amplitude of anomaly incolour aggregate.

60

Figure 4.7: Result from Source Parameter Imagine.

61

Figure 4.8: showing profile lines on the Analytical Signalresult.

62

Figure 4.9: showing profile lines on the SPI result

63

Figure 4.10: Grid analysis of profile one

Figure 4.11: Grid analysis of profile two

64

Figure 4.12: Grid analysis of profile three

Figure 4.13: Grid analysis of profile four

65

Figure 4.14: Grid analysis of profile five

Figure 4.15: Grid analysis of profile six

66

REFERENCES

Adighije, C., 1979, Gravity field of Benue Trough, Nigeria,

Nature 282 pp 199-201.

Adetona, A.A., and Abu, M., 2013, Estimating the Thickness of

Sedimentation within Lower Benue Basin and Upper Anambra

Basin, Nigeria, Using Both Spectral Depth Determination and

Source Parameter Imaging . Hindawi Publishing Corporation ISRN

Geophysics Volume Article ID 124706, pp 1-10

Agagu, O. K., and Adighije, C. 1983, Tectonic and sedimentation

framework of the Lower Benue Trough, southeastern

Nigeria. Journal of African Earth Sciences 1, pp. 267 - 274.

Agagu, O. K., Fayose, E. A., and Petters, S.W., 1985,

Stratigraphy and sedimentation in the Senonian Anambra

basin of eastern Nigeria. Nigerian Journal of Mining and Geology

22, pp. 377 - 385.

Ajakaiye D.E., and Burke, A., 1973, Bouguer gravity map of

Nigeria, Tectonophysics 16 103-115.

67

Akande S.O., Ojo J.O., Adekeye O.A., Egenhoff S.O., Obaje N.G.,

Erdtmann B.D., 2011 Petroleum Technology Development Journal 1 pp.

3–13.

Allix P., 1987, Le bassin d'Anambra: essai du caracterisation de

l' évolution tectono -sedimentaire au Crétacé supérieur.

Bulletin des Centres de Recherches Exploration -Production Elf Aquitaine 11, pp. 158

- 159.

Bhattacharya B.K., 1966, continuous spectrum of the total magnetic fieldanomaly due to a rectangular prismatic body, Geophysics vol 31 pg 97-121

Burke K.C., Dessauvagie, T.F.J., and Whiteman, A.J., 1970,

Geological history of the Benue Valley and adjacent areas,

in: African Geology, Ibadan.

Burke K,. Dessauvagie T.F.J and Whiteman A.J., 1971, Opening of

the Gulf of Guinea and geological history of the Benue

Depression and Niger Delta, Nature Phys. Sci. 233

pg51-55.

Burke, K., and Whiteman, A.J., 1973, Uplift, rifting and the

break-up of Africa, in: Implications of Continental

Drift to the Earth Sciences, Academic Press, London, pg

735-755.

68

Carter, J.D., Barber, W., and Tait, E.A., 1963, the geology of

parts of Adamawa, Bauchi and Bornu Provinces in

northeastern Nigeria, Bull. Geol. Surv. Nigeria 30 pp 109.

Cratchley, C.R., and Jones G.P., 1965, An interpretation of the geology

and gravity anomalies of the Benue Valley, Nigeria, Overseas Geol.

Surv. Geophys. Paper No.1 26 pp.

Colin, R., 2005, Aeromagnetic surveys principles, practices andinterpretation pg 1-9

David, I., Marius, N.U., 2013, interpretation of Aeromagneticanomalies over some parts of lower Benue trough usingspectral analysis techniques pg 153

Dessauvagie, T.F.J., and Whiteman, A.J., 1972, eds. University of

Ibadan, Ibadan, pg187-205.

Dessauvagie, T.F.J., 1975, A Geological Map of Nigeria, Scale 1 :

1000000, (Nigerian Mining, Geological and Metallurgical

Society,).

Freeth, S.J., 1978, Tectonic activity in West Africa and the Gulf

of Guinea since Jurassic times - an explanation based on

138 membrane tectonics, Earth Planet. Sci. Lett. 38, 298-300.

Freeth, S.J, 1978, A model for tectonic activity in West Africa

and the Gulf of Guinea during the last 90 m.y. based on

membrane tectonics, Geol. Rundsch. 67 pg 675- 688.

69

Grant, N.K., 1971,South Atlantic, Benue trough and Gulf of Guinea

Cretaceous triple junction, Geol. Soc. Am. Bull. 82 pg 2295-

2298.

Grant, F.S., Dodds, J., 1972, MAGMET FFT processing system

development notes, Paterson Grant and Watson Limited.

Hsu, N. C., Herman, J. R., Bhartia, P. K., Seftor, C. J., Torres,

O., Thompson, A. M.,

Gleason, J. F., Eck, T. F., & Holben, B. N., 1996, Detection of

biomass burning smoke from TOMS measurements. Geophys.

Res. Lett., 23, 745– 748.

Mendona, C.A., and Silva, B.C., 1993, A stable truncated series

approximation of the reduction to pole operator:

Geophysics 58, 1084-1090

Murat, R.C., 1972, Stratigraphy and Paleogeography of the

Cretaceous and Lower Tertiary in South- Eastern Nigeria. In:

Dessauvagie T. F. J., Whiteman A. J. (Eds), African Geology.

Ibadan University Press, pp 251–266.

Nwachukwu, S. O., 1972, The tectonic evolution of the southern

portion of the Benue Trough, Nigeria, Geol. Mag. 109, pg

411-419.

70

Nwachukwu, S. O., 1972, Geological Magazine 109, pp. 411 – 419.

Nabighian, M. N., 1972, The analytic signal of two dimensional

magnetic bodies with polygonal cross-section.its properties

and use for automated anomaly interpretation.Geophysics, 37, 507-

517.

Nabighian, M. N. 1984, towards the three-dimensional automatic

interpretation of potential field data via generalized Hilbert

transforms: Fundamental relations: Geophysics, pp 957-966.

Najime T, 2011, Depositional framework and Cretaceous

stratigraphy of the Gboko Area Lower Benue Trough, Nigeria.

Pg3-10.

Nwugha, V.N., Nwagbara, J.O.,Okorie, J.O., Nokereke, C., andChinemelu, E.S., 2012 Geophysical estimate of depth of someanomalous geologic features in parts of lower Benue troughpg 517-519

Ojoh, K. A., (1990). Cretaceous geodynamic evolution of the

southern part of the Benue Trough (Nigeria) in the

equatorial domain of the South Atlantic; Basin analysis and

Paleo- oceonography. Bulletin des Centres de Recherches Exploration-

Production. Elf - Aquitaine 14, pp. 419 442.

Ojoh, K.A., 1992, The Southern part of the Benue Trough (Nigeria)

Cretaceous stratigraphy, basin analysis, paleooceanography 71

and geodynamic evolution in the equatorial domain of the

South Atlantic. NAPE Bulletin 7, pp. 131–152.

Olade, M.A., 1975, Evolution of Nigeria's Benue Trough,

(Aulacogen); a tectonic model. Geological Magazine 112, pp. 575

581.

Olade, M.A., 1978, Early Cretaceous basalt volcanism and initial

continental rifting in Benue Trough, Nigeria, Nature 273,

458-459.

Petters, S.W., and Ekweozor, C.M., 1982, Petroleum geology of the

Benue Trough and southeastern Chad Basin, Nigeria. Bulletin

American Association of Petroleum Geologists 66, pp. 1141-

1149.

Reyment, R. A., and Mörner, N. A., 1977, Cretaceous

transgressions and regressions examplied by the South

Atlantic. Paleontological Society of Japan, Special Paper 1, pp. 247-261.

Reyment, R. A., 1965, Aspects of the Geology of Nigeria. Ibadan

University Press, 133 p11-25.

Smith, R.S., Thurston, J.B., Dai Ting-Fan Ian, N.M., 1998,

iSPITM- the improved source parameter imaging

method. Geophysical prospecting, 46, 141-151.

72

Tijani M. N., Loehnert., E. P., Uma, K.O., 1997, Journal of African

Earth Sciences 23, pp. 237- 252.

Thurston, J. B., and Smith, R.S., 1997, Automatic conversion of

magnetic data to depth, dip, and susceptibility contrast using

the SPITM method. Geophysics, 62, 807- 813.

Ugbor., D., and Okeke, N., 2010, Geophysical investigation in thelower Benue trough using the Gravity method pg 1-8

Uzuakpunwa, A.B., 1974, The Abakaliki pyroclastics, Eastern

Nigeria: new age and tectonic implications, Geol. Mag. 111

pg 65-70.

Wright, J.B., 1976, Origins of the Benue Trough - a criticnnal

review, in: Geology of Nigeria, C.A. Kogbe, ed. (Elizabethan

Publishing Co., Lagos) pg 309-317.

Zaborski, P.M., 2000, The Cretaceous and Paleocene transgressions

in Nigeria and Niger. Journal of Mining and Geology 26, pp. 153 –

170

73

interpretation of aeromagnetic data over gboko using spi and analytical method

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