Integration of the Gravity and Sounding Resistivity Methods to Study the Subsurface Geology and Structures in the Area North of the White Nile State, Sudan

7/30/2019 Integration of the Gravity and Sounding Resistivity Methods to Study the Subsurface Geology and Structures in the Area North of the White Nile State, Sudan

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2012

University of Khartoum

Fa culty of Science

Depar tment of Geology


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University of Khar toum

Faculty of Science

Department of Geology

Integration of The Gravity and Sounding Resistivity Methods to

Study The Subsurface Geology and Structures in The Area North

of The White Nile State, Sudan

Prepared by

Rami Kamal Abdel Rahman IbrahimB.Sc. in Geophysics, Cairo University, Egypt

E-Mail: [email protected]


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Abstract

An electrical resistivity survey was carried out in the area north of the

White Nile state, Sudan, between latitudes 14.5o 15o N, and longitudes 32o32.35

oE. About 1610 Km

2of survey area is covered.

The present field data were compiled with available resistivity data

(Hassan, 2009) and previously processed gravity data (Mohammed, 1997 and

Farwa, 1978) in the surveyed area.

The area is covered by extensive sand dunes and Qoz sands except for afew scattered outcrops. This blanket renders the geological interpretation difficult.

This problem was the main reason for using the geophysical methods as the main

tools for sounding the subsurface geology.

A residual gravity anomaly map, and structural contour mapare produced

for the study area. The negative residual anomalies are related to the upper

Cretaceous sediments filling all depressions in the Basement Complex surface

while the positive residuals are attributed to the relatively shallow or outcropping

Basement Complex rocks.


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acknoledgment

I would like to express my great thanks to Allah, for his inspiration and

supporting in difficult times.

I am indebted to my family with deep gratitude and regards for their

understanding and unlimited supporting.

his keen guidance and supervision.

My thanks extended to Dr. Ibrahim Abdu Mohammed, Chairman of

Geology Department, Faculty of Science, University of Khartoum for his constant

encouragements and for the help he offered to us to complete this present work.

Special thanks to Dr . Abdall a Gumaa Farwahis for the help he offered

through conducting this work.

I would like to express my deep thanks to all teaching staff in the Geology

Department-University of Khartoum, the staff of the Geological Research

Authority of the Sudan (GRAS), and Non-Nile Water Cooperation (NNWC) forthey co-operation in this work.

Also I would to express my thanks to people of Al-Alaga village for their

Also, I would thanksmy supervisor, Dr . Mohammed El Mahdi Siddigfor


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Contents

Chapter 1: Introduction . 11.1Overview . 2

1.2The Study area .. 2

1.2.1Location . 21.2.2Accessibility .. 3

1.2.3Population .. 3

1.2.3Population .. 3

1.3.1Topography 31.3.2Vegetation . 4

1.3.3Climate . 4

1.4Previous Works . 4

1.5Present Work 5Chapter 2: Regional Geology ... 8

2.1- Introduction .. 9

2.2 - Basement Complex Rocks (Pre-Cambrianlower Paleozoic) 92.3- Nubian Sandstone Formation (Mesozoic) . 13

2.4 - Tertiary Volcanics 14

2.5Umm Ruwaba Formation (Quaternary) ... 142.6Gezira Formation (Quaternary) ... 14

2.5 - Superficial Deposits . 15

2.6Structures . 16

Chapter 3: Regional Gravity Method ... 17

3.1Introduction 183.2 - Basics of the Gravity Method .. 19

3.2.1Drift Correction 193.2.2 Gravity Data Reduction 19


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4.5 Limitations of the resistivity method .. 43

4.6 Data Interpretation .. 43

4.6.1 Qualitative Interpretation . 434.6.1.1 Resistivity Curve Type . 434.6.1.2 Pseudo-section .. 44

4.6.2 Quantitative Interpretation ...... 47

4.6.2.1 True Resistivity determination . 474.6.2.2 Geo-electrical Section ...... 50

4.7 Summary .57

Chapter 5: Discussion and Conclusion .... 58

5.1 General 595.2 Results of The Gravity and Sounding Resistivity Methods 62

5.3 Geology and Structures ... 62

5.4 Tectonic Setting ... 685.5 Conclusion and Recommendations . 70

References 71

Appendix A- Gravity Data

Appendix B- Resistivity Data


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List of figures

Figure 1.1: Location of the study area 6Figure 1.2: The topographic map of the study area 7

Figure 2.1: Show the geological units in the study area and surrounding, based on

the geological map of the Sudan 1981 10Figure 2.2: Show a contour map for a preliminary depth of the Basement Complex

according to the information of the boreholes in table 2.1 . 12

Figure 3.1: Gravimeter drift curve constructed from repeated readings at base

station. 19Figure 3.2: Bouguer anomaly map of the study area.. 24

Figure 3.3: Profile I-I. (A) Observed (Bouguer) and regional gravity. (B) Residual

and modified gravity. (C) Density model. (D) Geological section.. 28

Figure 3.4: Profile II-II. (A) Observed (Bouguer) and regional gravity. (B)Residual and modified gravity. (C) Density model. (D) Geological section 29

Figure 3.5: Profile III-III. (A) Observed (Bouguer) andregional gravity. (B)

Residual and modified gravity. (C) Density model. (D) Geological section... 30Figure 3.6: Regional anomaly map of the study area. 32

Figure 3.7: Residual anomaly map of the study area.. 33

Figure 4.1:. Illustrate the relationship between the resistivity and resistance. 36Figure 4.2: Show each electrode array with its apparent resistivity equation. (a)

Wenner array, (b) Schlumberger array, and (c) dipole-dipole array 38

Figure 4.3: Shows the electrode locations during the VES survey by using

Schlumberger array, and resulted curve.. 39

Figure 4.4: Shows the electrode locations during the HEP survey by using Wennerarray, and resulted curve... 40

Figure 4.5: Shows the electrode locations during the ERT survey by using dipole-dipole array.. 40


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Figure 5.3: Structural contour map of the study area, describes the depth to the

Basement Complex surface with associated structures 63

Figure 5.4: Profile X-X. (A) Residual Gravity anomaly. (B) Geological section... 65Figure 5.5: Profile Y-Y. (A) Residual Gravity anomaly. (B) Geological section... 66Figure 5.6: Profile Z-Z. (A) Residual Gravity anomaly. (B) Geological section... 67

Figure 5.7: Tectonic model of the West and Central African Rift System (WCARS)

from Fairhead (1988) ... 69

List of tables

Table 2.1: The boreholes in the area and surrounding which reach to the Basement

Complex.. 11Table 4.1: Shows the information at each VES in the study area.. 48

Table 4.2: List of Boreholes did not reach the basement Complex . 50

Table 4.3: Resistivity of the various rock and sediments. 50

List of abbreviations

DC = Direct Current.

Fm = Formation.


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Chapter One

Introduction

An electrical resistivity survey was carried out in the area north of the White Nile

state between J. Helbi and Eid Umm Esh region during the period between 8th

and 15th

of

April 2012. About 1610 Km2 of survey area is covered. The present field data were

compiled with available resistivity data and previously obtained gravity data in the

surveyed area.

The surveyed region is covered by extensive sand sheets and Qoz sediments. The

sand cover is expected to be the general problem, which masks the subsurface geology

information. Scattered Basement complex outcrops or Basement shallows are recognized

within and around the area.

Structurally the area lies marginal to Khartoum basin in the east, and to Bagabag

basin in the northwest. Presence of other basins or their extensions within the area is still

under investigation. The area was affected by many structural movements, which resulted

in the formation of a series of grabens and horsts.

Integration of the electrical and gravity method with other geological information

proved to be effective in delineating the subsurface geology. Gravity is particularly

ff i i i fl h k i d f bl i

1.1- Overview:


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1.2.2Accessibility:

The area is accessible via a paved road from Jebel Aulia. The other parts are difficultto traverse because the presence of the sand dunes.

1.2.3Population:

The majority of the inhabitants of the area (west of the White Nile), belongs to the

Kawahla group. However, the region is known as Dar Hassaniya. Other small tribes also

live in the area. Generally the people depend heavily for their living on irrigation

schemes, rain-fed cultivation and livestock. They also practice trade between their

villages and Khartoum State.

1.3Physiography:

1.3.1

Topography:

The study area is generally flat, which slopes gently to the White Nile River with

low gradients that rarely exceed 1 meter per kilometer (Mohammed 1997). The west of

the White Nile is characterized by three landscapes:

o The flat clay plain.o Qoz (sand dune): The areas of Qoz are slightly undulated and form low

rises above the clay plain, (figure 1.1).

o Isolated inselbergs (jebels), (figure 2.1 in chapter 2).


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1.3.2Vegetation:

The vegetation cover is poor in the region, and becomes relatively densersouthward, obviously with the increase of amount of the rainfall. Trees, thorny shrubs

and acacia are wide spread in the area whereas dry grasses are confined to the valleys.

1.3.3Climate:

The climate of the region varies from arid to semi-arid with an average annual

rainfall of 200 mm (Davis, 1985). The rainy season occurs between June and September,

while, the dry season occurs between November to April or early May. The temperature

varies considerably with the variation of the seasons. The mean annual temperature is

29oC with the minimum and maximum temperature values reaching 15

oC in winter and

42oC in summer.

1.4

Previous Works:

The geological information of the area is masked by extensive sand cover.

Therefore areas the classical geological mapping is not efficient. This leads to the

previous researches to restrict their works to sub-surface geological mapping utilizing

geophysical methods as well as borehole data.

o Mitwali (1969), carried out regional gravity measurements in northeast KordofanState. He interpreted the negative anomalies observed to be associated with the

fault bounded rift structures that form Bara Basin. The sediments in the basin

reach thickness 2000 m


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clusters. This feature is interpreted to be resulted from crustal thinning coupled

with passive mantle uplift.

o Ibrahim (1993), investigated several basins north of the Central African ShearZone (CASZ) in the Sudan, by compilation of all available gravity data from

central Africa including Sudan.

o Mohammed (1997), executed a regional gravity survey in the area west of theWhite Nile along its extension from Kartoum in the north to Ed-dueim in the

south. He produced a bouguer anomaly map of scale 1/50000, and interpreted

nine selected profiles which pass over anomalous zones in the area. He

investigated several basins in the area locally named Sheikh Sidig, Wad El-

Bakhit, and Mugeriant.

o Hassan (2009), applied gravity and resistivity methods in the area west of theWhite Nile between latitudes 14.5

o - 15.1

oN and longitudes 31.8

o - 32.4

oE. He

made a structural map of the area, and reveals three sedimentary basins, which

interpreted to be fault-controlled. These basins are named, Shikh Sidig, Umm

Andraba, and Alaga.

o Chevron Over Seas Petroleum in 1975 started hydrocarbon exploration in thewest and southwest of the Sudan, starting with the acquisition of aeromagnetic

data followed by gravity and seismic surveys. As the result of these surveys,

several basins and rifts were delineated.

o A consortium of oil companies has obtained aeromagnetic gravity, and seismicdata of central Sudan centered about Khartoum in the Nile drainage basin. Several

Structural features, interpreted as rifts (White and Blue Niles Rifts).

1 5 Present Work:


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Chapter Two

Regional Geology

2.1- Introduction:

General treatments of the geology of the Sudan have been presented by Andrew(1948), Whiteman (1971), and Vail (1978 and 1982). Figure 2.1, illustrates the general

geological map of the area between latitudes 14o 16

oN and longitudes 30

o 34

oE

principal geologic units (figure 2.1) encountered in the study area and the surrounding are

listed from oldest to youngest as follows:

1. Basement Complex Rocks (Pre-Cambrianlower Paleozoic).2. Nubian Sandstone Formation (Mesozoic).

5. Gezira Formation (Quaternary).6. Superficial Deposits.

2.2 - Basement Complex Rocks (Pre-Cambrianlower Paleozoic):

extracted from the geological map of the Sudan (GRAS 1981) (scale 1:2,000,000). The

4. Umm Ruwaba Formation (Quaternary).3. Volcanics, mainly basalts(Tertiary).


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There are some boreholes drilled mainly for water supply purposes in the area by

Geological Research Authority of the Sudan (GRAS), and Non-Nile Water Cooperation

(NNWC). The information about these wells is collected from Ground Water Directorateand during the reconnaissance geological survey carried out during these present work.

Table 2.1 shows some boreholes location and the depth to the Basement Complex.


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BH no. NameLongitude

in degree

Latitude

in degree

Depth to the

BC in meter

BH 1 EL HUNO 31.6167 14.4167 137

BH 2 MUGRIANT 31.6500 14.4500 178

BH 3 AL ALAGA 32.16 14.757 97

BH 4 EL BIHAER 31.7667 14.1167 105

BH 5 HAGIBA 31.7833 14.7000 172

BH 6 EL HUMRAYA EL MAGDIA 31.8333 14.4667 107BH 7 UM ANDRABA 31.8833 15.2000 117

BH 8 EL SHIGIG 31.9000 15.0333 135

BH 9 ESSYAL 32.0000 14.5000 141

BH 10 EL DUEIM 32.0056 14.0006 78

BH 11 EL GETAINA 32.0125 14.8333 69

BH 12 AWLAD EL EBIAD 32.0167 14.2833 97

BH 13 EL SILEIK 32.0333 14.3333 107

BH 14 UMM ESHUSHAT 32.0333 14.7917 17

BH 15 EL HUWIDA 32.0333 15.2667 25

BH 16 GOZ EL BIED 32.1333 14.4000 199

BH 17 UMM NALA 32.1333 14.9167 108

BH 18 EL SHETEIB 32.1833 14.3833 93

BH 19 EL SHAWAF 32.2000 14.7333 72

BH 20 HAFEIR ELFAKI ABEDELB 32 2000 14 8167 66

Table 2.1

The boreholes in thearea and surroundingwhich reach to the

Basement Complex.


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Figure 2.2 show a contour map for the depth of the Basement Complex according

to the table 2.1. There are some deep Basement Complex rocks found in the east and the

west of the map nearly at 180 m in depth. There are some shallow depths in north andcenter of the map where the depth is nearly 20 - 30 m. Also there are some shallow to

medium depths in the south nearly equal 80 m. From that we can say there was uplifting

for the basement Complex in El-Huwida area (BH 15) in the center, Goz El Bied area

(BH 16) in the north, and Wad El Hedeba (BH 26) in NE of the map. Also there is little

uplifting for the basement Complex in El Getaina area (BH 11) in the southe of the map.

Generally there is a strong indication to present a dip-slip fault in the in the north of the

map between El-Schtab area (BH 24) the down thrownand the Goz El Bied area (BH

16) and El-Terasab (BH 28). The maximum depth recoded is in Abu Agaga (BH 23) in

the center of the map where the depth of B.C is about 241 m

2.3- Nubian Sandstone Formation (Mesozoic):

This Formation is made from unmetamorphoesd bedded of sedimentary rocks

which rest unconformably on Basement Complex rocks. This formation covers 28% of

the surface area of Sudan and continuous to Egypt, Chad, and Libya. The Nubian

Sandstone Formation in Sudan is defined to include conglomerates, grits, sandstones,

sandy mudstones, and mudstones (Upper cretaceous).

A typical lithology classification of Nubian Sandstone Formation is given by

Kheiralla (1966) for Khartoum - Shendi, which the beds are horizontal or gently dipping.

The following lithological units were established by Kheiralla:


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According to Abdel Salam (1966) and Whiteman (1971), the Geaira Formation is

composed of three lithological members; these are listed from oldest to youngest:

1.Mongataa member: It is predominantly made of coarse arkosic gravels, sands,and clayey grit showing variable thickness and fining upward. the average

thickness is 9 m.

2. Lower sandy member: It is mainly made of sands accompanied with gravel, silt,and clayey lenses. Gravel lenses vary in thickness from few centimeters to over

30 cm. The thickness of this member vary between 20 to 58 m with average of 35

m3. Upper clay member Gezira clay: It is mainly made of clays with occasional

patches of sand.

lower Gezira Formation. An age of Oligocene Miocene is given for the upper Gezira

Formation, while an age of Mastrichian Paleocene is assigned to the lower Gezira

Formation. It consists predominantly of sand and clay interbeds, and occasionallimestone and tuffaceous material which occur near to the top of the member. The clays

are light grey to reddish brown. The sands are loose, coarse to medium grained and

moderately sorted.

Umm Rawaba formation and Gezira formation are important because:

1) They blanket much Basement Complex and Nubian Sandstone.2) They make a good agricultural soil.3) Are source of ground-water

Awad (1994) added to this succession a fourth basal Member at Wad madani


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2.6Structures:The structure of the area is not complicated and it can not be detected from the

surface, this is because the area is covered by loose sand. However, geological and

geophysical studies in the area revealed that the rocks have been subjected to faulting. In

the southwest of the Khartoum, systems of NW SE, N-S, and E-W fault strikes exist.

These fault systems possibly resulted from tectonic movements.

According to Ibrahim et.al (1996), structurally the study area lies between

Khartoum basin (Blue Nile Rift) in the east, Bagbag in the northwest and Kosti (WhiteNile Rift) in the southwest. These basins mark NW trends. The two former basins are

truncated at the north east by the ENE Central African Shear Zone CASZ which is

suggested to be boarder zone of deformation. This Zone crosses Bagbag basin and pass

north of the study area.

According to Farwa (1978), the east of the area, at Jebel Aulia, a major NW

trending fault is observed cutting the Nubian Sandstone Formation near the Jebel Aulia

dam, with the NE block thrown down more than 1000 m.

Mula et.al (1993), showed that western part of the White Nile area consists of a

system of horst and graben structures striking largely in NW-SE direction.


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3.2 - Basics of the Gravity Method:

3.2.1

Drift Correction:

Correction for instrumental drift is based on repeated readings at a base station at

recorded times throughout the day. The meter reading is plotted against time and drift is

assumed to be linear between consecutive base readings. The drift correction at time (t) is

(d), which is subtracted from the observed value (figure 3.1).

3.2.2Gravity Data Reduction:

Before the results of a gravity survey can be interpreted it is necessary to correct

for all variations in the Earthsgravitational field which do not result from the differencesof density in the underlying rocks. During the regional survey the sea-level is usually the

most convenient datum level, but during the detailed survey the datum will be the

elevation of the base station

Figure 3.1: Gravimeter drift curve

constructed from repeated

readings at base station. The drift

correction to be subtracted from

a reading taken at time (t) is (d).


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thickness equal to the elevation difference (h) between the datum and the

station. The BC is negative for an observation point above datum .The

elevation (h) is in meters and the density () is in gm/cm3

.

BC = 0.04191 h ( in mGal/m) eq. 3.5

2) Terr ain Correction:this correction allows for surface irregularities in the vicinityof the field station e.g. hill rising above the gravity station or valleys below it.

There are several graphical methods for calculating terrain corrections, all of them

require good topographical maps of the area extending if possible considerably

beyond the survey grid (within which the elevations are known more

precisely).This correction was not performed in the study area because the

surveyed area is relatively flat, see figure 1.2 in chapter 1.

3) Latitude Correction:gravity increases with latitude to be maximum at the polesand minimum at the equator because the non-spherical shape of the Earth and its

rotation. The variation of the gravity of the Earth as expressed by the International

Gravity Formula (INGF) 1967. is the geographical latitude in degree.

g= 978031.85 (1+5.278895 X 10-3

sin2+ 2.3462 X 10

-5sin

4) in mGal .. eq. 3.6

3.3Bouguer Anomaly:

When all preceding corrections are applied, simple Bouguer gravity anomaly for

the station are obtained according to the formula:

gB= gobs+ ge- g .. eq. 3.7


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The edges of a body will tend to lie under inflection points on the gravity profile.In this thesis the Bouguer anomaly map (figure 3.3) is produced by using an oldBouguer data carried out by Mohammed (1997) compiled with Farwa gravity data (1978)

in the area between latitudes 14o 15.3

oN and longitudes 31. 8

o 32.6

oE, under next

conditions:

o The elevation factor = 0.1967 mGal /m.o Average crustal density = 2.67 g /cc.o Normal gravity calculated using (INGF 1967).o The main base-station is at Geology Department, University of Khartoum, with

absolute gravity equal 978303.38 mGal

3.4Gravity Data Interpretation:

3.4.1Qualitative Interpretation:

The Qualitative interpretation of the gravity method is describing and explainingthe anomalies in the form of geological and geophysical knowledge, geological

structures, tectonic boundaries and density contrast from the masses. The common

situations that give rise to gravity anomalies in the area are:

o Topography of the Moho (changes in crustal thickness), which does not existhere.

oDensity variation within the Basement rocks.

o Topography of the interface between Basement and overlying sediments.o Density variation within the sediments.


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o The second zone is in the middle of the map which forms an elliptical shape, andthe gravity varied in range from -20 to -16 mGal with amplitude 4 mGal. The

dimension of this pattern is 17.6 km in NW-SE trend, and 10.3 km in NE-SWtrend. This pattern indicates shallow basement Complex (figure 3.2). The

borehole in this zone BH 26 and BH 28 reach the Basement Complex at depths 66

m and 158 respectively.

o The third zone is near to the second zone to the west direction of it. The gravityvaried in range from -18 to -20 mGal with amplitude 2 mGal. This zone has semi-

elliptical shape with dimension 30.8 km in N-S trend, and 14.7 km in E-W trend.

During the reconnaissance, the author found that there are an outcrop of Basement

Complex near to Umm Eshushat village and this outcrop located in this zone

"marked by purple star in figure 3.3" with gravity anomaly nearly -19 mGal

(figure 3.2).

o The fourth zone is located in the south western part of the map in which thegravity values gradually increases to the west direction from -28 to -24 mGal. The

borehole BH 6 is close to this zone and the depth of Basement Complex at this

borehole is 107 m (figure 3.2).

o The fifth zone is in the southern part of the map and the gravity values increasesin south direction from -26 to -22 mGal. This pattern indicates to presence of

shallow Basement Complex. The borehole BH 22 is in the middle of this zone,

and the depth of the Basement Complex is 106 m (figure 3.2).

The Bouguer anomaly map (figure 3.2), the Bouguer anomaly values are low along seven

zones described from top to bottom of the map:

The first zone is in the north western part of the map right at the corner, and the


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The fourth zone is in the east of the map and has a spherical shape, the gravityvaried in range from -28 to -34 mGal with amplitude 4 mGal. The dimension of

this pattern is 7.6 km in N-S trend, and 6.1 km in E-W trend. This patternindicates to presence of a basin (figure 3.2).

The fifth zone is in the middle of the map which formed an elliptical shape, thegravity values varied in range from -42 to -56 mGal with amplitude 14 mGal. The

dimension of this pattern is 26.4 km in E-W trend, and 16.2 km in N-S trend. This

pattern indicates to presence of a basin (figure 3.2).

The sixth zone is in the south eastern part of the map which formed a sphericalshape, the gravity values varied in range from -44 to -54 mGal with amplitude 10

mGal. The dimension of this pattern is 35.2 km in NE-SW trend, and 29.2 km in

NW-SE trend. It is regionally trend in east direction. This pattern indicates to

presences a basin. There is a borehole in this zone BH 29 which reaches the B.C

at depth 200 m (figure 3.2).

Seventh zone is in the south western part of the map which formed a sphericalshape, the gravity values varied in range from -30 to -34 mGal with amplitude 4

mGal. The dimension of this pattern is 17.6 km in N-S trend, and 16.1 km in E-W

trend. This zone is close to Jebel Arshkol, the distance from the Jebel and the

center of the minimum anomaly is nearly 7.3 km. The borehole BH 10 is near to

this zone which the depth of the B.C is 78 m (figure 3.2).

There are five steep gravity gradients also noted in this map described from up to down

of the map:

The first steep zone is in the north eastern part of the map with a N-S trend, Thegravity values varied in range from -24 to -36 mGal. Its slope is nearly1.9


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Mula, 1971). The residual gravity at each Basement Complex outcrop is zero.

( = - 0.45 gm/cc). The observed (Bouguer), regional, and residual gravity along profile

I-I are shown in figure 3.3 (A) & (B), along profile II-II are in figure 3.4 (A) & (B), andalong profile III-III are in figure 3.5 (A) & (B).

3.4.3Quantitative Interpretation (Modeling):

The quantitative interpretation is an inversion, which gives the nature, depth and

extension of the causative body. It is of great importance to estimate the densities of the

subsurface rocks before one can postulate their structure.

The interpretation can be direct or in direct. The direct (inverse) interpretationis

determining the possible mass distribution directly from the observed gravity data. The

indirect (forward) interpretationis modeling the causative body based on the geological

and structural parameters of the area.

A model is proposed and the theoretical anomaly of this model is compared with

the observed gravity. The geometry of the model can be modified until a good fit between

the observed and calculated gravity results. The model that gives a good match to the

observed anomaly is considered.

Gravmodeler is optimized to model Bouguer anomalies with bodies of various

densities embedded within a homogenous background. At each observation point, the

gravity response of a single body can be computed based on:

1) The difference between the density of the body and the background density.


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fitted by using the boreholes tapped the Basement Complex. Figure 3.3 (B) shows

the difference between the residual gravity calculated by the eq. 3.8 and the

theoretical gravity selected by the software. Figure 3.3 (C) shows the densitymodel for this profile, as shown, there is a decreasing in depth toward the SE

direction until 57 km then increased until has a shallow depth. Figure 3.3 (D)

show the suggested geological section along the profile on the basis of the density

model, in this section there are four faults detected all faults have down-thrown in

the south eastern direction except the last one (one the right-hand side) where the

down thrown is in the north western direction. First three faults show a domino

style, and the maximum depression detected has depth about 800 m. Note that,

since the regional - residual separation was applied on the profile and ignored the

surrounded structures, the Basement Complex outcrop near to this profile did not

appear on the model, and this is one of the most disadvantage of this type of

separation.

o Profile II -II:ThisProfile has NE-SW trend, and starts from coordinate 32.55oE& 15.25

oN, and passing trough boreholes BH 30 (WAD GAR EL NOBI) and BH

17 (UMM NALA) and terminates at coordinate 32.07oE & 14.87oN with length

about 58.3 km (figure 3.2). As profile I-I' the separation was by profile (figure 3.4

A, and B). The geological section (figure 3.4 D) is produced from the density

model (figure 3.4 C) and shows that there are four faults, the first and fourth faults

have down thrown in the north eastern direction, while the second and the third

faults have down thrown in the south western direction. There are two depression

appear in this section, first one is at the front of the profile it is represent to oneside of a basin and the maximum depth detected along this profile is about 1000

m. The second one is at 40 km which has maximum depth about 400 m. The

B t C l t b h ll t th d f th fil Th


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Ohms Law is V = IR .. eq. 4.1

Where (V) is the voltage drop or potential difference from one end of the resistor toanother, (R) is the resistance, (I) is the current. If the resistivity of the conducting cylinder

having a length (L) and cross-section area (A), then the resistivity is expressed as:

=

. eq. 4.2

The unit of the resistivity is .m.

4.2.1 Apparent Resistivity (a):

The apparent resistivity of a layered earth is defined as the resistivity of

homogeneous Earth in multi layered case, the layer resistivities can be derived from theapparent resistivity measured as a function of the current carrying electrode spacing

multiplied by the penetration depth of the current. The apparent resistivity calculated is

not the true resistivity of the subsurface but is the resistivity of a homogeneous groundwhich will give the same voltage and current values for the same electrode arrangements.

The apparent resistivity will equal the true resistivity only in case of homogeneous

subsurface.

By measuring (V) and (I) and knowing the electrode configuration, we can

obtain an apparent resistivity value (a) defined as the following equation:

a = K

.. eq. 4.3


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4.4 Resistivity Data Acquisition:

The resistivity instrument used during the survey is ABEM SAS1000, which it isable to be used during the self-potential and induced polarized measurements (figure 4.6).

Also during the survey we used many electrodes at least 4 electrodes made from steel,

aluminum, or brass and named in sequence as A, M, N, and B.

A and B are used to inject the current in the subsurface, while M and N are used

to detect the potential difference between them.

The configuration used is Schlumberger array to applying Vertical ElectricalSounding (VES) at 16 points named from VES 1 to VES 16 distributed on the study

area which they locations selected by using GPS to be compiled to VESs from previous

work (31 VESs) carried out in 2009 by B. Hassan for his M.Sc. degree in geophysics

named from VB 1 to VB 31. From this distribution the author choose 5 profiles to

cover the study area and apply the interpretation on them (figure 4.7).


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4.5Limitations of the resistivity method:

Resistivity surveying is an efficient method for delineating shallow layeredsequences or vertical discontinuities involving changes of resistivity. It does, however,

suffer from a number of limitations:

1) Interpretations are ambiguous. Consequently, independent geophysical andgeological controls are necessary to discriminate between valid alternative

interpretations of the resistivity data.

2) Interpretation is limited to simple structural configurations. Any deviations fromthese simple situations may be impossible to interpret.

3) Topography and the effects of near-surface resistivity variations can mask theeffects of deeper variations.

4) The depth of penetration of the method is limited by the electrical power and themaximum AB separation.

5) The trend of the electrode configuration can effect on the interpretation.

4.6Data Interpretation:

4.6.1Qualitative Interpretation:

4.6.1.1Resistivity Curve Type:

In the field measurement, the results of VES are presented in form of curves

having apparent resistivity plotted as function of AB/2 on bi-logarithmic graphs. These

give the general variation of apparent resistivity with depth depending on the variation of


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4.6.1.2Pseudo-section:

It is a graphical representation of apparent resistivity, where the VES separation

along the profile is placed on x-axis "linear scale" and AB/2 is placed on y-axis "log

measured at each VES at various AB/2. This section describes the variation of apparent

resistivity laterally (between VESs) and vertically (the depth).See the location of each

profile in figure 4.7.

o Along profile A-A: This section is extended for 33.8 km. The variation ishomogeneous in the right-hand side while there is a high apparent resistivity zone

in the left-hand side which has a circle shape with variation in range 400 to 850

.m (figure 4.8).

o Along profil e B-B: This section is extended for 17.7 km. There are two highapparent resistivity zones. First zone is the upper right corner while the variation

is in range 100 to 250 .m. The second zone is in the lower left corner which has

variation in range 100 to 450 .m (figure 4.9).

o Along profil e C-C: This section is extended for 10.4 km. The variation inapparent resistivity is homogeneous except in three high zones. First zone is upper

of the map directly beneath VES 4, the variation is in range 60 to 180 .m.

Second zone is in the lower right corner which the variation is in range 60 to 150

.m. Third zone is in the lower left corner which the variation is in range 60 to

240 .m (figure 4.10).

oAlong profil e D-

D: This section is extended for 16.1 km. The apparent resistivity

is generally decreased toward the right-hand side, but there are three zones

noticed in the map. First zone is a high zone located in the upper left corner which

scale", then the intersection points are contoured according to the apparent resistivity


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Figure 4.10: shows the Pseudo-section along profile C-C.


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4.6.2Quantitative Interpretation:

4.6.2.1

True Resistivity determination:

During the survey we measure the

apparent resistivity variation in the sub surface

Figure 4.12: shows the Pseudo-section along profile E-E.


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o Profi le C-C:This profile is extended for 18.7 km, from VB 20 in the west of themap to borehole BH 20 "the lithology is unknown" passing through VB 19. VB

18, VB 17, VES 9, VES 4, and silicified sandstone outcrop (figure 4.16).Structurally, there is only one normal fault revealed in this section and confirmed

by the gravity curve (figure 4.16 A), the down thrown is in the right-hand side (to

the east of the map), this fault maybe has trend of N-S or close to it, the location

of the fault does not agree with the gravity data, maybe because the gravity

exploration was regionally. Lithologically, on the left-hand side (up-thrown zone)

there is a thin layer of sands overlies the claystone which has varied in thickness

in range 20 to 40 m, this layer overlies the Basement Complex which is varied indepth in range 30 to 60 m. On the right-hand side (down thrown zone) there is a

layer of sands and sandstone extended from the fault plane with maximum in

thickness and decreased toward the silicified sandstone then appear again with

thin layer at BH 20. The lithology of BH 20 is estimated from profile A-A' which

is close to it. The pinch-out of silicified sandstone is disappearing before reach

VES 4, the maximum thickness detected for it is 20 m. This layer overlies a thick

layer of claystone has maximum thickness at the fault plane "about 50 m" and

decreased toward BH 20 until has thickness 20 m. The Basement is underlie the

claystone in the left side of the down thrown zone, and in the rest of it is covered

by pinch-out clayey sandstone known from profile A-A'. The depth of Basement

in the down thrown zone is about 70 to 110 m (figure 4.16 B).

o Profile D-D:This profile extended for 16.1 km from the VES 11 in the west ofthe map to VES 2 in the middle of the map passing through a Basement Complex

outcrop, VB 14, and VB 13 (figure 4.17). Structurally, the basement outcrop is

flanked by normal fault in both sides, on the left-hand side the fault is gentle with

t d f NW SE thi t d i t d b f d th d th f B C t b h l 14 t


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sandstone varied in thickness in range 20 - 60 m. This layer overlies the

Basement Complex. The depth of the Basement at the first up-thrown is started by

120 m at the fault plane beneath VES 8 and increased in depth toward the west(toward VES 7), at the down thrown the depth of the Basement is about 230 m,

and at the second up-thrown is about 55 m (figure 4.18 B).


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5.2Results of The Gravity and Sounding Resistivity Methods:

On the basis of the gravity results, the high residual gravity values are attributed

to the occurrence of shallow Basement Complex, while the low residual gravity values

are attributed to the accumulation of relatively thicker sediments filling the depression of

the Basement Complex (figure 5.2).

According to these assumptions, there are three low residual gravity zones as

shown in the figure 5.2, these zones are located in the northern and the southern parts of

the map. These zones reveal the present of the basins. All the depressions revealed in the

study area are bounded by relatively steep gradients which are considered to be fault

lines. The dominant trends of these faults are NW-SE and NNE-SSW directions. The

remaining parts of the area are underlain by relatively shallow Basement Complex.

On the other hand, the sounding resistivity measurements are limited in the

western part of the White Nile river in the study area (figure 5.1), most of the sounding

measurements have shown infinite trends (for basement Complex) at relatively small

current separation (AB/2) in the range 150 to 700 m (table 4.1). The presence of goodborehole information and general proximity Basement outcrops to the sounding stations

have provided a strong control for the sounding inversion. The sounding resistivity

interpretation shows a rapid facies change in the sediments over the study area.

The results of the sounding interpretation confirm that there is increasing in depth

of the basement Complex from the south toward the north and northwest of the study area

in the west of the White Nile river with respect to present of some Basement outcropsthere (Jebel Helbi).


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Three major basins are obvious on the structural contour map (figure 5.3) and

confirmed by the residual gravity anomalies (figure 5.3):

o Umm Andraba basin :is located in the north western part of the map (figure 5.3),the basin was generated by the block subsidence during several stages of rifting.

This basin has maximum depth about 950 m, its dimension is about 18 km in NE-

SW trend and about 20 km in SW-NE trend. Two profiles are passing through this

basin (figure 5.3), profile X-X' (figure 5.4), and profile Y-Y' (figure 5.5).

o Shikh Sidig basin :is located in the southeast direction to the Um Andraba basin,and separated from it by shallow Basement Complex. Also between them there is

a Basement Complex outcrop (figure 5.3). The basin was generated by the block

subsidence during several stages of rifting. This basin has maximum depth about

1100 m, its dimension is about 14 km in NW-SE trend, and about 10 km in NE-

SW trend. Two profiles are passing through this basin (figure 5.3), profile X-X'

(figure 5.4), and profile Z-Z' (figure 5.6).

o Abu Agaga basin:is located in the southern part of the map in the east side of theWhite Nile river (figure 5.3). Only the northern part of this basin is appear on thestructural contour map and its north western side of this basin extend to the west

of the White Nile river. This extension was interpreted by Hassan, B, (2009) as

the Alaga basin, the problem was in the study of the west of the river only without

review the previous studies in the surrounding area. The maximum depth can be

noted on the map for this basin is about 1350 m. From the Bouguer anomaly map

(figure 3.2 in chapter 3), the dimension can be detected, which is about 12 km in

N-S trend and about 30 km in E-W trend. Profile Z-Z' is passing through thisbasin (figure 5.6).


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X-X

',(A)

ResidualGravityanoma

ly.

(B)Geologicalsectio

n.


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Y-Y',(A)ResidualGravityanomaly.

(B)Geologicalsection.


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References

Brooks, M. & Keary, P. (1984), An Introduction to Geophysical Exploration.

Blackwell Scientific Publications, Oxford (1st edn)

Dobrin, M.B. (1976), Introduction to Geophysical Prospecting. McGraw-Hill,

New York (3rd edn).

El Dawi, M.G, (1997), Gravity and Vertical Electrical Sounding Investigation in

the area of Khartoum State eats of the River Nile.

Farwa, A.G. (1978), Geology and Structure of the Gezira Area as Deduced from

Gravity Measurements.

Hassan, B.A (2009), Application of the Gravity and Resistivity Methods to

Delineate The Subsurface Structures of The Area West of The White Nile, Sudan.

Hersi, A (2004), Geophysical Investigation for Groundwater Southern Gezira,Sudan.

Kheiralla, M.K. (1966), A study of The Nubian Sandstone Formation of the Nile

Valley between 14N and 17.42N with reference to the Groundwater Geology.

Mabrook, B.M (1972),Geologic and Hydrogeological Studies of the East

Kordofan Area, Sudan

Milsom, J (2003), Field Geophysics.


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No. Longitude

(degree)

Latitude

(degree)

Elevation

(m)

Bouguer

Anomaly

(mGal)

73 32.35 14.45 385.7 -41.5

74 32.37 14.45 385.7 -42.1

75 32.4 14.45 386.34 -39

76 32.42 14.45 386.7 -38.4

77 31.6 14.5 388.5 -26.4

78 31.62 14.5 389.6 -30

79 31.65 14.5 387.89 -31.4

80 31.67 14.5 387.71 -35.9

81 31.84 14.5 385.8 -30

82 31.89 14.5 384.34 -27.9

83 31.91 14.5 384.19 -28.5

84 31.92 14.5 384.07 -24.5

85 31.94 14.5 383.85 -31

86 32.07 14.5 382.6 -26.8

87 32.07 14.5 381.82 -21.5

88 32.27 14.5 381.2 -50.4

89 32.28 14.5 382.2 -54.5

90 32.31 14.5 383.38 -54

91 32.34 14.5 384.2 -57.5

92 32.36 14.5 384.2 -58

93 32.38 14.5 385.35 -57.4

94 32.4 14.57 385.95 -39.7

95 32.47 14.57 388.4 -37.296 31.55 14.6 388.06 -29.8

97 31 57 14 6 388 79 28 4


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No. Longitude

(degree)

Latitude

(degree)

Elevation

(m)

Bouguer

Anomaly

(mGal)

197 32.5 14.9 386.2 -24.3

198 31.64 15 380.59 -31.6

199 31.69 15 385.9 -30.3

200 31.7 15 381.6 -32.7

201 31.71 15 381.24 -31.5

202 31.72 15 386.02 -31.4

203 31.73 15 381.69 -33.4

204 31.75 15 386.37 -31.7

205 31.76 15 386.45 -28.8

206 31.79 15 385.99 -24.4

207 31.83 15 385.9 -26

208 31.88 15 387.2 -26.8

209 31.93 15 386.09 -26.3

210 32 15 385.9 -28.8

211 32.04 15 385.13 -31.7

212 32.05 15 385.25 -32.3213 32.08 15 384.57 -33.8

214 32.09 15 384.2 -31.8

215 32.13 15 385.68 -37

216 32.28 15 382.52 -26.1

217 32.29 15 382.52 -31.8

218 32.34 15 381.03 -23.8

219 32.35 15 380.94 -19.3220 32.5 15.05 384.7 -24.1

221 32 53 15 05 384 7 27 2


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No. Longitude

(degree)

Latitude

(degree)

Elevation

(m)

Bouguer

Anomaly

(mGal)

238 32.07 15.17 384.2 -31.2

239 32.1 15.17 384.39 -33.5

240 32.16 15.17 384.85 -30.1

241 32.22 15.17 384.01 -24.5

242 32.26 15.18 383.28 -24.3

243 32.28 15.18 383.46 -23.3

244 31.87 15.2 381.14 -32.8

245 31.88 15.2 380.69 -29.3

246 32.11 15.2 384.48 -30.4

247 32.32 15.2 383.17 -21.8

248 32.35 15.2 382.71 -18.2

249 32.4 15.2 381.21 -21.7

250 32.42 15.2 381.12 -19.2

251 32.5 15.2 380.79 -22.2

252 32.25 15.22 383.28 -22.5

253 32.41 15.22 381.23 -20.2254 32.5 15.23 380.95 -18.8

255 32.52 15.25 379.48 -29

256 32.14 15.27 384.94 -37.6

257 32.26 15.27 382.63 -21.6

258 32.26 15.28 382.63 -20.9

259 32.47 15.28 380.41 -21.5

260 31.85 15.3 381.42 -38.4261 31.87 15.3 381.78 -35.7

262 31 92 15 3 381 96 33 8


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Longitude

(degree)

Latitude

(degree)

Bouguer

mGal

Regional

mGal

Residual

mGal

31.6167 14.4167 -24.3 -21.7 -2.6 BH 1 EL HUNO

31.6500 14.4500 -28.8 -25.4 -3.4 BH 2 MUGRIANT

32.16 14.757 -19.8 -18.0 -1.8 BH 3 AL ALAGA

31.7667 14.1167 -23.7 -21.7 -2.0 BH 4 EL BIHAER

31.7833 14.7000 -24.7 -21.5 -3.2 BH 5 HAGIBA

31.8333 14.4667 -28.1 -26.1 -2.0 BH 6 EL HUMRAYA EL MAGDIA

31.8833 15.2000 -30.1 -27.9 -2.2 BH 7 UM ANDRABA

31.9000 15.0333 -27.1 -24.5 -2.5 BH 8 EL SHIGIG

32.0000 14.5000 -27.7 -25.1 -2.7 BH 9 ESSYAL

32.0056 14.0006 -29.8 -28.3 -1.5 BH 10 EL DUEIM 132.0125 14.8333 -20.7 -19.2 -1.5 BH 11 EL GETAINA

32.0167 14.2833 -27.6 -25.8 -1.8 BH 12 AWLAD EL EBIAD 4719

32.0333 14.3333 -28.4 -26.4 -2.0 BH 13 EL SILEIK

32.0333 14.7917 -20.6 -20.2 -0.4 BH 14 UMM ESHUSHAT

32.0333 15.2667 -33.9 -33.4 -0.5 BH 15 EL HUWIDA

32.1333 14.4000 -31.3 -27.5 -3.8 BH 16 GOZ EL BIED

32.1333 14.9167 -26.3 -24.2 -2.0 BH 17 UMM NALA (B)

32.1833 14.3833 -33.6 -31.9 -1.8 BH 18 EL SHETEIB

32.2000 14.7333 -20.7 -19.3 -1.4 BH 19 EL SHAWAF

32.2000 14.8167 -21.2 -19.9 -1.3 BH 20 HAFEIR ELFAKI ABEDELB

32.2167 14.2333 -38.3 -37.1 -1.3 BH 21 WAD EL ABYAD

32.2167 14.0167 -22.6 -20.7 -1.9 BH 22 EL MENSURA 2398

32.2833 14.63 -25.9 -21.3 -4.6 BH 23 ABU AGAG

32.3167 14.8833 -22.2 -21.1 -1.1 BH 24 EL SCHITAB

32.3167 14.9167 -25.0 -24.6 -0.5 BH 25 EL TILUH32.4333 14.8000 -14.3 -13.1 -1.2 BH 26 WAD EL HEDEBA

32 4333 15 2000 -19 2 -17 9 -1 3 BH 27 EL MANDRA


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Longitude

(degree)

Latitude

(degree)

Bouguer

mGal

Regional

mGal

Residual

mGal

32.0878204 15.21387 -32.0 -30.3 -1.7

32.0386318 15.16468 -30.9 -29.7 -1.3

32.1042167 15.16468 -33.0 -29.8 -3.232.1838555 15.16702 -28.5 -27.7 -0.8

32.2377288 15.16234 -26.4 -26.3 -0.1

32.2962868 15.16234 -23.5 -24.5 1.0

32.3595293 15.16234 -20.8 -22.1 1.4

32.4297989 15.15765 -20.3 -20.1 -0.2

32.4930415 15.15297 -22.7 -20.3 -2.4

32.5539417 15.15297 -27.9 -22.0

-5.932.5726803 15.09909 -29.0 -23.9 -5.1

32.5094377 15.09675 -24.5 -23.0 -1.5

32.4461951 15.08972 -21.5 -22.8 1.3

32.3876372 15.09207 -20.9 -23.5 2.6

32.3267369 15.09909 -25.5 -25.0 -0.4

32.2470981 15.09909 -29.8 -27.1 -2.8

32.2049364 15.09909 -30.6 -27.6 -3.0

32.1252975 15.09207 -33.3 -28.0 -5.3

32.0386318 15.08972 -31.7 -27.7 -4.0

32.0433164 15.02648 -32.4 -26.1 -6.3

32.1252975 15.02414 -35.2 -13.2 -22.0

32.2236749 15.02648 -28.7 -28.4 -0.3

32.305656 15.02414 -27.7 -26.3 -1.3

32.3806102 15.02414 -20.9 -24.7 3.8

32.4696183 15.02414 -24.0 -24.7 0.732.563311 14.96792 -28.8 -27.8 -1.0

32.4836722 14.96558 -27.2 -26.2 -1.0


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VES Name

Longitude

(degree)

Latitude

(degree) VES Name

Longitude

(degree)

Latitude

(degree)

VES 1 32.16 14.757 VB 8 32.25 14.88

VES 2 32.159 14.786 VB 9 32.16 14.88

VES 3 32.064 14.765 VB 10 32.25 14.85

VES 4 32.134 14.84 VB 11 32.19 14.81

VES 6 32.156 14.749 VB 12 32.12 14.73

VES 7 32.15 14.95 VB 13 32.12 14.77

VES 8 32.2 14.96 VB 14 32.09 14.77

VES 9 32.103 14.846 VB 17 32.08 14.85

VES 10 32.17 14.92 VB 18 32.07 14.85

VES 11 32.026 14.763 VB 19 32.05 14.85

VES 12 32.125 14.824 VB 20 32.04 14.85

VES 13 32.11 14.69 VB 21 32.07 14.88

VES 14 32.11 14.68 VB 22 32.04 14.9

VES 15 32.073 14.791 VB 23 32.03 14.88

VES 16 32.167 14.757 VB 24 32.06 14.91

The Coordinates of Each VES

Appendix- B

Resistivity Data

AB/2 MN/2 VES 1 VES 2 VES 3 VES 4 VES 5 VES 6 VES 7 VES 8 VES 9 VES 10 VES 11


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AB/2 MN/2 VES 1 VES 2 VES 3 VES 4 VES 5 VES 6 VES 7 VES 8 VES 9 VES 10 VES 11

1.5 0.5 35 7 57 45 44.913 10 185 45 187 263 153

2.5 0.5 31 8 59 42 42.182 9 103 33 153 190 132

4 0.5 25 9 58 37 39.56 8 81 40 118 126 120

6 0.5 19 12 57 34 31.781 8 85 52 88 92 100

8 0.5 16 15 55 34 34.6 8 95 61 72 75 8110 0.5 14 18 52 40 37.56 7 108 71 66 63 77

12 0.5 13 21 49 44 431.607 7 123 80 62 54 66

15 0.5 12 23 43 56 477.256 7 145 88 61 44 57

20 5 11 19 40 65 66.721 8 165 98 57 33 40

25 5 12 22 32 71 65.375 9 194 108 57 33 32

30 5 13 21 26 75 71.448 10 216 128 53 26 24

40 10 14 19 22 97 78.892 10 272 153 43.3 22 17

50 10 15 18 19 104 102.482 11 310 178 37 17 14

60 10 16 13 19 109 113.197 12 339 196 30.7 14 1375 10 17 19 19 147 108.674 12 377 220 24.5 13 13

100 25 22 9 20 156 177.229 14 449 342 19.17 12.5 13.5

125 25 24 9 19 150 169.56 13 470 392 17.8 13.5 15

150 25 27 8 21 147 151.118 12 516 450 18.1 17 17

175 50 29 9 21 129 160.724 14 510 453 27.8 20 19

200 50 31 10 21 117 135.413 12.7 498 480 30 22.5 21

250 50 34 21 111 160.14 10.9 461 508 37 27 25.8

300 50 35 22 107 107.172 9.7 400 525 44.3 33 33

400 100 39 26 143 122.46 9.4 313 453 70.5 37 36

500 100 23 158 188.4 8.9 233 497 84.9 46 45

600 100 188 9.4 182 544

700 100 150.7 188.4 142 621

800 100

900 100

1000 100

AB/2 MN/2 VES 12 VES 13 VES 14 VES 15 VES 16 VB 1 VB 2 VB 3 VB 4 VB 5 VB 6


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AB/2 MN/2 VES 12 VES 13 VES 14 VES 15 VES 16 VB 1 VB 2 VB 3 VB 4 VB 5 VB 6

1.5 0.5 18.7 50 31 31.31 20 47 123.8 144 21 128 107

2.5 0.5 24.2 33 36 36.36 13 39 101 120 38 170 207

4 0.5 30 28 39 39.6 9 32 1.5 120 50 133 68

6 0.5 32 25 38 38 8 26 124 168 100 184 66

8 0.5 31 23 35 35 8 20 129 220 153 177 9510 0.5 27 20 31 31.3 9 13 140 265 174 189 100

12 0.5 23 20 26 26 9 13 144 114 125 209 168

15 0.5 17 18 21 17 8 9 157 113 228 235 181

20 5 12 14 14 13 9 6.6 184 70 10 279 57

25 5 9 13 13 13.3 9 7 221 68 9 326 80

30 5 7 13 13 12 10 6 254 72 9 385 72

40 10 6.7 13 12 12.5 11 9 317 73 11 485 90

50 10 6.7 13 13 12.8 12 7.8 393 76 12 616 112

60 10 6.6 13 14 12.08 14.5 10 470 79 16 707 105

75 10 7 13 15 15.6 16 12 552 86 16 749 109

100 25 8 13 17 17.8 15 12.5 714 84 15 893 106

125 25 8.8 12 18 19.8 15 14.7 789 78 22 1000 107

150 25 12 19 20 15 15 882 77 22 712 111

175 50 9.2 15 21 21 13 16 701 78 22 792 111

200 50 10 15 22 22.37 12 19 769 77 21 869 108

250 50 10.6 18 244 22.61 10 19 840 70 21 939 100

300 50 12 22 22 22.7 7 19 728 63 24 877 99

400 100 26 28 23.55 4 20 742 55 25 881 84

500 100 31 33 25.4 31 637 39 35 801 85

600 100 37 27.48 33.7 629 41 40 775 90

700 100 30.14 30.5 551 45 45 596 91

800 100 20 400 49 61 500 80

900 100 25.8 279 728 60 482 76

1000 100 31.4 219 683 51 438 62


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AB/2 MN/2 VB 20 VB 21 VB22 VB 23 VB 24 VB 25 vb 26 VB 28 VB 29 VB 30 VB 31


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/ /

1.5 0.5 39 336 139 129 37 48 121 94 57 185 42

2.5 0.5 38 35 137 129 39 48 114 75 58 209 46

4 0.5 38 35 146 133 36 48 90 74 58 225 42

6 0.5 37 37 144 129 42 48 86 78 61 227 33

8 0.5 37 34 144 131 48 44 76 85 64 222 2610 0.5 36 34 141 129 58 43 75 89 71 216 36

12 0.5 35 32 131 133 65 42 66 129 73 210 33

15 0.5 49 20 150 136 85 39 94 150 83 204 30

20 5 50 18 180 176 63 37 99 122 99 188 30

25 5 51 16 151 171 93 61 107 150 110 181 15

30 5 60 12 132 178 112 52 124 184 122 181 13

40 10 59 10 102 176 125 46 148 142 131 181 11

50 10 63 10 91 205 87 41 180 198 135 203 11

60 10 72 10 97 242 101 53 214 235 148 209 10

75 10 86 10 130 261 122 48 251 288 167 222 11

100 25 104 12 196 303 135 42 365 385 185 238 12

125 25 83 14 226 339 167 41 405 319 213 255 16

150 25 107 260 276 183 38 501 396 173 284 21

175 50 149 293 250 245 26 216 383 33

200 50 141 346 199 277 31 428 39

250 50 157 218 154 36 446

300 50 181 244 189 36 489

400 100 209 258

500 100 237 368

600 100 215 400

700 100 254 427

800 100

900 100

1000 100

Integration of the Gravity and Sounding Resistivity Methods to Study the Subsurface Geology and Structures in the Area North of the White Nile State, Sudan

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