SD9700016

X-RA Y DIFFRACTION ANALYSES OF CLAY STONES,MUGLAD SEDIMENTARY BASIN .

SUDAN

A THESIS SUBMITTED IN PARTIALFULFILLMENT FOR THE DEGREE

OF MASTER OF SCIENCE INPHYSICS

BYAMMAR ELSIDDIG ALI

DEPARTMENT OF PHYSICSFACULTY OF SCIENCE

UNIVERSITY OF KHARTOUM

JANUARY 1997

-06

We regret thatsome of the pagesin this report may

not be up to theproper legibilitystandards, eventhough the best

possible copy wasused for scanning

ACKNOWLEDGMENT

VIwish to express may gratitude and indebtedness to my former supervisor

Dr. Osman Dawi Eisa for the insight he gave to me into my research and

laboratory work.

My gratitude is also due to Dr. Osman M. Abdullatif who carefully

supervised this work in the stage of writing; Mr. Hassan H. Elhussein for helping

me to master the XRD system and accessories; Dr. M. H. Shaddad for his help in

maintaining the lab printer and in changing the analyses program; Mr. Ali

Elssaied for his help in sample preparation; Mrs. Sadia Elsier for helping me

typing the thesis in the computer; Finally and before all my gratitude is due to my

family for the healthy atmosphere ana encouragement that they gifted to me.

ABSTRACT

This study deals with the theoretical and experimental aspects of X-

ray diffraction (XRD) technique. Moreover, the XRD technique has been

used to investigate the clay mineral types and their distribution for samples

obtained from exploration wells in the Muglad sedimentary basin in

western Sudan. The studied samples range in depth from 1524m to

4572m.

The XRD analysis of samples shows that they consist of kaolinite,

smectite, illite, chlorite and the mixed - layer smectite / illite. Kaolinite has

higher abundance (15 - 72%) followed by illite (7 - 34%), smectite (11-

76%) and the less abundance of chlorite and the mixed - layer smectite /

illife. Non-clay minerals found include quartz and cristabolite.

The clay mineral types and their vertical distribution reflect various

controls such as environmental, burial diagenesis, source rocks and

climatic influences in the Muglad sedimentary basin.

4\\\ ...H V A>

.Ufti

j j j jSJLS Lxiikll j j t

JJJJ J j

J dulV Ao

List of tables & Figs.

Page no.

Fig. II-1 Aunit cell 4

Fig. II-2 Aplane specified by the Miller indices 6

Fig. II-3 Diffraction of x-rays by a crystal 8

Fig. II-4 Coherent scattering of x-rays by asingle electron 11

Fig. III-l X-ray tube 15

Fig. III-2 The generation of x-rays of a line spectrum of copper due to the

transfer of electrons into the K shell 18

Fig III-3 Geoniometer 20

Fig. III-4 DACO-MP program 23

Fig. IV-1 Structure of clay minerals 30

Fig IV-2 Change of clay minerals with increasing depth of burial 31

Fig. IV-3 Vertical distribution of clay minerals 32

Table IV-1 Summary of behaviours of the clay minerals towards

identification treatments 33

Table IV-2 Clay mineral types percentages in sample measured 34

XRD charts 35

CONTENTS

Page no.

Acknovvlegment i

Abstract ii

List of tables and figures iv

CHAPTER-I Introduction

Objective and scope 1

Methods 2

CHAPTER -II Theoretical background

II-O Crystal and crystal lattice 3

II-1 Crystal system 3

II-3 Miller indicies 3

II-4 X-ray diffraction 7

II-4-1 Introduction 7

II-4-2 Bragg low 7

II-4-3 DifFractiondirection 9

II-4-4 Scattering of x-rays by an electron 10

II-4-5 scattering of x-rays by atom 12

II-4-6 Scattering by a unit cell :.;13

II-4-7 Temperature factor 13

CHAPTER -III Experimental techniqes and data processing

Page no.

III-1 Introduction 14

III-2 Production of x-rays 14

III-3 The x-ray generator 16

111-4 The x-ray tube 17

III-5 The cooling system .':• 17

III-6 Monochromotization '. 17

III-7 The goniometer , 19

III-8 The detector 19

III-9 The DACO-MP 21

111-10 Sample preparation and separtion ,22

III-l 1 Data collection...., .7. 22

111-12 Data processing :..". 24

CHAPTER-IV Results,interpretations and conclusions

IV-1 Introduction 26

IV-2 Nature and crystal structure of clays 26

IV-3 Methods of interpretation 27

IV-4 XRD results 27

IV-5 Interpretation, discussion and conclusion 28

References 52

CHAPTER(I)

INTRODUCTION

After the discovery of X- rays in 1895 it was realized that many of their

properties could be explained if they were subjected to electromagnetic

radiation with a wave-length much shorter than for ordinary light.

Van lane in 1912 discovered that crystals act as a diffraction gratings for

X-rays. Many experiments followed. For example, the experiment done by

Frederick and Knipping [Thewlis et al., 1962] lead to the use of X-ray

diffraction as a mean of studying the regular arrangement of atom and

molecules in crystals.

Since then X-ray diffraction (XRD) technique has proved to be a good

tool for investigating the fine structure of matter. At first (XRD) was used only

for the determination of crystal structure. Later on, other uses where developed,

and today the method is applied not only to structure determination, but to

such diverse problems as chemical analysis, stress measurement, the study of

phase equilibria, the measurement of particle size, the determination of the

orientation of crystal or the ensemble of orientation on polycrystalline

aggregate [Cullity 1978]

Methods or techniques of (XRD) were improved with time. Now it has the

advantage, with modern instrumentation, and complete automation, fast and

precise results are obtained. The theoretical and practical aspects of XRD, the

application and interpretation aspects and clay mineral identification and

quantification, all have been comprehensively treated in the literature

(Zussman, 1977; Tucker, 1988; Carol, 1970;Thorez, 1975).

In the mineralogical analysis of rocks (XRD) is a basic tool, and in the

case of fine grained sediments (clays) it is an essential one [Tucker 1991]. Clay

minerals are the most abundant minerals at the surface of the earth . This is

illustrated by the fact that they are, with quartz, the main constituents of

mudrocks which constitute between 45% to 75% of the total volume of

sediments [Tucker, 1991]. mud rocks can be deposited in different environments

such as river floodplains, lakes, deltas and deep sea. The data collected from

clay minerals is useful in understanding the geological processes

,environmental and climatic conditions as well as the control of successive

internal and surficial geodynamical factors (Tucker, 1991,Chamley,1989).

Objective and Scope :-

In this project the technique of (XRD) is used to investigate the clay

minerals of some collected subsurface clayston samples from Abu Gabra and

Sharaf formations in the Muglad sedimentary Basin in western Sudan. The

results of the samples analyses were analyzed to see the effect of vanes_ V

controlling factors on clay mineral types and their distribution .

Methods :

The samples investigated range in depth from 1524 to 4572m. These

samples represent sediments deposited mainly within lacustrine environments.

After sample preparation and separation, oriented mounts of the < 2 micron j>i

clay fraction were prepared.Then XRD analyses were measured by Siemens

diffractometer with its DACO-MP which uses a program called Analyses.

These analyses were carried out under normal (dry), ethylene glycol and

heating treatments. Then the clay minerals were identified and determined

qualitatively and semi-quantitatively according to change of basal spacing

under the three treatments and reJt.tive peak hights.

The thesis is written in four chapters, chapter (I) is the introduction,

chaptcr(II) is the theoretical background, chapter(III) is the experimental

technique and finally the results, discussion and conclusion are presented in

chapter (IV).

Chapter (II)

THEORETICAL BACKGROUND

(II-O) INTRODUCTION :

This chapter deals with some concepts of solid state physics and the

intensity of diffraction and the factors which affecting this intensity.

(III) CRYSTAL AND CRYSTAL LATTICE :

A crystal is defined as "a solid composed of atoms arranged in a pattern

periodic in three dimensions'Mf one considers any point within the crystal,

then there are other points within the crystal that are in the same

conditions.The arrangement of these points constitute a crystal lattice.

The crystal is usually defined by three translation vectors a,b and c along

the three axis incline^to each other at angles a , P , y. The smallest unit of \

volume of the lattice with side equal to a, b and c is called a unit cell which

when repeated gives the crystal lattice [fig(II.l)].

(II-2) CRYSTAL SYSTEM:

When there are lattice points only at each corner of the unit cell, the unit

cell contains one basic unit of structure, which if repeated will build up the

crystal. Such a unit cell is called a primitive cell with symbol P.

Some unit cells contain more than one unit of structure and they are

referred to as non primitive (Cullity, 1978).

There are fourteen primitive and non primitive lattices, they are called

Bravias lattices. [Cullity 1978].

*»* b

F»g. H-l A unit cell

(II-3) MILLER INDICES :

The Miller indicics are defined as the reciprocals of fractional intercepts

which the plane makes with the crystallographic axis .If the Miller indices of

plane are (hkl) then [(hkl)]arQ the indices of the direction of the line passing

through the plane. The plane makes fraction intercepts 1/fi, 1/k ,1/1, with the

axis, and , if the axial lengths are a, b, c, the plane makes actual intercepts of

a/h , b/k , c/l, [fig(II.2)j. Parallel to any plane in any lattice, there is a whole

set of parallel equidistant planes, one of which passes through the origin. If a

plane is parallel to a given axis, its fractional intercept on that axis is infinity

and corresponding Miller index is zero .If the plane cuts a negative axis, the

corresponding index is negative and is written with a bar over it. Planes whose

indices are the negative of one another are parallel and lie on opposite sides of

the origin , e.g. ( 2 1 0 ) and (27 0).

The interplanear spacing dm > measured at right angles to the planes, is a

function of both the plane indices (hkl) and the lattice constants (a,b,c,a,P, y).

The exact relation depends on the crystal system involved and for the cubic

system forixample [Cullity, 1978]

dvM (cubic) =

for tetragonal

at {tetragonal) = -

>•*•!. '

Fig. 11-2 A plane specified by the Miller indices (hkl)

(II-4) X-RAY DIFFRACTION :

(II-4-1) INTRODUCTION :

A crystal is composed of regularly spaced atoms which act as scattering

centres of X-rays and since X-rays are of wave-length equal to.or close to the

interatomic distance in crystal , then diffraction of X-rays takes place by

crystal. This was in fact demonstrated by Van laue in 1912.

The diffracted beam may be defined as a beam composed of a large

number of scattered rays mutually reinforcing one another. The atoms of a

crystal scatter incident X-rays in all direction, but. some of these scattered

beams will be completely in phase and so reinforce each other to form

diffracted beams.

(II-4-2) BRAGG LAW:

Consider rays 1 and la [fig (113)] striking the atoms K and P in the first

plane of the atom and scattered in direction 1 and la . The difference in their

path length between the wave front XX and YY is equal to

QK-PR = PKcos8 - PK cos6 = 0

Also rays 1 and 2 scattered by atoms K & Land the path difference for

the rays lKl'and2L2 is

ML + LN -d sinO + d sine

If the scattered rays 1 and 2 are in phase and there' path difference is

equal to a whole number n of wave-length \, then

nX = 2d sin0

c -

Fig 11-3 Diffraction of X-ray by a crystal

Where

X = wave-length.

d ~ spacing between planes .

9 = the angle between the incident beam and reflecting beam

This above relation is known as Bragg law, n is called the order of

reflection it takes integral values .For fixed values of X and d , there may be

several angles of incidence 9i, 62; O3, at which diffraction may occur,

corresponding to n = 1, 2, 3,

The form of Bragg law normally used is

K = 2dsin8

where d = ( d /n )

(II-4-3) DIFFRACTION DIRECTIONS :

Various diffraction angles can be obtained from the (100) planes and

produce first, second, third, order reflections.Also diffraction can be

produced by the (110) planes, the (111) planes, the (213) planes and so on. A

general relation which will predict the diffraction angle for any set of planes

can be obtained by combining Bragg equation (X = 2^sin6), and the

interplaner spacing d(wu> > for the cubic system.

Thus

4a1

This equation predicts, for cubic cell, all the possible Bragg angles at

which diffraction can occur from the planes (Jikl).

1 .

(II-4-4) Scattering of X-rays by an electron :

The intensity of the scattered beam depend on the angle of scattering. The

intensity / of the beam scattered by single electron of charge e coulombs and

mass m Kg , at distance r meter from the electron, is given by

"Un

Where /„ is the intensity of the incident beam, jio= 47rxlO"7mKc"2, K =

constant and a is the angle between the scattering direction and the direction of

the acceleration of the electron (Cullity 1978).If the incident beam is traveling in

the direction OX encounters an electron at O (fig II.4),then this will have an

electric vector E,which may be resolved into plane-polarized components Eyand

The Ey of the incident beam accelerates the electron in the direction OY. It

therefore gives rise to a scattered beam whose intensity at P is found to be

Since a = 7i/2, the intensity of the Z-component is given by

\

I% io

Fig 11-4 Coherent scattering of x-rays by a single electron

I I

The total intensity nt P is givsn by

_/,,A"f 1 +cos2 26

The quantity -( l + cos2 20) is known as the polarization factor.

(11-4 -5) SCATTERING BY AN ATOM :

The efficiency of scattering X-rays by a given atom in a given direction is

described by a quantity/called the atomic scattering factor, which is a ratio of

amplitudes

s=A-

Where Aa is the amplitude of the wave scattered by an atom and Ae is the

amplitude of the wave scattered by one electron. Since the intensity of the

scattered wave is proportional to the square of the amplitude then we have

Where /() and Ie is the intensity of the rays scattered by the atom and

electron respectively.

12

(11-4-6) SCATTERING BY A UNIT CELL :

Since the scattering from an atom depend'on the distribution of its electrons

and the scattering from a unit cell depend on the atomic arrangements, the most

important factor in the study of scattering by a unit cell is the structure factor

.This is defined as the ratio of the amplitude of the wave scattered by all atoms

in the cell to the amplitude of the wave scattered by one electron and is denoted

by i F {hkl) I

\F(hkf)\ =[(FcQsa)2+(Fs\na)2}>

Where a is the angle of the composite wave due to all kinds of atoms.

(II-4-7)TEMPERATURE FACTOR

Since / is the atomic scattering factor of an atom undergoing thermal

vibration, / , is the factor for an atom at rest then

/ = /(,exp[-B(sin0)2/^2]

Where B is called the temperature factor and depends on the type of the

atom and the orientation of the reflecting planes in the crystal ,6 is the Bragg

angle and X is the wavelength [Cullity 1978].

13

Chapter (III)

EXPERIMENTAL TECHNIQUE

AND DATA PROCESSING

(III-l) INTRODUCTION :

This chapter describes how a Siemens diflxactometer, a DACO-MP and

an X-ray generator with its cooling system can be used to measure the

dilli actograms of the samples. The procedures of samples preparation and

separation shall also be presented.

(111-2) PRODUCTION OF X-RAYS :

X-rays are produced whenever high-speed electrons collide with a metal

target. The main constituents of the X-ray tube are source of electrons

(filament), a high accelerating voltage and a metal target. Because most of the

kinetic energy of the electrons is converted into heat in the target, the later is

almost always water cooled to prevent its melting. The tube used is a filament

tube consisting of an evacuated glass envelope which insulates the anode at one

end and the cathode at the other end ,[fig (IH-l)], the cathode being a tungsten

filament and the anode a cooled block of a desired target metal as small insert

at one end. One lead of the high voltage transformer is connected to the

filament and the other to the ground, the target being grounded by its own

cooling water connection. The filament is heated by a current of about 3 Amp

and it emits electrons which are rapidly drawn to the target by the high voltage

across the tube. Surrounding the filament is a~small metal cup maintained at

the same high (negative) voltage as the filament, it therefore repels the

electrons and tends to focus them into a narrow region of target called

14

t

Fig.III-l Cross-section of sealed-of filament x-ray tube

15

focus them into a narrow region of target called the focal spot. X-rays are

emitted from the focal spot in all directions and escape from the tube through

beryllium windows.

The radiation escaping from beryllium windows consist of:(

(I) Brcmestrahlung radiation which is abroad band of continuos radiation

produced by the electrons from the filament converting their kinetic energy into

X-rays when colliding with the atoms of the target.

(II) Characteristic radiations, which are number of discrete lines of varying

intensity representing the energy released by rearrangement of the orbital

electrons of the atoms of the target following the ejection of one or more

electrons during the excitation process. These lines are known as K, L,

M lines, the type of the line produced is determined by the orbital electrons

taking part in the arrangement [fig. (III.2)]

(IH-3) THE X-RAY GENERATOR :

The generator is a Siemens-K710 generator? Jt^supplies the X-ray tube s\

with negative polarity high voltage from 20 KV to 50 KV and a current of 5

mAmp to 40 mAmp.

It can function with any X-ray tube requiring a negative high voltage and

with a nominally rated filament between 5 V and 12 V. The generator has many

built-in protection circuits to monitor filament over or under current, X-ray tube

over voltage and over current.

Cooling water monitor for the protection of the X-ray tube, along with

many built-in temperature and circuit parameters monitor for the protection of

the generator.The generator water flow monitor is a factory set up to audibly

• warn and then shut the generator when the cooling water flow drops below 4

liters/min. for 10 seconds. The generator has a digital display for indicating tube

high voltage, tube anode current, tube filament current.

16

(III-4) THE X-RAY III BE :

The X-ray tube used in the system is FK 60 Cu anode type with the

following specifications Kx wave length of 0.1542 NM, excitation voltage of 9.0

KV, Ni Kp filter, operating voltage 25 KV- 45 KV (Siemens D500 / 501

diffractometcr manual, 1985)

(IH-5) THE COOLING SYSTEM :

The cooling system unit CKULVER is delivered with all componejTj of the

cooling circuit such as circulating, pump, vaporization cooler, temperature

controller, temperature monitor, storage tank, safety valve for maximum

pressure limiting and connecting leads readily installed in such away that keeps ' S

and maintains the X-ray generator from over heating.

(1II-6) MONOCHROMOTIZATION :

A monochromatic beam of X-rays is desirable for certain diffraction

studies, when the sample is a powder one. The reason for this is that the Kp

component of the beam is sufficiently intense to produce its own diffraction

pattern. When this is superimposed on the Ka pattern, the difficulty of

interpreting the diffraction effects is materially increased.

The absorption effect offers means of moving the unwanted radiation to

leave a beam that is essentially monochromatic. The Nickel element (Ni) has an

absorption edge of I 49A°, which is intermediate between the wave length of

CuK«(1.5412A°) and Cu Kp(l .3922A°) radiation. This element is, therefore,

relatively transparent to the a-radiation and absorbs the P components of X-ray

beam and it can also reduce the intensity of the continuos spectrum. In this work

ci Ni filter with a Cu radiation is used.

17

M shell

///// L ^ ' i i ; i i "VV$S

K a i

Maximum electron energy

I V

Electrons

Ka,

Characteristic line spectruifrom Cu

Continuous spectrum

1 Wavelength X (A)Kp 1.3922

Ka, 1.5405Ko2 1.5408

Fii».lll-2 I lie generation of X-rays of a line spcotmm of copper due to tho transfer of

electrons into the K shell.

IR

(II1-7) THE GONIOMETER :

The D500 Siemens goniometer is constructed according to the Bragg-

Brentano para-focusing condition. The three components of primary interest

[fig(111.3)] are the anode of X-ray tube (B) emitting X-rays/ radiation, the >(

specimen carrier (P) in which r.he sample! be measured is placed and the y(

deiector (D) to pick up X-rays emanating from the sample.

In usual operation as a powder diffractometer, the X-ray hitting on the

sample diffract off the crystalline structure of the sample and cause peak

intensities to be recorded by the detector at the Bragg angle.

The goniometer is automatically controlled by DACO-MP which will be Xj ' \

described later.

(III-8) THE DETECTOR:

The detector used is a scintillation detector with a Nal(Tl) crystal 25 mm

diameter, approximately .1 mm thick .has a Beryllium window ,0.2mm thick,

a positive operating voltage of 1200 to 1300V, a maximum permissible voltage

of 1600V and a dead time < 10"6 second [Siemens D500/501 diffractometer

manual, 1985 ] .

Most of the X-ray quanta imping, on the scintillation crystal, are observed

by the crystal. The light flashes formed in the crystal cause a number of

electrons to be released from the directly coupled cathode of the multiplier .

The number of these electrons is greatly increased by multiplication at the

dynodes. The current pulse occurring at the anode when a quantum is

measured is ted, after amplification, by a charge sensitive pre-amplifier to the

compact measuring channel.

19

180"

/' 1)1. 1

I

\

B Focus of the x-ray lubeBl.I,Il,]II Aperture diaphragms1

BI.IV Detector diaphragmD DetectorKfl K/J fillerP Specimen

I

3 Glancing angle2S Diffraction angle

cp Aperture angleM Measuring circleF Focusing circle

Fig. 111-3 Focusing geometry of the diffractometer in case of 20/0 operation.

20

(IH-9) THE DACO-IYU':

• The DACO-MP is a micro-computer with standard controller interfaced to

: the Siemens D500 diffractometer. It has 32 Kbytes ROM and 23 kbytes of

; RAM. ll controls the diflractomctcr and the ditector while measuring. The

DACO-MP is connected to a printer which gives the out-put as a graph of

y intensity of diffracted rays versus 20 where 0 is the glancing angle and the

i corresponding d- spacing value.• . *

t The DACO-MP firmware is logically made up of seven tasks that may

I potentially run in parallel :

1) The sequence of analytical program stored in a memory.

:, 2) The completion of time consuming commands.

f; 3) The initialization routings for commands from Ihe computer.

4) The computer input processor task.

5) The error message output task .

% 6) The display up data task .

% 7) The local terminal input processor and command initialization task.

;jjg Ihese tasks are controlled by the type of command used for performing

certian work. Bach command is associated with fixed flag sets, one for the par

command and the other for the command of one or more explicit arguments .

There are four buffers in the DACO-MP user RAM :

1) instruction buffer ( 1-buffer) .

2) Data buffer ( D-bulTer) .

3) Register buffer ( Regs ).

4) Secondary memory

[DACO- MP USER'S Reference m a n u a l ^ . I , V2.2 ,1985]

(III-IO)SAMPLE PREPARATION AND SEPARATION:

The following/ procedure was used to separate the clay fractions (< 2 k

micron) needed tor XRD analyses :

a) About 10 gin of broken sample was dispersed in distilled water and then

disaggregated in a porcelain mortar.

b) Disaggregation was done gently and carefully without any grinding.

c) Hard samples were, further, disaggregated in the shaker and the

ultrasonic.

d) After the sample was disaggregated and brought into suspension, the

clay fraction (< 2micron ) was separated by the centrifuge at 2000 rotations per

min. for two minutes.

e) the clay fraction was filtered out from suspension by sucking filter, andi

allowed to dry in the oven at 50 °C.

g) from the dry clay fraction oriented mounts were prepared on glass slides

for XRD analyses.

(III-ll) DATA COLLECTION :

The data collection was carried out using a program called Analyses. Fig.

(III.4 ) is a flow chart of that program.

The out put of the program is a graph of position (measured in

degrees)versus intensity ( measured in counts per seconds) with the d-spacing

measured in A°.

The XRD analyses were carried out for all samples under the following

treatments :-

1) Normal samples ( air-dried ).

2) Ethylene glycolated sample for 24 hours.

3) Heating to 550 °C for 4 hours.

Y

I/PSA,EA.SS.CT

X-S.Y-S

Y

OPENWINDOW

Y

I/P

PW

Y

i/PTITLE

RUNOVERSHUT WINDOW;

RL:ADYFORXO

= Initialize

s Memory PartitionSA = Start AngleEA = End AngleSS = Step SizeCT 2 Counting Time

XS = X-ScaleY-S 3 Y-ScaleSR s Sample ReferencePT • Peak TablePS s Peak Search

PW = Peak WidthCD H Check DataXO s Extended OperationSM s SmoothingPS = Background SubtractionKS = K a o Stripping

"DATA ARE

SMOOTHED

ONLY"

Y

N

/ " DATA ARE

/ SMOOTHED AND

"I BACKGROUND

/ SUBTRACTED"

f DATA ARE SMOOTHED,

Y /AND BACKGROUND

SUBTRACTED AND Ka

STRIPPED"

('"SORRY NOANALYSIS

'WERE MADE"/

C END J

111-4 DACO-MP analysis program flow chart.

m

In all treatments the scanning parameters are the same except for the starting

angle of the glycolated one where the 20 = 2 is used because the glycolation

shifts the d-spacing to lower position.

The imput parameters Cor scanning arc :

1) A title.

2) Starting angle 5°.

3) End angle 35°.

4) Step size 0.05.

5) Counting time 2 seconds.

6) Peak width 0.14.

7)X-sca!e 2° per cm.

8) Y-scale 100 counts per seconds.

(IH-12) DATA PROCESSING

1) Peak Search

DACO-MP detects the peaks of the intensity curve and the important

parameter for detecting a peak is the peak width ( Pkw). The peak width is

defined as the length of the interval placed symmetrically around each point in

order to compute its polynomial . The ( Pkw) value is given in degrees.

The peaks to be recognized should match the following condition (Getting

started with DACO-MP V2.1, V2.2, 1985)

1/2 ( FWHM) < Pkw < 2 ( FWHM )

Where FWHM is the chord of the peak at the relative intercept level The

number of points placed symmetrically around each data point is the integer

closest to ( Pkw / Slcp size ) . This integer is bounded to lie between 1 and

15. In some extreme situations, the adaptation of peak width will not be

possible because of the inadequacy of the step size.

2)The Kxrended Openi lions

The extended operations are, the curve smoothing, background subtraction

and K ri stripping. These operations are done to obtain good results and

analyses.

The argument called (Smol) is the interval for the curve smoothing

operation. The number of points placed symmetrically around each data point is

the integer closed to ( Smol.'Stepsize) .This integer is boundejjl'to lie between 1 •*,.

and 1 5. For each data point, a third degree approximation of the diffractogram is

derived from these points, and the point under consideration is replaced by the

coefficient of power 0 of the computed polynomia.(Getting started with

DACO-MP V2.1, V2.2, 1985)

The second argument As' called ( Pkg2 ) is used to adjust the background V

subtraction algorithm. Let Y(20) be the equation of the convex, linear by parts,

envelope of the diffractogram, the continuous background B(2B) is then

estimated to be

0(20) = Y(20) - Bkg2. [Y(20)] Yl

The third argument called (Smo2) is the interval used to control the Kn 2

stripping algorithm . This algorithm is/work^ or a third degree least squareis [works' (

approximation polynomia computed on a fraction of the diffractogram. The

length of this fraction is derived from (Smo2) as done with ( Pkw) and ( Smol )

for the peak search and for the curve smoothing. The Ka 2 stripping algorithm is

derived from the Rachinger method (Getting started with DACO-MP

V2.1,V2.2, 1985)

In this work the smoothing and the background subtraction are used since

the information gain is enough for the determination of the samples components.

CHAPTER IV

RESULTS, INTERPRETATIONS AND CONCLUSIONS

IV.1 Introduction :

This chapter presents the the results of clay minerals analyses of samples

investigated. Moreover, the clays were identified qualitatively and semi-

quantilatively. It also discusses the various factors controlling the clay mineral

types and their distributions.

* IV.2 Nature and crystal structure of clays :

Clay minerals are described as a hydrous aluminum silicates with a sheet

I or layered structurejthey are pivyilosilicates. The sheets of a clay mineral are of X,

two basic types. One is a layer of silicon-oxygen tetrahedral with three of

oxygen atoms in each tetrahedron shared with adjacent tetrahedron and linked

together to form a hexagonal network (fig. I V.I.a). The second type of layer

consists of aluminum in octahedral coordination with O"2 and OH"1 ions.

There are two basic groups of cirys, Kandite group and smectite group.

Kandite group have two layered structure consisting of silica tetrahedral sheet

linked to an alumina octahedral sheet by common O/OH ions (fig. IV. 1 .a). No

change in Kandite structure or transformation. Smectite group have a three

layered structure in which an aluminum octahedral layer is sandwiched

between two layers of silica tetrahedral (fig. IV. 1). The typical basal spacing is

14 A0 but smectites have the ability to adsorb water molecules and this changes

the basic spacing, it may vary from 9.6 to 21.4 A0 (Tucker 1992).

The common member of Kandite group is Kaolinite (K), its d-spacing is 7

A0. Other ciay minerals with three layered structure are Illite(I) and

Chlorite(C). Smectite have d-spacing of 14 A0, illite 10 A0 and chlorite with d-

spacing of 14 A0. Th'iie are mixed layer, clays between illite and smectite.

7 *(C),-Smectite have d-sn.ae'ing of 14 A^ittile 10 A0 and''chl«jrite>ntlf d-spacing y-y

f 14 ,-There are nfixed kiyerj^tfys between iJJrfe and smectite.

(VI-3) Method Of Interpretation : \

To identify the clay minerals we have three runs (discussed in Ch.III) , the \

normal, glycolated and heated. The four principal clay minerals gives/certain d- X .]

spacing in the nonnal run. Kaolinite ha.c d-spacing 7A°, illite 10A°, smectite 12-

15 A0, chlorite 14 A0 and mixed layer between smectite / illite has intermediate

of high values of d-spacing (Tucker 1992). Because smectite and chlorite have

the same range of spacing we look in the glycolated run to distinguish between

them, smectite expands to d-spacing of about 17 A0 but chlorite remains as it is.

To give further distinction we must look at the heated run,we see that smectite f

collapses to 10A° and kaolinite is destroyedJTable IV. 1 shows the d-spacing of

any clay in different runs. (Thorez 1976).

The clay minerals types were identified qualitatively and semi

quantitatively according to Thorez(1976).

The percentages of the clay minerals were calculated from the length of

the peaks. The sum of the peak lengths of the clays is 100% , except the length

of Kaolinite which is divided by three and then added to the others, this because

Kaolinite grows rapidly three times faster than the other clay minerals (Thorez

1976).

( IV. 4) XRD Results :

Table IV.2 gives the depth of each sample and the percentage of the four

principal clays and mixed layer Sm/l for all samples. The starjiboye the peak A

means that the beak cannot seen clearly by the defector. Fig. IV.3 gives the / \

vertical distribution of clay minerals. Figs. 4 to 19 are the charts of the measured

samples. N, G and H refer to normal, glycolated and heated one respectively .

27

(IV. 5) Interpretation , Discussion and conclusion :

If we divide the samples into zones according to their depth , upper from

1524 to 2743 m. middle 2743 to 3353 m and lower 3353 to 4572 m, its clearI*?

that from table IV. 1 the main clay in the samples is Kaolinite. Smectite is more /)/

abundant in the upper zone and it decreases in the middle and lower ones. Illite

percentage is lower in the upper zone, increases at the middle and the lower

one. In all zones there is a mixed-layer of smectite/illite. Chlorite increases in

the middle and lower zones but it decreases in the upper one.

The origin of clay minerals is attributed to three processes (a) inheritance

from detrital source, (b) neoformation (c) transformation by burial diageneses

(Tucker, 1992). Therefore, clay minerals may indicate environmental,

diagenetic, source rock and climatic influences (Chamley, 1989).

The vertical changes in clay mineralogy in the Muglad basin with the

increase in depth most probably reflects the effect of buriaf diagenesis. which

takes place principally through the rise in temperature accompanying increased

depth of burial (Chamley 1989). That is the main change is an alteration of

smectite to illite and chlorite via mixed-layer clays of smectite-illite and

smectite-chlorite (figs. IV.2, IV.3). This change usually occurs around 2-3km

between 70- 95 °C. The above depth and temperature conditions are provided

in the Muglad basin (fig.IV.3, fig. IV.2). The higher percentage of illite and

chlorite in the lower zones indicates the effect of burial diagenesis

(Tucker, 1992). Ramseyer and Boles (1986) reviewed the importance of the

various controlling factors on smectite transformation during burial, such as

temperature, potassium availability, inhibtor ions, permeability, smectite

composition and the residence time. Other studies, however, have indicated

that temperature is one of the principal factors in the transformation of smectite

during burial diagenesis (Hower et al., 1976; Burtner and Warner. 1986).

28

The depth of burial of the sediments studied is more than 4500 m which is

quite sufficient to allow deep diagenetic processes to operate under the given

depth (4500m) and average geothermal gradient of 30 °C/km. Large part of the

sediments section must have been subjected to temperature greater than 100

°C (Fig.IV-3). Such burial diagenetic influences have been reported from the

Muglad basin (Abdullatif and Barazi, 1993).

Moreover, the high kaolinite abundance indicates the predominance

pedogenic processes over direct-rock weathering. This should testify to intense

chemical weathering and leaching under rather warm humid climate that

prevailed in the Muglad basin during most of the Cretaceous time. It is most

probably that the large proportion of the kaolinite encountered could have been

inherited through detrital from source rocks which subjected to intense

weathering. The high content of smeotite in the upper sediment section may

reflect dryer climatic intervals, limited hydrolysis and leaching (Chamley,

1989). Similar situation applies to the limited content o*fillite and chlorite.

Furthermore, this interpretation cannot exclude folly the partial formation of

some of the clay minerals encountered through neogenesis or neoformations,

since the physio-chemical and environmental conditions were favourable

(Chamley, 1989).

( ) anif ;."• ' O^O"1" Honn " amf • Silicon alolnj O Aluminnin.

8 0. kanlimla AljOj 2S.0, ?H?0

nlimiiM.i i

li.is.il f.p.Tci'M) 7A

basic loirnul.v 7AljO, 8ScD, 711,0 nil,O

oniM |M(j. CtlU AI,O, !>r,.O, «H,

much Mjfi'hl'itinii ofM by Mq AIM! f r

tuil r>n.iiid^blt from9 G 10 21 1 A

H,0 M,0

illila KAIjtOlM, lAlgijlO. 0M|, 0 |

OM K"

K'

mtlKhliilinn nl Si UyAl in silica Inycrit

inlC'lAyer K' tr>pnlliRrw.lh some OM . re and Mg

basnl tpacing 10 A

K" K' ~ f » / M g

cliloiit*

Sul»<ti(u(ion of A| Uy ft

b'ur.itc Uyei$ (Mg OM)hnlvvflftu Al -Si shfiftti

basat tp^dng.14 A

Fig. IV-l Diagrams illustratiitg the structures of clay minerals

30

Imrtnl

bmi.il

ilhlo

yslalliniiyl

scrccife mulchloiiln

Fig. IV-2 Diagram ilhi.strating the changes of clay minerals with increasing

depth of burial and into mctamorphism

50°C

1&28 Jp:V

90°C2134

Clay mineral %10 20 30 IQ 50 60 70 frp 9Q 100

2638 .;..;;.;;>.»:.VoVi-v:-4.

2 743 ^ . ^ ^ J f T ^

S 30A81 13(fC

J C

CL

o

3353 '

3658

3962

150°C4262

4572

o o * ^ 0 0 p o oo o o o ©

O ° o O O °oo c? o 0 o u o ° °

o _O OO.

II

K I OOOff Sm -Sm/I S C

Fig. IV-3 vertical distribution of clay minerals

3.:

Table IV-1

Summary of behaviours of the clay minerals towards identification

treatments

Kaolin ile

d spacing in ASYMBOL 7 B 9 10 11 ' 13 13 M 15 1« 1?

K NEG

Swelling Chloiile Cg

III,io

Smeclilcs(Monlmo'illoniles)

NEG500

500

NEG500

N500

EG

EG

Vflfiniculile 500 IMEG

PAL

500

NEG

Sopiolile SEP 500 NEG

Values ol lite bnsnl r^ll^clmn in cl(A). lor the current clay minerals, after Ihe classical idenliliolion essays (N •• nulural.unlreslcn1 sample ; EG - elliylone glycol ; 500 - hnnling lo 500"C).

33

*4 Table (IV.2) Clay mineral types percentages in samples measured .

'-A

No

1

2

3

4

5

6

7

8

9

10

11

12

13

Depth inmeters

1603

2243

2344

2499

2646

2682

2890

3030

3167

3386

3790

4252

4590

Smectite%

76.5

—

11.55

—

35.5

—

28.57

—

25.0

37.51

—

21.5

—

lllite %

7.65

27.9

11.55

23.1 ...

13.47

23.1

21.4

24.4

16.6

26.79

11.1

32.25

27.3

Knolinite%

15.8

23.1

53.8

46.1

50.2

34.6

50.0

43.1

33.3

24.97

22.2

35.48

72.7

Chlorite%

—

—

23.1

—

—

23.1

—

32.5

25.0

• 10.71

33.3

10.75

Smectite/lllite %

—

48.91

—

30.0

—

19.2

—

—

---

33.3

—

—

34

no-:.

+ - • ; ' • • : • • -

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3.9141 28.

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35 3.2397. 832.

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Fig.VI-4 sample no.l-N

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36

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REFRENCES

1- Abdullati£ O. M. and Barazi, N. (1993). Sedimentalogy and maturityevaluation of the NW Muglad and Nile Rift basins, Sudan. In Thorweiheand Schandelmeier(eds.). Geoscientific Research in NE Africa. Balkema.

395-399.

2- Alexander O.E Animalu (1977), Intermediate Quantum theory ofcrystalline solids. Prentice - Hall, Jndia^ 11 5 | ^ | ^ ^ v. ^ , «**-

3- Burtner, R. and Warner, M.A. (1986).Relationship betweenillite/smectite diagenesis and hydrocarbon generation in lower t? - ,-Cretaceous Mo wry and Skull Creek shalesi of tKe^ofthen Rock *Mountain area. Clays and clay minerals, v34, No.4, p.390-402.

4- Carol, D. (1970). Clay Minerals: Aguide to their x-ray identification.Geological Society of America, special paper 126.

5- Chamley, H. (1989) Clay sedimentoiogy, Springer - Verlag, Berlin623 pp .

6- Cullity B.D, (1978), Elements of X-ray Diffraction, second edition,Addison - Wesley Publishing Compciny .

7- DACO - MP User's V2.1 , V2.2 manual (1985). •

8- DACO - MP Getting start manual V2.1 , V2.2 manual (1985).

9- Diffrac -AT V3.1 Start up manual (1992).

10-Hower, J., Elsinger, E.V., Hower, M.E. and Perry, E.A.(1976) . Mecha- -nism of burial metamorphism of argillaceous sediments: 1,mineralogical and chemical evidence, Geological Society of AmericaBull., V.89, p.725-737.

11-Idris, Hassan H. (1994). X-ray diffraction studies of clays andminerals Msc. Thesis, Dcpt. of Physics, U. of K.

12- Klug, H. And Alexander, L. E., (1974), X-Ray diffraction proceduresfor polycrystallijie and amorphous materials , Second edition, John Wiley& Sons, Inc.

13- Ramseyer, K. and Boles, J. R. (1986). Mixed-layer illite/smectiteminerals in Tertiary Sandstones and Shales, San Joaquin basin,California. Clay and clay minerals, V.34, No.2, 115-124.14- Siemens D500 , D501 diffractometer operating instruction manual,Model No. 79000- B3400 - C042-10 (1985).

15- Thewlis J., Hughes D.J. and Meetham A. R.(1962), EncyclopaedicDictionary of Physics.

16- Thorez, J. (1976). Practical Identification of Clay minerals. EditionsG. Lelotte, Dison Belgium.

17- Tucker (1988), Techniques in Sedimentology, Black well Scientificpublication Oxford 0X2 OEL 8 John street.

18- Tucker (1992), Sedimentary Petrology, An introduction to the originof sedimentary rocks , Black well Scientific publication Oxford O&2

OEL 8 John street.

19- Zussman, J. (ed) (1977). Physical methods in determinativeminerology (second edition), Academic press.