chapter 2 methodology 2.1 introduction
TRANSCRIPT
CHAPTER 2
METHODOLOGY
2.1 Introduction
To accomplish in this study, observation and description of Quaternary strta
and sediment samples collection in the field and laboratory analysis on the samples
were importance. The field methods include surveying, lithostratigraphic study,
sample collection and fossil collection. The purposes of surveying is to measure the
depths and position of sediment sections in the study area using topographic map and
global positioning system instrument. The careful study of lithology and sedimentary
structure allowed determining depositional environment. The sediment samples were
analyzed for grain size distribution, mineral composition, lithostratigraphy and fossil
were used to interpret the palaeoenvironment.
Laboratory methods include grain size distribution analysis, grain shape
analysis, total organic carbon analysis, heavy minerals and light minerals analysis, x-
ray diffraction analysis and 14C age dating determination. Grain size distribution
studies include sieve analysis both dry sieve and wet sieve for sand up to gravel size
and mud size were used pipette method. Grain shape analysis, especially sphericity
and roundness were analyzed by binocular microscope. Total organic matter study
was analyzed by loss on ignition (LOI) method and convert to total organic carbon
values. Heavy minerals and light minerals were separated by gravity separation
method and identified by optical properties using binocular and polarizing
microscope. The mineralogy of the mud fractions were determined by x-ray
diffraction method. The mineral determination under heavy mineral and light
minerals analysis and x-ray diffraction analysis allowed interpreting the source rocks
and the diagenetic processes. Fossils, wood fragments and leaf fragments, were
determined for age dating by 14C dating method, which lead to understand the age of
sediment layers in the study area.
� 16
2.2 Field surveying method
The sand pit in the study area has been surveyed by measuring its size,
dimension and elevation using global positioning system instrument, compass and
measuring tape. Data of nine locations of the border of sand pit are shown in table
2.1. The area of study area was calculated by dividing the study area into seven
triangles and calculating the area of each triangle from the angles and distances is
shown in Figure 2.1. Calculation based on Heron’s formula.
where
a, b and c is the distances of triangle
From the computation by using Heron’s formula, total area of the study area is
184,802.31 m2 (115.50 Rai).
2.3 Lithostratigraphy and sedimentary characteristics
2.3.1 Stratigraphy
A common system of stratification terminology was purposed by McKee and
Weir (1953). In this system, a lamina is a stratum less than 1 centimeter thick and a
bed has a thickness greater than 1 centimeter. Layers oblique to bedding surfaces are
cross-strata. Basic measurements are dip and strike direction of each structure for
interpreting palaeocurrent directions. The sediment features within each stratum are
its facies.
� 17
Table 2.1 Station elevation and UTM coordinates.
Figure 2.1 The study area was reconstructed by UTM coordinate data.
Station Elevation
(meters above mean sea level)
Position
(UTM zone 47)
N E
A 3.20 1624595.00 659189.00
B 3.10 1624625.00 659489.00
C 2.90 1624690.00 659494.00
D 3.50 1624696.00 659655.00
E 1.60 1624943.00 659613.00
F 1.80 1624945.00 659556.00
G 4.30 1625056.00 659475.00
H 3.30 1625069.00 659252.00
I 1.80 1624809.00 659116.00
� 18
2.3.2 Sedimentary facies analysis
The study of sedimentary facies is an important tool for recognizing
depositional processes, sedimentary environments and sedimentary evolution. Facies
types are described by employing a hierarchical scheme. The scheme used in this
study is the one suggested by Miall (1977). This scheme recognizes three major
grain-size classes, gravel, sand and fines, each of which may be further subdivided
according to texture and style of bedding and lamination.
One characteristic structure of sediments is cross-stratification. Two systems
are used for classifying and describing cross-stratification. The one purpose by
McKee and Weir (1953) is simple but it is less complete than the classification of
Allen (1963) that attempts to include all major factors that may be encountered.
These systems recognize three main types of stratification:
1. Simple cross-stratification are represented by non-deposition or a change in
character.
2. Planar cross-stratification consisting of sets whose lower bounding surfaces
are a plane surface of erosion.
3. Trough cross-stratification consisting of sets whose lower bounding surface
are a curved surface of erosion.
There are two kinds of cross-strata based on shape: lenticular-set and wedge
set. Cross-stratification is small scale if it is less than 30 centimeters in length,
medium scale if it is between 30 centimeters and 6 meters in length and large scale if
it is more than 6 meters in length. The stratification dip divides the cross strata into
high angle, 20 degrees or more and low angle, less than 20 degrees.
2.3.3 Sediments sampling
The locations of stratigraphic sections (section 1 to section 5) and fossils were
determined using global positioning and measuring tape (Figure 2.2). The elevation
of sediment profile was determined. Sample location, sediment strata and fossils
� 19
Figure 2.2 Location of stratigraphic section (S1 to S5) in the sand pit of study area.
were photographed. The samples were collected, interval 30 centimeters each
sample, along vertical profile (Figure 2.3). One hundred and eighty-three samples
were collected and analyzed. Twenty-six samples were selected to determine by x-
ray diffraction method. Sixty-one fossil samples were collected from sediment layers.
2.4 Grain-size analysis
The purpose of measuring grain-size distribution is to classify sediments.
Various depositional environments tend to be characterized by distinct grain-size
distributions that can be used for statistical interpretations. Grain-size was based on
the Wentworth scale (Wentworth, 1922). The size classes used were boulders,
cobbles, gravel, sand, silt and clay (Figure 2.4). The frequency distribution of the
� 20
Figure 2.3 Samples collection in the sand pit, Shows sediment and horizon layers.
Figure 2.4 Udden-Wentworth grain-size scale for siliciclastic sediment (Wentworth,
1922).
� 21
weight or number of particles per size class tends to follow approximately a log
normal distribution when particles size are expressed metrically in millimeters.
Krumbein (1934) expressed particle size D as the negative logarithm to the base of 2
and called the result the �-scale. Particle sizes in �-unit were converted from particle
D size to units of millimeters by:
where D is the grain diameter in millimeters unit
2.4.1 Size analysis
One hundred and eighty-three samples from five stratigraphic sections at Ban
Beok sand pit were analyzed for their distribution of grain sizes. One hundred and
sixty-six mud fraction dominated samples were weighed estimation in 60 g and
transfer into glass that contain water. Seventeen sand fraction dominated samples
were transferred in metal pan and dried in oven at 40 �C. Drying time was just
overnight. Drying at high temperature causes in grain dispersion (Carver, 1971). Each
dry sample was divided into 150 g by riffle splitter. All samples were wet-sieved to
separate sand and gravel fractions from silt and clay fractions. Sand and gravel
fraction was analyzed and separated into each grade by dry-sieve method. Silt and
clay fraction was determined grain size based on gravity settlement by pipette
method.
2.4.1.1 Wet sieving method
All subsamples would normally be dealt during this procedure.
1. Set equipment used for wet sieve (Figure 2.5).
2. Transfer sample on the 63 �m sieve mesh.
3. Using the wash bottle containing pure water rinse the sample in sieve screen
until the water is clear as it runs into the cylinder.
� 22
Figure 2.5 Arrangement of equipment for wet sieve method.
4. Washing the underside of sieve screen and funnel into the cylinder.
5. Transfer sample on the sieve mesh into the receiver.
6. Place the cylinder that contain fine fraction sample in the safety area.
2.4.1.2 Particle-size analysis of sand-grade material by sieving
Samples would normally be dealt with simultaneously during this procedure.
1. Transfer all the samples to the tray and allow it to air-dry.
2. If the sample contains a significant proportion of plant organic matter, this
should be removed before weigh sample.
3. Label and weigh sample to 0.01 g.
4. Remove silt and clay-grade from sand and gravel-grade for pipette analysis in
wet sieve technique into 1000 cm3 cylinder.
5. Place the sample after step 4 in the oven until samples are dry.
6. Assemble a set of sieve at half phi-unit intervals from 0.063 millimeters to 4
millimeters. Check that each sieve is clean (Figure 2.6).
� 23
Figure 2.6 Arrangement of equipment for dry sieve method.
7. Stack the sieve in order from coarsest down to finest, place the receiver at the
bottom of stack.
8. Pour the dried sample onto the top of stack and the lid on the sieve stack and
clamp the stack firmly into the sieve shaker.
9. Sieve for 15 minutes.
10. Remove sieve stack from the shaker.
11. Take the coarsest sieve on sieve stack onto the paper and remove the sample
that retained on sieve into the container.
12. Label and weigh sample in container to 0.01 g.
13. Repeat the procedures in step 11 and 12 for each successively finer sieve in
the stack.
14. Materials that have passed into receiver should be weighed and added to the
remainder of silt and clay-fraction obtained in step 4 for pipette analysis.
� 24
2.4.1.3 Particle-size analysis of silt and clay-grade material by pipette
analysis
The pipette analysis is based on the principle that particles will settle in a fluid
at a rate dependent upon their size, shape and density and upon the density and
viscosity of the fluid (Gale and Hoare, 1991). To simplify this relationship, it is
normally assumed that the particles involved are spheres with a density equal to that
of quartz (2650 kg m-3). Particle size as determined by sedimentation analysis is
expressed in terms of hydraulic-equivalent diameter. This method is not practicable
to determine the hydraulic-equivalent diameter of coarse particles.
The terminal settling velocity of small sphere in a fluid is given by Stokes’
Law.
where � terminal settling velocity (m s-1)
� � � particle density (kg m-3)
� � � fluid density (kg m-3)�
� � g acceleration due to gravity (m s-2)
� � D� spherical particle diameter (m)�
� � �� fluid dynamic viscosity (kg m-1 s-1)
If the sample of particles is dispersed evenly throughout a fluid, the velocity of
particle settling will be determined from Stokes’ Law. Assuming the fluid within
which settling take place to be pure water of known temperature, it is possible to
calculate the depth and time of sampling necessary to sample only particles finer than
a given size (Tables 2.2 and 2.3).
� 25
Table 2.2 Depth of pipette insertion and time of withdrawal for 25�C (from Folk,
1974).
Depth (cm) Phi unit Diameter (mm) Time of withdrawal
20 4.0 0.063 20 sec
20 4.5 0.044 1 min, 45 sec
Remix suspension
10 5.0 0.031 1 min, 45 sec
10 5.5 0.022 3 min, 28 sec
10 6.0 0.016 6 min, 58 sec
10 7.0 0.008 28 min
10 8.0 0.004 1 hr, 50 min
10 9.0 0.002 7 hr, 30 min
5 10.0 0.001 15 hr
Table 2.3 Method of sampling various size fractions by varying the depth of pipette
insertion. Depth given for a range of temperatures (from Folk, 1974 and
Lewis, 1984).
Temp
(�C)
Total
suspension
4.5� 5.0� 5.5� 6.0� 7.0� 8.0� 9.0� 10.0�
20 sec 2 min 4 min 8 min 15 min 30 min 2 hr 8 hr 32 hr
18 20 19.8 19.7 19.8 19.6 9.8 9.8 9.8 9.8
19 20 20.2 20.1 20.2 20.0 10.0 10.0 10.0 10.0
20 20 20.7 20.6 20.7 20.6 10.3 10.3 10.3 10.3
21 20 21.3 21.1 21.3 21.1 10.5 10.5 10.5 10.5
22 20 21.8 21.6 21.8 21.6 10.8 10.8 10.8 10.8
23 20 22.3 22.1 22.3 22.1 11.1 11.1 11.1 11.1
24 20 22.8 22.7 22.8 22.6 11.3 11.3 11.3 11.3
25 20 23.3 23.2 23.3 23.2 11.6 11.6 11.6 11.6
26 20 23.9 23.8 24.0 23.7 11.9 11.9 11.9 11.9
27 20 24.5 24.3 24.5 24.2 12.1 12.1 12.1 12.1
� 26
Stokes’ Law is only applicable to particles less than �60 �m in diameter
(Allen, 1983). The lower limit of measurement by pipette analysis is �2 �m because
effects of Brownian motion and convection (Allen, 1983).
In their natural state, fine particles tend to form aggregates or to flocculate into
chains and clusters. In laboratory, particles must be disaggregated and in which
individual particles are maintained in the suspension. Dispersion is usually achieved
by making up the suspension in a dilute solution of a compound, which builds up the
ionic charge on clay particles.
In this study, a 0.5% w:v solution of sodium hexametaphosphate ((NaPO3)6) is
used to disperse materials in suspension. This dispersant is recommended (Gale and
Hoare, 1991). Any reader requiring further information on flocculation and
dispersants is referred to Galehouse (1971) and the references therein. The following
steps should be performed for each subsample to be analyzed. Note that several
subsamples would normally be dealt with simultaneously during this procedure.
1. Weigh and label beakers to 0.0001 g.
2. Set up equipment for pipette analysis (Figure 2.7).
3. Add pure water in fine fraction sample cylinder to 1000 cm3.
4. Add sodium hexametaphosphate ((NaPO3)6) in fine fraction sample cylinder to
0.5% w:v solution.
5. Place cylinder of sample on non-vibrate table, away from direct sunlight and
other sources of heat.
6. Record the temperature of suspension.
7. Stir the contents in cylinder vigorously with the plunger-stirrer.
8. Remove stirrer from cylinder. When the stirrer emerges from suspension, start
the stop-clock.
9. In 20 seconds after stirring, insert the marked 20 cm3 pipette, to which is
attached the pipette filler, so that the tip is at a depth of 200 mm in suspension
and the pipette is centrally and vertically located in cylinder and draw up 20
cm3 of suspension into the pipette.
� 27
Figure 2.7 Illustration of the pipette method of grain size analysis for fine fractions.
10. Withdrawn the pipette from cylinder and deliver the contents of the pipette
into the labelled beaker.
11. The next pipette sample should be taken following the same basic procedure.
Sampling time and depth of draw up suspension are given in Tables 2.2 and
2.3.
12. After the second sample has been taken, the suspension should be restired and
further samples taken following the procedure outlined in step 8 and 9.
� 28
13. After final sample has been taken, placed all beaker and its contents in the
oven for removed water and moisture from the sample.
14. Weigh dried-sample and beaker to 0.0001 g.
15. Calculate pure-weigh samples in each beaker.
2.4.2 Sedimentary nomenclature
Folk (1954) considered the textural and mineral compositions related to grain-
size and introduced two triangular diagrams. The first diagram provides a
nomenclature based on the major textural groups, using gravel, sand, silt and clay
(Figure 2.8). The second triangle is used to define ten sedimentary rock types and is
based on the mineralogy of the clay, silt and sand fractions (Figure 2.9 and Table 2.4).
2.4.3 Graphic parameters
Apart from sieving as a means for general sediment classification, ratio of
various particle distribution parameters can be used to distinguish between sediments
of different origins, transportation modes and duration or distance of transportation.
Particle-size distributions are commonly characterized by four distribution
parameters: mean; standard deviation or sorting; skewness and kurtosis. The 50
percent diameter on a cumulative frequency curve defines the median. In this study,
the distribution parameters were cumulated according to Folk and Ward (1957).
Mean size: The central tendency of grain-size distribution is of prime
importance in classification. It immediately provides an average size to which
Wentworth’s nomenclature can be applied. However, Folk and Ward (1957)
considered that this was not sufficiently accurate for bimodal and strongly skewed
distributions. Thus, they introduced:
� 29
Figure 2.8 The fifteen major textural groups as defined by the relative percentages of
gravel (grain size coarser than 2 mm), sand (grain size between 0.0625 to 2
mm) and mud (grain size finer than 0.0625 mm) (after Folk, 1954).
� 30
Figure 2.9 The ten major textural groups as defined by the relative percentages of
sand (grain size between 0.0625 to 2 mm), silt (grain size between 0.0039
to 0.0625 mm) and clay (grain size finer than 0.0039 mm) (after Folk,
1954).
� 31
Table 2.4 Twenty-two textural groups comparing unconsolidated and consolidated
sediments (after Folk, 1954).
Class Unconsolidated Consolidated
G Gravel Conglomerate
mG Muddy gravel Muddy conglomerate
msG Muddy sandy gravel Muddy sandy conglomerate
sG Sandy gravel Sandy conglomerate
gM Gravelly mud Conglomeratic mudstone
gmS Gravelly muddy sand Conglomeratic muddy sandstone
gS Gravelly sand Conglomeratic sandstone
(g)M Slightly gravelly mud Slightly conglomeratic mudstone
(g)sM Slightly gravelly sandy mud Slightly conglomeratic sandy mudstone
(g)mS Slightly gravelly muddy sand Slightly conglomeratic muddy sandstone
(g)S Slightly gravelly sand Slightly conglomeratic sandstone
M Mud Mudstone
sM Sandy mud Sandy mudstone
mS Muddy sand Muddy sandstone
S Sand Sandstone
cS Clayey sand Clayey sandstone
zS Silty sand Silty sandstone
sC Sandy clay Sandy claystone
sM Sandy mud Sandy mudstone
sZ Sandy silt Sandy siltstone
C Clay Claystone
Z Silt Siltstone
Standard deviation: Standard deviation is a measure of the spread about the
mean or width of a distribution. Distribution is the range of particle sizes within
which a preset percentage of all data are contained. It is generally used to describe
� 32
the sorting of sediment. Folk and Ward (1957) introduced the inclusive graphic
standard deviation as follows:
In addition, Folk (1954) assigned terminology to the Inman (1952) standard
deviations, as in Table 2.5. The same terminology is used for the inclusive graphic
standard deviation (Folk and Ward, 1957).
Skewness: Skewness is the measure of the symmetry of the distribution and is
quantified as zero in phi units for a symmetrical distribution. If the distribution is
skewed towards smaller phi values, this being coarser size, the phi mean is
numerically less than the median causing negative skewness and for a distribution
skewed toward the finer size, the skewness is positive (Figure 2.10 and Table 2.6). In
1957, Folk and Ward introduced an inclusive graphic skewness:
In cases where the sizes of the limiting percentiles are not available, these
formulae cannot be used.
Kurtosis: Kurtosis is a measure of peakness or the ratio of the average spread
in the tails to the standard deviation of the distribution (Table 2.7). Folk and Ward
(1957) introduced an inclusive graphic kurtosis:
� 33
Table 2.5 Folk and Ward (1957) classification of standard deviation values (after
Bunte and Abt, 2001).
Sorting Coefficient Characterization > 4 Extremely poor 2-4 Very poor 1-2 Poor
0.71-1 Moderate 0.50-0.71 Moderately well 0.35-0.50 Well
< 0.35 Very well
Table 2.6 Folk and Ward (1957) classification of skewness values (after Bunte and
Abt, 2001).
Table 2.7 Folk and Ward (1957) classification of kurtosis values (after Bunte and Abt,
2001).
Value Classification Explanation -0.3 to -1 Very negatively skewed Very skewed towards the fine side
-0.1 to -0.3 Negatively skewed Skewed towards the fine side -0.1 to 0.1 Nearly symmetrical Nearly symmetrical 0.1 to 0.3 Positively skewed Skewed towards the coarse side 0.3 to 1 Very positively skewed Very skewed towards the coarse side
Value Classification Explanation < 0.67 Very platykurtic Very flat frequency distribution
0.67-0.90 Platykurtic Flat 0.90-1.11 Mesokurtic Not especially peaked, normal 1.11-1.50 Leptokurtic Highly peaked
> 1.50 Very leptokurtic Very highly peaked
� 34
Figure 2.10 The shape of symmetrical, positively and negatively skewed frequency
distributions curve (after Bunte and Abt, 2001).
2.4.4 Particle-size frequency and cumulative frequency distribution
The result of a laboratory particle size distribution analysis is a record of
particle weight or particle numbers retained on each sieve. The weight per size class
is then entered into a sheet table for all subsequent computations.
1. Compute the percentage weight for each size class.
2. Plotted as a percentage frequency distribution histogram.
3. The percentage of particle weight or number of particles retained on each
sieve is converted into the percentage of particle weight or number passing the
next larger sieve opening size.
4. The particle size classes and the percent finer by weight are plotted together to
make a cumulative particle size distribution curve, also called the sieve curve
or the gradation curve.
2.4.5 Percentiles and their computation
Two sediment mixtures of different particle size are usually distinguished by
comparing several of the percentile values of the two distributions or the parameters
derived from the percentiles. A percentile is a sediment size indicated by the
� 35
cumulative distribution curve for a particular percent finer value. For example, the
sediment size for which 80 percent of the sediment sample is finer is the 80th
percentile. The notation is D80, where D represents particles size in millimeters and
the subscript 80 denotes 80 percent. D50 is the median point of distribution that
divides the distribution into two equal parts. The particle size for which 25 percent of
the distribution is finer is the 25th percentile, or D25. D25 and D75 are called quartiles.
Theoretically, any percentile value can be used for comparison, but, customarily the
particle size of D50, D25 and D75, D16 and D84 and D5 and D95 are used. In a normal
distribution, one standard deviation from the median encompasses all data between
D16 and D84 and is the point on a distribution curve at which the change of curvature
occurs. D5 and D95 characterize the distribution tails. Data between D5 and D95
comprise almost two standard deviations on either side of D50, or the median. These
seven percentiles may be compared as individual values or can be used to compute
distribution parameters, such as mean, standard deviation and skewness.
2.5 Roundness and sphericity
Particle forms are characterized by shape and angularity. Shape refers to the
ratio of the three axial lengths. Angularity refers to angular edges as opposed to
rounded surfaces. Particle form effect the area exposed to flow forces, drag forces,
lift forces and therefore, particle entrainment, transport and deposition.
The mode value of each sample was analyzed for roundness and sphericity.
The sand size particle is the major of the mode. Thus, the roundness and sphericity
were analyzed based on Powers (1953) to estimate grain roundness and sphericity
(Figure 2.11).
� 36
Figure 2.11 Illustration of roundness and sphericity of sediments grains based on
comparisons with grains of calculated roundness (after Powers, 1953).
2.6 Total organic carbon analysis
Organic matter in soils and sediments is widely distributed over the earth’s
surface occurring in almost all terrestrial and aquatic environments (Schnitzer, 1978).
Soils and sediments contain a large variety of organic materials ranging from simple
sugars and carbohydrates to the more complex proteins, fats, waxes, and organic
acids. Important characteristics of the organic matter include their ability to form
water-soluble and water insoluble complexes with metal ions and hydrous oxides;
interact with clay minerals and bind particles together; sorb and desorb both naturally-
occurring and anthropogenically-introduced organic compounds; absorb and release
plant nutrients; and hold water in the soil environment (Schnitzer, 1978). As a result
of these characteristics, the determination of total organic carbon is an essential part
of any site characterization since its presence or absence can markedly influence how
chemicals will react in the soil or sediment.
In soils and sediments, there are three basic forms of carbon that may be
present. They are elemental C, inorganic C, and organic C. The quality of organic
� 37
matter in sediments is critical to the partitioning and bioavailability of sediment-
associated contaminants (Schumacher, 2002).
The basic principle for the quantitation of total organic carbon relies on the
destruction of organic matter present in the soil or sediment. The destruction of the
organic matter can be performed chemically or via heat at elevated temperatures. All
carbon forms in the sample are converted to CO2, which is then measured directly or
indirectly and converted to total organic carbon or total carbon content, based on the
presence of inorganic carbonates. These methods can either be quantitative or semi-
quantitative depending on the process used to destroy the organic matter and the
means used for detecting/quantifying the carbon present.
The loss on ignition (LOI) method is semi-quantitative technique based upon
the indiscriminant removal of all organic matter followed by gravimetric
determination of sample weight loss. The determination of organic matter involves
the heated destruction of all organic matter in the soil or sediment. A known weight
of sample is placed in a ceramic crucible (or similar vessel), which is then heated to
between 350�C and 440�C overnight (Blume et al., 1990; Nelson and Sommers,
1996; ASTM, 2000). The sample is then cooled in a desiccator and weighed.
Organic matter content is calculated as the difference between the initial and final
sample weights divided by the initial sample weight times 100%. All weights should
be corrected for moisture/water content prior to organic matter content calculation.
LOI method temperatures should be maintained below 440�C to avoid the
destruction of any inorganic carbonates that may be present in the sample. One
concern with this technique is that some clay minerals will lose structural water or
hydroxyl groups at the temperatures used to combust the samples. The structural
water loss will increase the total sample weight loss leading to an overestimation in
organic matter content. One possible means to avoid this concern is through the pre-
treatment of the sample via removal of the mineral matter using HCl and HF acids
(Rather, 1917). However, the use of HCI may dissolve part of the organic matter
leading to an underestimation of the organic matter content and the potential use of a
correction factor.
� 38
Since these methods determine the organic matter content in the soil or
sediment, it is necessary to convert the organic matter content to total organic carbon
content. Traditionally, for soils, a conversion factor of 1.724 has been used to convert
organic matter to organic carbon based on the assumption that organic matter contains
58% organic C (i.e., g organic matter/l.724 = g organic C) (Nelson and Sommers,
1996). However, there is no universal conversion factor as the factor varies from soil
to soil, from soil horizon to soil horizon within the same soil, and will vary depending
upon the type of organic matter present in the sample. Conversion factors range from
1.724 to as high as 2.5 (Nelson and Sommers, 1996; Soil Survey Laboratory Methods
Manual, 1992). Broadbent (1953) recommended the use of 1.9 and 2.5 to convert
organic matter to total organic carbon for surface and subsurface soils, respectively.
The following steps should be performed for each subsample of matrix to be
analyzed. Note that several subsamples would normally be dealt with simultaneously
during this procedure.
1. Clean and dry crucible.
2. Weigh the labeled crucible to 0.0001 g. Since a label written on the crucible in
ink will not survive ignition, the crucible should be permanently and uniquely
marked by inscribing or etching a number or symbol on its side.
3. Weight �1 g of the clean sample into crucible and dry the crucible and its
content in the oven at 90 �C for 24 h.
4. Remove the crucible from the oven, place it immediately in the desiccator, put
the lid on the desiccator and allow the crucible and its contents to cool to room
temperature. When they are cool, remove the crucible and its contents to
weigh immediately to 0.0001 g. The crucible and its contents should be
exposed to the air for as short a time as possible to minimize increases in mass
as the sample equilibrates with laboratory humidity.
5. Allow the furnace to reach a temperature of 440 �C. Using the tongs, place the
crucible and its contents in the furnace for 24 hour.
6. Using the tongs, remove crucible and its contents fro the furnace and place
them immediately in desiccator to cool to room temperature.
� 39
7. When the crucible and its contents have cooled to room temperature, remove
them from desiccator and weigh immediately to 0.0001 g.
8. Calculate percentage of mass lost on ignition in the ground subsample.
9. Convert percentage of mass lost on ignition to percentage of total organic
carbon.
2.7 Minerals composition analysis
2.7.1 Minerals composition of coarse fraction
Concentration of heavy minerals and light minerals are performed by means of
high-density liquids. There is a considerable difference in densities between the
framework constituents and heavy accessory minerals of sediment. Upon immersion
of a sample in a liquid of an intermediate density ‘sink’ and ‘float’ fraction are
produced. There are called heavy and light fractions respectively (Mange and
Maurer, 1992). The ways of technique used will also have an effect on the quality of
the results obtained. Rittenhouse and Bertholf (1942) compare the effectiveness of
gravity settling and centrifuge separation. They observed that the weight percentage
of heavy mineral concentrate obtained by the two methods differ significantly, but the
number of the individual heavy minerals are the same in both methods. Recently,
Schnitzer (1983) presented results of his laboratory experiment. He found high
fluctuations in heavy mineral percentage from samples simultaneously, using
different liquids or different techniques. Variations also occurred when different
settling times or differ densities of bromoform were used. However, Schnitzer’s work
underline the importance of considering the possible influence of separation technique
on heavy mineral data. High density (highly toxic) liquids normally used for
separation are:
Density at 20 �C
Bromoform (tribromoethane) 2.89
� 40
Tetrabromoethane (acetylene tetrabromide) 2.96
Methylene iodide (di-iodomethane) 3.32
Clerici’s solution 4.24
Washing liquids suitable for removing the heavy liquids from the grain are:
carbon tetrachloride, benzene, alcohol (ethyl alcohol or methylated spirite) and
acetone. Because of their low toxicity, alcohol and acetone are frequently used.
In geological laboratories two basic technique are employed for standard
heavy liquid fractionation: (a) gravity settling or funnel separation, and (b) centrifuge
separation. The latter is the best for separation both of very fine (<63 �m) and of
sand-size sediments. This technique was already advocated in the mid-1920s, but
workers consistently encountered difficultly in achieving complete and
uncontaminated recovery of the two separates from the centrifuge tube.
In this study, gravity settling separation technique and bromoform
(tribromoethane) solution are used for separate heavy fractions out of light fractions
in sediment samples. Samples would normally be dealt during this procedure.
1. Requirment particle size after sieving that 1 � below mode.
2. Set equipment used for separation by gravity settling (Figure 2.12).
3. The heavy liquid (bromoform) is filled in the separating funnel.
4. Dry and weighed sample is added to the liquid.
5. Stir to ensure that the grains are wetted.
6. Waiting for grains sink (after 6-8 hours separating time).
7. Open the pinch clip slowly.
8. After heavy fraction is poured onto the filter paper in the lower funnel, close
pinch clip immediately.
9. Heavy fraction and light fraction are washed with acetone and set aside to dry.
10. Weigh dried heavy and light fraction sediments and label.
11. Heavy fraction to be mounted on the microscope slide.
12. Slide mount of heavy fraction will be determined in optical analysis.
13. Light fraction to be determined by binocular microscope.
� 41
Figure 2.12 Arrangement of equipments for heavy mineral separation by gravity
settling.
2.7.2 Minerals composition of fine fraction
X-ray diffraction method is the most widely used method for identification of
clay minerals and their crystalline characteristics. X-ray diffractogram was generated
using a Bruker x-ray diffractometer, model D8 Advance, at Department of Geological
Sciences, Faculty of Science, Chiang Mai University.
� 42
X-ray diffraction analysis was carried out by a CuK� generated at 18
kilowatts, 40 kilovolts and 30 milliamperes. For fine fraction clay, 2-theta start at 2�,
stop at 70�, steps 0.04�. Semi-quantitative estimation was determined. The highest
intensity of d-spacing refraction obtained from each mineral was selected to represent
the proportion of the mineral in the sample. The estimation was based on the
composition of the half peak area calculated from the height of the peak multiplied by
the half width at the midpoint of the peak height. This method of calculating the half
peak areas overcomes problems associated with inclined base lines and overlapping
peaks. The calculated half peak areas of all minerals in a sample were summed and
recalculated to 100 percent (Figure 2.13). Each mineral was calculated and the results
presented as a percentage value that could be either an underestimate or an
overestimate of the true proportion present. Thus, the most effective comparisons can
be made only between samples containing similar constituents.
Twenty-six representative samples from 5 stratigraphic sections in study area
were determined to mineral composition. These samples were selected from
interesting sediment layers. The minerals determined by this method indicate some
aspects of depositional environment.
2.8 Carbon-14 dating
Age of sedimentary deposit is importance for stratigraphic correlation with
another area. Geochemical isotope analyses are carried out to determine carbon
element. It constraints on the age of sediment are provided by 14C dating. This
method is based on the amount of 14C that has been absorbed by plants though
photosynthesis and also by absorbtion though roots. The values of 14C in individual
living organisms are uniform. When organisms die, 14C starts to decay radioactively a
stable rate. Then, its activity in dead plant tissues may be employed in order to
calculate the times, which has elapsed since they died. It is also assumed that the
sample which is to be dated has not been contaminated by modern 14C and that the
� 43
Figure 2.13 The calculated half peak area of every mineral found in a sample, was
summed and recalculated to 100 percent (after Ratanasthien, 1975).
observed activity is unaffected by any radioactive impurities in it (Attendorn and
Bowen, 1997).
The rate of decay of an unstable nuclide is proportional to the number of
atoms (N) remaining at any time (t). Translating the rate into mathematic language
results in below equation.
where = Rate of change of the number of present atoms. The minus sign
is required because the rate decreases as a function of time.
� 44
= Decay constant, specific of each element.
= Number of atoms.
The rate of decay of an unstable nuclide is measured by means of ionization
chambers (Faul, 1954; Smales and Wager, 1960). The operation of radiation
detectors reveals the presence of background radiation caused by natural and
anthropogenic environmental radioactivity. The rate of decay is measured in units of
becquerels and curies.
When radionuclide decays in a close system, a number of stable radiogenic
daughters (D*) that accumulate in a unit weight of rock or mineral. Over a long
period of time, the number of daughter atoms approaches the number of parent atoms
present initially. The interpretation of dating depends on certain assumptions about
the geological history (Faure and Mensing, 2005) as follows.
1. The rock or mineral sample being dated has not gained or lost parent or
daughter atoms except by decay of the parent to the stable daughter.
2. The decay constant of the parent nuclide is in dependent of time and is not
affected by the physical condition to which the nuclide may have been
subjected and its value is known accurately.
3. An appropriate value of Do is used in the calculation based on either
knowledge of the chemical properties of the daughter element or its isotope
composition in the terrestrial reservoir from which the rock or mineral
originated.
4. The measured value of D and N are accurate and representative of rock or
minerals being dated.
The concentration of the parent and daughter elements to be dated can be
determined by several methods. The choice depends on concentration of the element,
the amount of sample, lower limit of detection and availability of the required
instrumentation. Isotope dilution is generally agreed to be the supreme analytical
method for very accurate concentration determinations. A half-life for the
� 45
radioisotope of 5730±40a was gave by Godwin (1962) and indeed restated in 1982. A
previous and less accurate value of 5568±30a is still in use today.
De Vries (1958) demonstrated that the radiocarbon content of the atmosphere
varies in a systematic manner in the past, and also that the 14C activity around AD
1700 and 1500 was as much as 2% more than in the 19th-century. Another effect was
note by Suess (1995). He found that the activity of 20th-century wood is about 2%
lower than that of wood from the 19th-century and attributed this to the introduction of
dead CO2 into the atmosphere through the combustion of fossil fuel. This effect has
been exceeded since 1945 because the explosion of thermonuclear devices and
operating of nuclear reactors. They are artificial produce radiocarbon.
Carbon-14 age dating were generated using CAIS 0.5 MeV accelerator mass
spectrometer, at Center for Applied Isotope Studies, The University of Georgia,
United State of America. Sample would normally be dealt during this procedure.
1. The charcoal was given a standard chemical treatment similar the pretreatment
for cellulose described in Hedges et al. (1989) Archaeometry 31(2) 99-114.
2. The material was washed in ultrapure water.
3. Boiled in a sequence of mineral acids and bases (1M HCl/ 1 M NaOH/ 1M
HCl) to remove contaminating carbonate salts and humic acids.
4. The cleaned and treated material was then combusted at 900°C in evacuated
and sealed ampoules in the presence of CuO.
5. The resulting carbon dioxide was cryogenically purified from the other
reaction products and catalytically converted to graphite using the method of
Vogel et al. (1984).
6. Graphite 14C/13C ratios were measured using the CAIS 0.5 MeV accelerator
mass spectrometer.
7. The sample ratios were compared to the ratio measured from the Oxalic Acid I
(NBS SRM 4990).
8. The sample 13C/12C ratios were measured separately using a stable isotope
ratio mass spectrometer and expressed as �13C with respect to PDB, with an
error of less than 0.1%.