CHAPTER V Geochemistry - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/37106/8...5.3.1 X-Ray Fluorescence Spectrometry Collapsible aluminum cups were filled with 9 gm of boric

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CHAPTER V

Geochemistry

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5.1 INTRODUCTION

The chemical composition of a soil will be highly controlled by the composition of

the geological parent material, during the early pedogenesis, whereas the chemical

composition of mature soils strongly reflects the effects of weathering environment.

With time, soil composition diverges progressively from that of the parent material

under the influence of pedogenic processes determined by vegetation, topography

and, in particular, climate.

The divergence may be manifested initially by redistribution of elements within the

soil fabric, then between profile horizons and finally between soils within the

landscape (Jenkins and Jones, 1980).

The mobilization and redistribution of elements during weathering follow various

pathways as different elements are affected differently by the various pedogenic

processes including dissolution of primary minerals, formation of secondary minerals,

redox reactions, transport of material, and ion exchange (Middleburg et al., 1988).

There are several approaches to paleosols; it can be employed as litho-stratigraphic

markers or to define paleo-morphology. Paleosols provide an excellent reservoir of

information on weathering and climate conditions. For example compositions of

paleosols have been effectively used to estimate the PO2 of the atmosphere prevalent

at the time of their development (Holland and Zbinden 1988; Pinto and Holland 1988;

Zbinden et al., 1988; Holland et al., 1989; Holland and Beukes 1990; Holland 1994;

MacFarlane et al., 1994; Ohmoto 1996; Rye and Holland 1998).

The study of the Geochemistry of paleosols in the Precambrian sequences of India has

so far received very little attention. Some of the important literature on paleosols of

India is given here:

Dash et al (1987) demonstrated that the khondalites of Orissa probably represent

metamorphosed Precambrian aluminous lateritic soils. Similar high Al2O3 soils have

been reported as protoliths of the Precambrain sillimanite-corundum deposits of

Sonapahar of Meghalaya state, northeastern India (Golani 1989). The study by

Sharma, (1979) clarified some pyrophyllite-diaspore deposits of the Bundelkhand

Complex of Central India which have been interpreted as paleosols.

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In an attempt to chemically distinguish metamorphosed paleosols from metapelites of

the Precambrian of Peninsular India, Sreenivas and Srinivasan (1994) proposed that

khondalites, especially of the northern parts of the Eastern Ghats mobile belt may

represent metamorphosed Precambrian paleosols, whereas some high alumina rocks

of the Holenarasipur schist belt of the Dharwar Craton are metamorphosed

hydrothermal alteration products.

Apart from these, large deposits of fine grained micaceous rock at the base of the

Proterozoic Aravalli sequence (being mined as “Pyrophyllite”) have been interpreted

by Roy and Paliwal (1981) as possible paleosols. A major element geochemical study

by Banerjee (1996) has also suggested that these rocks may be Precambrian paleosols.

To understand their origin, much more detailed examination including trace and rare

earth element geochemical studies are essential. In this chapter, the chemical

composition of selected bed rock as well as weathered zones and top soil of seven

profiles of study areas have studied and discussed. Seven soil profiles that developed

on different bed rocks along with different horizons in the profile in the study areas

were analyzed for major and trace element.

The analytical data obtained from these rock samples and respected horizons are

presented in tables- 5.1 to 5.7.

Based on literature survey, not much work has been done on development of

paleosols in selected bed rocks in the study area and also mobility of elements along

the profile horizons. This study is an attempt to understanding the process of

weathering in Paleosols which developed on varieties of bed rocks that have been

identified and described in chapter 3.

5.2 SAMPLING

Based on different depths and horizons of the soil profile, comprehensive sampling

technique for chemical analysis was adopted. The sample patterns covering all the

facies consisted of sample sections in the vertical lithosection as well as weathered

and soils so as to give vertical as well as lateral variation of elemental distribution

patterns. A total of 35 samples were analyzed, of which 5 samples from Amphibolite

and 7 samples from Gneiss in Chikkahali area, 5 samples from Quartzo -feldspathic

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rock in Belagula area, 5 samples from calc-silicate rocks in Bettadabidu area, 3

samples from Amphibolite in Sargur area, Nugu dam, 4 samples from Hornblende

gneiss in Gundlupet area and 6 samples from Ultramafic rock in Doddakanya area.

5.3 ANALYTICAL PROCEDURE

The major and trace elements were analyzed by XRF (Philips, Holand) respectively at

CESS, Thiruvananthapuram.

5.3.1 X-Ray Fluorescence Spectrometry

Collapsible aluminum cups were filled with 9 gm of boric acid, which acts as binding

material. 1 gm of ~ 200 mesh homogenized sample powder was sprayed upon it by

covering the boric acid uniformly and about 15 tons of pressure was applied using

Herzog hydraulic press (H/100) to obtained pressed pellet of 40 mm diameter. The

pressed powder pellets allows trace element determinations, with limits of detection

up to 1 ppm for selected elements. The elements like K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu,

Zn, Rb, Sr, Zr, Co, Ba, Ce, Pb, La and P were determined with same method. Light

elements like Si, Al, Mg and Na are less precise by this method. All major and trace

elements are determined on sample pellets for which fused glass disk cannot be made

(for e.g. river and marine sediments, soils etc.).

Fused glass disk is prepared on a Claisse Fluxy instrument in the sample preparation

lab of CESS. One gram of finely powdered sample is mixed with 5 gram of flux

(LiT/LiM/LiBR 49.75/49.75/0.50, Pure) and fused in a platinum crucible. The fluxer

is microprocessor controlled and uses LPG and in controlled manner raises the

temperature up to 1000°C. It has built in programmes for different sample types.

Rotating and stirring of crucible for uniform mixing and pouring the fused liquid on to

a platinum mold to produce 30 mm glass disk is done automatically. It is also possible

to create need based programmes with different gas flow, crucible tilt, mixing speed

and length of each step.

Fused disks are excellent for analyzing major elements as it reduces matrix effects;

eliminates particle size effects; and provides a homogeneous specimen. Samples

which contain higher than normal concentrations of elements like lead, tin, arsenic

and/or antimony (as they can seriously damage the platinum ware) and samples which

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contain organic matter are not suitable for this method of sample preparation.

Elements determined by this method are Na, Mg, Al, Si, P, K, Ca, Ti, Mn, and Fe.

The samples were analyzed for major elemental composition by Philips Pw 1400

microprocessor controlled wavelength dispersive sequential X-Ray Fluorescence

spectrometer. The system was interfaced to a Philips P851 online minicomputer for

preparing calibration curve relating the concentration and intensity level in a

standards as well as unknown samples after due matrix corrections.

Software available in the computer was able to take care of dead time; background

and line overlap correction after regression and converting the counts into correction

with the help of the calibration curves, finally giving the output directly as

concentration in oxide percentage or in ppm as required. A spinner was used to spin

the samples inside the spectrometer while measuring to have uniform counts. Certain

elements were analyzed using a Rhodium target X-ray tube, while a Chromium X- ray

target tube estimated Na, Al and Mg, since the concentration levels of these elements

were very low. All the elements were estimated under a high vacuum condition (10-6

Torr). The major and minor elemental data estimated by XRF are reproducible with a

precision range of ± 5%.

5.4 Patterns of Element Concentration ( Depth–wise variation of elements)

The major, minor and the trace element abundances in all the seven representative

Paleosol profiles are analyzed and data has been presented in Tables- 5.1 to 5.7.

Major, minor element concentrations are given in weight percent as oxides and trace

elements in parts per million.

Variations of elements within the profile as a function of depth and a comparison of

mobile and immobile elemental concentrations (major and trace element) are made

for the parent and pedogenic horizons of the Paleosols profiles of the study areas

(Figures- 5.1 to 5.4).

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5.4.1 Major elements

a) Alumina (Al2O3)

The Al2O3 content of the profile developed on amphibolite ranges from 10.33% in the

parent rock to 15.34% in paleosols zone. Its content in profile developed on gneiss

ranges from 14.7 in bed rock to 17.13% in top soil horizon. In paleosol developed on

quartzo-feldespatic rock the Al2O3 content was 18.95% whereas in the lower

unaltered horizon was 10.76%. calc-silicate rock profile, the range of Aluminum

oxide content in less altered zone was 4.9% and 10.77% in soil zone. In the soil

profile developed on amphibolite in Sargur area, Al2O3 content are ranges from 5.24%

in upper portion of profile to 11.18 in bed rock. In soil profile developed on

hornblende gneiss, Al2O3 content gradually increased toward the soil horizon due to

slow alteration and its content correlates well with the proportion of the various

aluminum bearing minerals. Paleosol developed on rock of Doddakanya area also

shows very clear result with the gradual increase in alumina in the different separated

zones from the bed rock zone to soil horizon in top of the profile tables- 5.1 to 5.7.

Al2O3 is commonly assumed to be retained in the soil during weathering because Al

compounds are relatively insoluble under normal pH conditions and much of the Al is

incorporated in clay minerals (Birkeland, 1974). The study conducted by

Balasubramaniam (1978), demonstrated that, only under very low pH aluminum is

more soluble, but between pH 4 and 3 it is virtually insoluble and when the acidic

solution is naturalized alumina remains in solution.

Therefore the concentration of Al generally increases in the profile relative to the

parent rock during weathering since it is retained in the soil, while other components

are removed by leaching. This is generally the scenario in all paleosol profiles in the

current studies in and around Mysore (Figureures- 5.1 to 5.4). Mineral gibbsite is a

main carrier of alumina followed by kaolinite, allophone, diaspore and hydrous mica

in that order of sequence (Govinda M. S et al., 1997).

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b) Silica (SiO2)

Silica is one of the distinctive major elements in chemical features. The silica content

of the amphibolite profile in Chikkahali area varies from 50.3% in the parent material

to 53.9% in soil horizon, similar result also observed in profile developed on

amphibolite in Sargur area whereas the SiO2 content was varied from 55.16% in bed

rock to 63.69% in top soil (tables- 5.1- 5.7). In the profile developed on gneiss, the

silica content decreased from bed rock toward the paleosol horizon, which indicates

that it is slowly leaching out as result of chemical weathering on the other hand clay

formation is reflected in the decreased SiO2 and increased Al2O3 toward the surface.

Generally the bulk silica content in the zones above the altered basement rock is

represented by kaolinite and quartz. Compared to all the study profiles the soil profile

developed on ultramafic rock in Doddakanya area shows the less concentration of

silica in the parent materials as well as developed soil. The variations of silica in

entire profile in the study area are shown in Figures- 5.1 to 5.4).

c) Iron (Fe2O3)

The iron content discussed here is expressed as Fe2O3. Basically the soils developed

in humid condition in tropical and subtropical environments are more thoroughly

leached and possess Fe-rich in B horizon. There is a wide variation in the iron content

of the profile of studies area (tables- 5.1 to 5.7). The minimum, content of Fe2O3

(0.121 %) is recorded in unaltered hornblende gneiss of Gundlupet area and

maximum (27.58 %) is in the completely weathered amphibolite in Sargur area

(Figures- 5.1 to 5.4). This data shows the enrichment of iron oxide in the top most and

completely weathered zone of the paleosols profiles in the study region. There is a

gradual increase in the content of Fe2O3 from fresh rocks to slightly weathered and

completely weathered zone of the profiles.

d) Titanium (TiO2)

The low content of titanium is yet another important chemical feature of the paleosols

of the study areas. The total TiO2 content of the fresh parent amphibolite in

Chikkahali area is 0.43% and gradually increase in this amount is observed in top soil

around 0.8%. The gradual increase of TiO2 content in the upper zone of the profile

tabulated in tables- 5.1 to 5.7. The minimum content (0.26%) of TiO2 have been

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recorded in the fresh calc-silicate rock and maximum (1.14%) have been reported

from completely weathered zone of the profile developed on ultramafic rock in

Doddakanya region tables- 5.1-5.7 and Figures- 5.1 to 5.4.

The enrichment of titanium in the top soil is probably due to the presence of

crystallized or dispersed submicroscopic anatase which formed during the process of

weathering. Titanium precipitated normally at ˃ pH 2.5 and to be retained in a soil

profile because Ti compounds are also relatively immobile during weathering

(Sposito, 1989). Between the pH 4 and 5 elements like Ti, Al and Fe may become

relatively enriched by precipitation from solution (Loughman, 1969).

e) Loss On Ignition (LOI)

Results of loss on ignition (LOI) tests on samples from different depths are shown in

Tables- 5.1 to 5.7. The LOI test generally measures the molecular water content in

soil minerals (Nishida, 1999). Since most water is contained in the crystal structure of

clay minerals rather than in the rock minerals. The LOI value increased with

increasing degree of weathering probably due to the presence of hydroxide minerals.

5.4.2 Minor Elements

The details of each of the minor elements present in the profile are discussed below

and data expressed as percentage and showed in tables- 5.1 to 5.7.

a) Sodium (Na2O)

Sodium forms a soluble salt during weathering and is removed by circulating rain

water/meteoritic water. The content of soda in the entire profile range from 0.17% in

unaltered amphibolite and 0.25% in completely weathered zone respectively. In the

profile developed on gneiss the range was 3.73% in unaltered to 4.36% in highly

weathered respectively, but depleted in top soil due to influenced of the rain water. In

the quartzofeldspathic rock the sodium content was only 0.062% and strongly leached

toward the upper zones (1.04%) (Tables- 5.1 to 5.7 and Figures- 5.1 to 5.4).

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b) Potash (K2O)

Less amount of K2O are detected in all studies profile and like soda, k2O also strongly

depleted in paleosols horizons (tables- 5.1 to 5.7). The K-feldspar is the major mineral

containing substantial potash in the basement rock (granitic gneiss and also partly

from mica). During the hydrolysis, potassium is released from the mineral and forms

soluble salt and subsequently leached out.

c) Magnesia (MgO)

Magnesia almost depleted in all the zones of the profile toward the upper horizons,

MgO shows a gradual decrease in content from the parent rock to paleosols zone

(tables- 5.1 to 5.7), and shows less mobility during the weathering process. In the

profile developed on ultramafic rocks in magnesite mine in Doddakanya region,

unaltered parent material contains almost 32% magnesium whereas the top soil

exhibit only 10.9% and depletion being 3 times in the horizon. The variation of

percentage of MgO in paleosols profiles of the current study are shown in Figures- 5.1

to 5.4.

d) Limo (CaO)

The profile developed on calc-silicate rock shows high lime content (19.1%) in parent

material due to existence of calcite minerals and depleted through the profile horizons

(11% in top soil). The CaO also shows strong depletion in all the zones of the studies

profiles (tables- 5.1 to 5.7 and Figures- 5.1 to 5.4). In the early stage of weathering

calcium easily goes into solution than any other minor elements. In acidic condition

the calcite mineral converted to calcium bicarbonate and leached out and can enter in

to the underground water.

5.4.3 Trace Element

During the pedogenesis several geochemical process like selective mobilization,

leaching and partial precipitation of elements are involved in the weathering profile.

The behavior of trace elements during the weathering has been discussed by several

researchers (Gardon and Murata, 1952; Adams and Richardson, 1960; Chowdry et al.,

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1965; Balasubramanian and Srikant, 1984; Khandali and Devaraju, 1986; Krishna

Rao et al., 1987).

The role of trace elements is usually linked with major elements, but in the case of

residual deposit such a linkage is untenable (Balasubramanian and Srikant, 1984).

Therefore, the geochemical behavior of individual trace element during the process of

weathering is considered.

a) Vanadium (V)

The paleosols are a potential source of vanadium as a by-product of weathering. There

is a gradual increase in the concentration of V from the parent rock toward the upper

horizons in the almost studies profile (Tables- 5.1 to 5.7 and Figures- 5.1 to 5.4). The

maximum content of vanadium is recorded from top soil developed on ultramafic rock

in Doddakanya area (204 ppm), followed by paleosols developed on amphibolite

profile in Chikkahali region (154 ppm). Vanadium probably occurs in magnetite,

biotite, hornblends and Ti- minerals of fresh bed rock.

Vanadium is closer related to ferric iron than aluminum (Goldschmidt, 1954). During

the process of weathering the precipitation of soluble vanadate is aided by hydroxides

of ferric iron, Therefore the concentration of V is always more in the rich iron soils.

b) Chromium (Cr)

In the process of weathering, chromium presented in pyroxene and probably

amphibolite and biotite might have released in solution. Whereas, Cr which is

presented in the structure of magnetite and limonite gets concentrated mechanically as

these minerals are resistances to chemical weathering (Rankama and Shama, 1950).

The high concentration of Cr can also occur in Kaolinite (Mclaughlin, 1959), which is

very similar to those of Al+3

and Fe+2

. Therefore, it can have an isomorphous

substitution in aluminous and ferric iron minerals.

The highest content of Cr is recorded in the parent rock horizon of the profiles

developed on ultramafic rock (5467 ppm), followed by the in unaltered amphibolite in

Chikkahali area (2698 ppm) (Tables- 5.1 to 5.7). The variations of Cr in the studied

profiles are shown in Figures- 5.1 to 5.4.

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c) Nickel (Ni)

Most of the nickel in the parent rock is represented by the ferromagnesian minerals as

well as ferric hydroxide minerals. High concentration of Ni is recorded from the

highly weathered zones of profile developed on ultramafic rock in magnesite mine

(2751 ppm), probably related to rather high iron oxide minerals present in the area

(Tables- 5.1 to 5.7). The concentration of Ni in the paleosols profiles depend on the

degree of alteration, on the other hand in highly or completely weathered horizon the

concentration of the Ni is high (Figures- 5.1 to 5.4).

d) Cobalt (Co)

Cobalt is incorporated in the ferromagnesian minerals of parent rocks (Carr and

Tunekian, 1961). Such minerals of parent rock (gneiss, hornblende gneiss,

quartzofeldspathic …) under the condition of chemical weathering are converted to

goethite and limonite, which are likely to contain Co in different lithounits of the

profile.

The maximum Co content is recorded in the hornblende gneiss profile (32 ppm) and

the minimum in the calc-silicate rock (9 ppm) see tables- 5.1 to 5.7. There is not much

variation in the concentration of Co in the profile horizons (Figures- 5.1 to 5.4).

e) Copper (Cu)

The copper contents of parent rocks in different paleosols profiles in the study areas

were varied from 12 ppm to 62 ppm. The maximum content of cupper was recorded

in amphibolite followed by ultramafic rock and minimum was observed in quartzo-

feldspathic rock in the profile examined from Belagula region (Tables- 5.1 to 5.7).

Moderate variation was observed through the profiles especially in weathered

horizons (Figures- 5.1 to 5.4).

Based on the ionic potential of cu, it is expected to pass into ionic solution and

thereby get depleted during the process of weathering (Rao and Murthy, 1981). The

study conducted by Rankama and Shama (1950), demonstrated that the higher

concentration of Cu in highly weathered zones may be due to the highest iron content

as cu replace ferrous iron due to their similarity in ionic radii.

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f) Zinc (Zn)

Zn is usually present in the ferromagnesian minerals. The geochemistry Zn is similar

to magnesium iron group of metals due to their large ionic radii, especially between

zinc and iron (Goldschmidt, 1954). Less variation of Zn content have observed in the

profiles might be due to the slow rate of weathering. High Zn contents have recorded

in highly weathered horizons can be related to the presence of higher contents of iron

minerals (Rao and Murty, 1981). High concentration of Zn has been recorded from

weathered amphibolite in Sargur region (Tables- 5.1 to 5.7). The depth wise variation

diagram of Zn in the studied profiles is also shown in the variation diagram Figures-

5.1 to 5.4.

g) Rubidium (Rb)

The variations of Rb in the studied profiles were low to moderate, high concentration

of Rb clearly recorded from weathered zones followed by top soils. Among the all

studied profile, weathered ultramafic rock in Doddakanya area shows high Rb content

(Tables- 5.1 to 5.7 and Figures- 5.1 to 5.4). The chemical behavior of alkali Rb is very

similar to that of potassium. During the chemical weathering, Rb and other alkali

metals are also brought into solution and subsequently removed and precipitated or

absorbed by the clay due to their small ionic potential (Rankama and Sahama, 1950).

h) Strontium (Sr)

The high content of Sr in bed rock of the study areas is belong to Amphibolite (388

ppm), followed by gneiss (313 ppm) then calc-silicate (54 ppm) and finally

hornblende gneiss (27 ppm). Slow to moderate depletion through the upper horizons

of the mentioned profiles is reported (Tables- 5.1 to 5.7 and Figures- 5.1 to 5.4).

Generally, the mineral plagioclase contains as appreciable amount of Sr (Rankama

and Sahama, 1950) and the geochemical behavior of Sr in weathering process is

similar to that of calcium. It rapidly enters into an aluminous solution and removed by

circulating water.

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Table- 5.1: Major (in oxide weight percent) and Trace (in ppm) elements abundances

in the profile developed on amphibolite in Chikkahali area.

T: Trace

ND: Not detected / below detection limit

C: bed rock, B1: moderately weathered, B2: highly weathered, B3: completely weathered

Sample C B1 B2 B3 Soil

SiO2

50.351

56.125

52.081

51.785

53.949

Al2O3 10.333 8.412 9.403 9.799 15.347

TiO2 0.437 0.396 0.411 0.441 0.789

MnO 0.135 0.177 0.106 0.124 0.158

Fe2O3 11.162 10.145 9.729 9.935 11.678

CaO 5.922 3.339 3.675 2.823 2.435

MgO 16.965 17.305 14.984 14.394 5.494

Na2O 0.174 0.202 0.133 0.118 0.258

K2O 0.008 0.055 0.026 0.083 0.561

P2O5 0.049 0.033 0.035 0.032 0.055

LOI 4.100 3.400 9.100 10.100 9.000

Total 99.636 99.589 99.683 99.634 99.724

Trace elements (in ppm)

V 136 109 100 104 152

Cr 2506 2698 2107 2432 1269

Co 24 24 22 23 23

Ni 666 932 657 728 388

Cu 65 30 8 47 64

Zn 82 75 72 75 78

Rb 35 35 74 64 67

Sr 22 14 20 18 59

Zr ND ND ND ND 266

Ba 20 114 28 74 256

La 17 22 16 21 28

Ce 35 35 34 38 72

Pb 19 19 26 24 21

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in the profile developed on gneiss in Chikkahali area.

Sample C B1 B2 B3 B4 B5 Soil

SiO2 72.002 68.906 69.865 69.934 69.932 72.842 65.692

Al2O3 14.726 14.077 15.757 16.595 15.228 16.184 17.133

TiO2 0.427 0.587 0.411 0.355 0.474 0.395 0.791

MnO 0.023 0.066 0.012 0.014 0.026 0.013 0.057

Fe2O3 0.548 4.492 0.670 0.659 1.453 0.624 4.521

CaO 0.644 2.889 1.721 1.145 0.545 1.044 1.911

MgO 0.770 2.330 1.165 1.013 0.884 0.690 1.677

Na2O 3.734 3.053 4.436 4.366 3.446 3.311 2.263

K2O 3.386 2.304 2.252 2.696 2.785 3.213 2.716

P2O5 0.078 0.113 0.084 0.077 0.079 0.032 0.057

LOI 3.500 1.050 3.500 3.000 5.000 1.500 3.000

Total 99.838 99.867 99.873 99.854 99.852 99.848 99.818


V 59 94 55 54 69 56 90

Cr 31 71 29 27 34 20 61

Co 10 14 11 10 11 10 14

Ni 36 47 44 35 33 24 52

Cu 12 30 21 4 13 21 31

Zn 56 79 55 54 53 48 85

Rb 135 151 128 109 143 118 146

Sr 313 275 357 379 163 254 196

Zr 269 139 195 306 148 258 395

Ba 501 283 234 348 618 580 478

La 46 36 23 26 34 32 96

Ce 119 87 76 71 110 63 132

Pb 23 26 29 23 28 27 29

T: Trace


C: bed rock, B1: moderately weathered, B2, B3: highly weathered, B4, B5: completely weathered

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in the paleosols developed on quartzo-feldspathic rock in Belagula area.


SiO2 57.174 48.193 51.650 53.587 67.546

Al2O3 18.955 9.365 9.271 8.823 10.764

TiO2 0.925 0.945 0.867 0.752 0.584

MnO 0.086 0.163 0.135 0.094 0.065

Fe2O3 7.151 14.698 13.942 13.493 7.206

CaO 1.691 7.609 7.193 4.616 2.673

MgO 1.700 14.963 12.922 12.527 5.367

Na2O 0.062 1.266 0.829 0.557 1.043

K2O 0.365 0.402 0.279 0.264 1.852

P2O5 0.116 0.160 0.120 0.053 0.049

LOI 11.600 1.850 2.400 4.850 2.600

Total 99.825 99.614 99.608 99.616 99.749


V 159 196 186 150 104

Cr 533 2003 2177 2238 1226

Co 18 29 27 26 18

Ni 159 1069 1069 1008 497

Cu 43 89 54 73 43

Zn 82 87 83 78 66

Rb 85 34 12 43 75

Sr 16 117 118 61 106

Zr 277 18 30 ND 63

Ba 195 115 78 73 214

La 41 21 20 23 21

Ce 89 41 44 44 34

Pb 28 18 15 20 20

T: Trace



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in the profile developed on calc-silicate rock in Bettadabidu area.


SiO2 58.705 92.502 13.946 54.649 44.645

Al2O3 4.907 5.125 6.102 6.345 9.777

TiO2 0.262 0.267 0.322 0.318 0.595

MnO 0.384 0.082 0.590 0.665 1.768

Fe2O3 1.414 T 2.445 4.630 12.592

CaO 19.104 0.353 47.954 19.014 11.063

MgO 8.883 0.465 12.105 10.342 8.400

Na2O 0.031 T 0.044 0.057 0.063

K2O T T 0.503 0.132 0.483

P2O5 0.031 0.025 0.053 0.060 0.087

LOI 6.250 1.150 15.900 3.750 10.500

Total 99.971 99.969 99.964 99.962 99.973


V 37 41 49 55 101

Cr ND 16 19 30 132

Co 10 9 11 13 19

Ni 11 22 25 39 59

Cu 9 3 5 3 27

Zn 57 42 49 71 66

Rb 19 64 46 25 34

Sr 54 2 41 19 19

Zr ND ND ND ND 26

Ba 14 18 36 23 190

La 13 19 15 18 27

Ce 34 34 38 41 48

Pb 16 25 19 17 17

T: Trace



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in the profile developed on amphibolite in Sargur area.

Sample C B1 Soil

SiO2 55.167 63.501 63.698

Al2O3 11.188 5.104 5.246

TiO2 0.687 0.272 0.278

MnO 0.127 0.023 0.034

Fe2O3 21.419 22.893 27.588

CaO 4.593 5.278 1.151

MgO 2.577 1.167 0.808

Na2O 0.556 T T

K2O 0.263 T T

P2O5 0.099 0.087 0.119

LOI 3.250 1.650 1.050

Total 99.926 99.975 99.972


V 167 47 53

Cr 134 31 18

Co 29 28 32

Ni 71 18 13

Cu 62 ND ND

Zn 69 51 53

Rb 12 ND ND

Sr 27 4 2

Zr ND ND ND

Ba 74 11 19

La 23 17 18

Ce 40 34 34

Pb 14

11

11

T: Trace


C: bed rock, B1: completely weathered

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Table- 5.6: Major (in oxide weight percent) and Trace (in ppm) elements

abundances in the profile developed on hornblende gneiss in Gundlupet area.

Sample C B1 B2 Soil

SiO2 75.181 46.619 51.876 69.358

Al2O3 13.824 17.769 13.391 17.544

TiO2 0.328 1.329 1.175 0.534

MnO 0.019 0.218 0.154 0.046

Fe2O3 0.121 17.306 14.140 3.158

CaO 1.189 7.301 8.708 1.375

MgO 0.321 2.484 2.619 1.077

Na2O 4.026 0.732 1.652 1.927

K2O 3.025 0.519 0.489 1.797

P2O5 0.038 0.110 0.207 0.059

LOI 1.800 5.500 5.500 3.000

Total 99.872 99.887 99.911 99.875


V 42 285 234 72

Cr 7 100 62 67

Co 10 28 24 13

Ni 16 79 43 45

Cu 22 101 93 25

Zn 57 132 105 66

Rb 122 19 24 122

Sr 388 62 97 258

Zr 112 22 43 186

Ba 398 193 88 260

La 20 25 20 22

Ce 43 56 38 55

Pb 23 15 16 29

T: Trace


C: bed rock, B1: moderately weathered, B2: completely weathered

180


in the profile developed on ultramafic rock in Doddakanya area.

Sample C B1 B2 B3 B4 Soil

SiO2 36.422 33.445 45.313 27.686 40.178 47.248

Al2O3 5.273 5.565 5.025 6.689 5.190 9.482

TiO2 0.292 0.283 0.268 0.321 0.274 1.148

MnO 0.120 0.108 0.120 0.037 0.103 0.162

Fe2O3 9.206 8.339 9.139 1.174 7.753 14.738

CaO 1.615 7.961 1.429 9.737 2.743 9.974

MgO 32.083 24.634 22.285 29.742 22.411 10.948

Na2O 0.128 0.114 0.072 0.092 0.085 1.378

K2O T T T T T 0.265

P2O5 0.034 0.033 0.036 0.026 0.032 0.130

LOI 14.000 18.800 15.600 24.200 20.600 4.250

Total 99.173 99.282 99.287 99.704 99.369 99.723


V 53 59 48 49 52 204

Cr 5467 4697 3543 1417 4435 1518

Co 27 25 27 13 24 27

Ni 2492 2159 2751 1129 2052 528

Cu 10 10 ND 7 8 94

Zn 62 59 54 48 57 89

Rb 54 24 62 94 37 25

Sr 6 36 3 91 10 122

Zr ND ND ND ND ND 6

Ba 17 32 52 14 60 69

La 13 14 17 16 16 23

Ce 35 39 34 38 34 48

Pb 23 17 24 31 20 17

T: Trace


C: bed rock, B1: moderately weathered, B2: highly weathered, B3, B4: completely weathered

181

Figure- 5.1: Abundances and distribution of major, minor (in oxide weight %) and

trace element (in ppm) of Paleosols profiles; (A) developed on amphibolite and (B)

developed on gneiss in the Chikkahali area.

A

B

182


trace element (in ppm) of Paleosols profiles; (A) developed on quartzo-feldspathic

rock in Belagula area and (B) developed on Calc-silicate rock in the Bettadabidu area.

B

A

183


trace element (in ppm) of Paleosols profiles; (A) developed on amphibolite in the

Sargur region and (B) developed on hornblende gneiss in Gundlupet area.

B

A

184


trace element (in ppm) developed on ultramafic rock in Doddakanya region

(magnesite mine).

185

5.5 CHEMICAL VARIATIONS

Geochemical parameters can be used as paleo-climate indicators and for inferring the

weathering conditions. However, most of the elements can be variably mobile during

post-depositional and metamorphic events. The geochemical trends in mature paleosol

profiles reflect the weathering of minerals, gravitational processes of leaching and

translocation, and the capillary processes that produce calcification or salinization

(Gill and Yemane, 1996).

Leaching, transfer and dissolution of the major and trace elements during pedogenesis

is greatly controlled by chemical constituents of the country rock and the surface,

besides the prevailing climatic conditions (Nesbitt and Young, 1982, 1984, 1989;

Maynard, 1992; Mc Lennan et al. 1993; Soil Survey Staff, 1999). Therefore, relative

geochemical variations across a profile inclusive of parent, gives an insight into the

degree of pedogenesis and environmental conditions persisted during pedogenesis

(Retallack, 1995; Sheldon et al. 2002). On the other hand depletion of mobile and

enrichment of immobile components in the Parent material and their corresponding

paleosols are distinct features of any paleosol profiles (Nagendera G et al., 2009).

5.5.1 Concentration Ratio of Major, Minor and Trace Elements Related to

Al2O3 and TiO2

The Al and Ti are highly conserved in the almost soil profile, the nature of chemical

weathering can be determined by making concentration ratio (CR) diagrams based on

the assumption that Al and Ti are retained within the soil profile. Naturally, some Al

and Ti are moved during weathering, although their solubility and mobility is

relatively low (Gay and Grandstaff, 1980). To understand the enrichment and

depletion of major and trace elements in the studied paleosols developed on different

parent material the method described by Gay and Grandstaff (1980), have been used.

The equations used to obtain concentration ratio (CR) is:

( )

( )

And

186

( )

( )

Where, M weathered is the concentration of major and trace elements in the

weathered zone and M parent is the concentration major and trace elements in the

parent rock.

The method of Muhs et al., (1987) also has been used to estimate the depletion and

enrichment of SiO2 relative to immobile constituents R2O3= (Al2O3+Fe2O3+TiO2)

compared to the presumed parent rock, the following equation is used:

5.5.1.1 Profile 1 (Chikkahali area)

The profile developed on amphibolite as a parent material in Chikkahali area have

been subjected for the calculation of concentration ratio (CR) of major, minor and

trace elements through the profile. The relative changes in abundances of the major,

minor and trace elements in the above profiles relative to Al2O3 and TiO2 are shown

in Figure- 5.5 A and B.

SiO2 shows slight to moderate depletion at the upper horizon toward the top of the

profile relative to Al2O3 (Figure- 5.1 A). Relative to TiO2, SiO2 is very slightly

depleted evenly throughout the profile, with the exception of the lower portion of the

B horizon (Figure- 5.1B). Weight percent ratios of SiO2 to R2O3 (Al2O3+Fe2O3+TiO2)

in this profile is showing depletion of SiO2 relative to (Al2O3+Fe2O3+TiO2) in the

profile Figure- 5.12 A.

Sposito (1989) demonstrated that SiO2 is conserved in the soil profile under low to

moderate leaching conditions. SiO2 is usually retained in clay minerals under such

conditions (Gay and Grandstaff, 1980). However, under intense leaching conditions,

SiO2 is removed and depleted in top horizon (Sposito, 1989).

Fe2O3 shows less depletion in the middle of the profile, but Fe2O3 is moderately

depleted from the surface of the profile (Figure. 5.5 A and B). During weathering and

diagenesis the oxidation state of iron changes (Gay and Grandstaff, 1980). Diagenesis

187

usually changes the iron from ferric (Fe+3

) to ferrous (Fe+2

) state, with little changes in

the total Fe content (Veizer, 1973).

Changes in the iron content can however be used to show whether oxidation or

reduction has occurred during the process of weathering. If conditions are oxidizing

during soil formation, iron mobilized by dissolution of primary minerals is oxidized to

insoluble Fe+3

and precipitates in the soil profile as ferric iron oxide or hydroxide

minerals but under reducing conditions iron is reduced to the more soluble Fe+2

,

which may be removed by groundwater (Soil Survey Staff, 1975).

Figure- 5.5 illustrate that iron was lost from the A horizon. Therefore surface loss and

subsurface gain of iron in the profile suggests that during weathering, soil waters were

under oxidizing conditions. The colors mottling occurring in the profile suggests that

reduction (gleying) may have occurred in this profile due to iron oxidation state

variations. Diagenesis may have had an impact in causing color changes in the

paleosol profile.

The concentration ratio of TiO2 related to Al2O3 in the B horizon was slightly depleted

whereas in top soil very less enriched but in terms of Al2O3 related to TiO2 the result

was reverse.

The concentrations ratio of MgO, CaO, K2O, Na2O, P2O5, MnO, Ni, Zn, and Cr

related to Al2O3 and TiO2 decrease from the parent rock to the paleosol (Figure- 5.5 A

and B). The depletion of Na2O was high in B horizon but the degree of depletion

decreased in A horizon. Cupper ratio decreased in weathered horizon and in top soil

slightly enriched. Sr and Rb gradually enriched toward the paleosols and Ba element

concentration strongly depleted in weathered horizon then gradually enriched toward

the top soil.

5.5.1.2 Profile 2 (Chikkahali area)

The paleosol developed on gneiss in Chikkahali area have been tested for chemical

variation through the profile. The relative changes in abundances and variation of the

major, minor and trace elements in this profile, relative to Al2O3 and TiO2 are shown

in Figure- 5.6 A and B.

188

The concentration ratio of SiO2 related to Al2O3 didn’t change significantly but

weight-percent ratios of SiO2 related to R2O3 shows slightly depletion in surface of the

profile (Figure- 5.12 B). The CR value of Al2O3 related to TiO2 shows slight

enrichment in upper horizon but in top soil it had similar concentration with parent

material. Iron oxide concentration in the profile strongly depleted in less weathered

and highly weathered horizons but in the paleosols, degree of depletion significantly

decreased might be due to oxidation stage of iron.

Same as amphibolite profile in the same region the concentration ratio of MgO, CaO,

K2O, Na2O, P2O5, MnO, Ni, Zn, Rb, V, Cu, Sr and Cr related to Al2O3 and TiO2

decrease from the parent rock to the paleosol (Figure- 5.6 A and B). In modern soils,

most of these constituents are depleted from the profile (Sposito, 1989). This is the

case for the above said profile in Chikkahali region. Ba ratio related to Al2O3 shows

graduate enrichment towards the profiles but in relation with TiO2 the degree of

enrichment is strong.

5.5.1.3 Profile 3 (Belagula area)

The profile developed on quartzo-feldspathic rock in Belagula region was

geochemically analyzed and concentration ratio of major and trace elements related to

Al2O3 and TiO2 calculate. The Figure- 5.7 A and B shows the relative changes in

abundances and variation of the major, minor and trace elements in this profile.

The SiO2 concentration ratio was slightly enriched from parent material to top soil;

same result also came out when weight-percent ratios of SiO2 related to R2O3

calculated (Figure- 5.12 C). Iron oxide shows the graduate depletion toward the upper

horizons, in the case of Al2O3 related to TiO2 slightly enrichment has observed. The

concentration ratio of MgO, CaO, P2O5, MnO, Ni, Zn, Rb, V, Cu, Sr and Cr related to

Al2O3 and TiO2 decrease from the parent rock to the paleosol (Figure- 5.7 A and B).

CR value of Na2O was depleted in weathered zone the enriched in the paleosols. Ba

and K2O related to TiO2 shows gradual increasing in the Cr value through the profile.

5.5.1.4 Profile 4 (Bettadabidu area)

The chemical variations of paleosol developed on calc-silicate rock in betadabeddue

area have been examined. Soil profiles of arid and semi-arid climates often contain

189

pedogenic calcretes which can be used as an indicator for the maturity of paleosols.

The relative changes in abundances of the major and trace elements in the profile

relative to Al2O3 and TiO2 are shown in Figure- 5.8 A and B.

The concentration ratio of SiO2 related to Al2O3 and TiO2 shows moderate to slight

depletion in weathered and top soil respectively, weight-percent ratios of SiO2 related

to R2O3 also shows slight enrichment in A horizon (Figure-5.12 D). Fe2O3 is strongly

enriched from parent material to paleosols might be due to extreme environment

condition of earth in past. Precambrian paleosols on Earth clearly formed in a world

of running water and atmosphere, and may provide evidence of variation in their fluid

environment with time (Holland, 1984). Atmospheric oxygenis the main oxidizing

agent in the present atmosphere and its effect on weathering is profound. Iron

liberated by dissolution of minerals is oxidized to ferric oxides (Fe2O3 or Hematite),

hydroxides or oxyhydrates, in which iron is in the trivalent state (Fe3+

).

Under reducing conditions, iron released from minerals remains in its reduced state

(Fe2+

), within drab coloured silicates (such as chlorite), sulphides (pyrite) or

carbonates (siderite). Since bivalent iron is much more soluble than trivalent, iron

tends to be lost from soils formed under reducing conditions.the iron content and

colour of paleosols are potentially useful guides to the changing oxygen content of

past atmospheres.

The concentration ratio of MgO, CaO, Na2O, P2O5, MnO, Ni, Zn, Ba, V, Cu, Sr and

Cr related to Al2O3 and TiO2 increased from the parent rock to the paleosol (Figure-

5.8 A and B).

5.5.1.5 Profile 5 (Gundlupet area)

In the paleosols developed on hornblende gneiss, CR value of SiO2 slightly decreased

from parent rock to top soil (Figure- 5.12E). Same as calc-silicate profile the CR of

Al2O3 increased but the trend of increasing was moderate might be due the clay

formation which is reflected in the decreased SiO2 and increased Al2O3 toward the

surface (Figure- 5.9 A).

The concentration ratio of MgO, CaO, Ni and Cr related to Al2O3 and TiO2 decreased

from the parent rock to the paleosol whereas The concentration ratio of Na2O, P2O5,

190

MnO, Zn, Ba, V, Cu and Sr related to Al2O3 and TiO2 increased from the parent rock

to the paleosol (Figure- 5.9 A and B).

5.5.1.6 Profile 6 (Sargur area)

A paleosol developed on amphibolite in Sargur area was analyzed for variation of

major and trace elements in different horizons of the profile. The concentration ratio

of major and trace elements related to Al2O3 and TiO2 are shown in Figure- 5.10 A

and B.

Weight-percent ratios of SiO2 related to R2O3 are strongly to moderately decrease in

weathered zone to top soil respectively (Figure- 5.12 F). The concentration ratio of

major and trace elements such as of TiO2, MgO, CaO, P2O5, MnO, V, Cu, and Sr

related to Al2O3 decreased from the parent rock to the paleosol where as the CR value

of Na2O, K2O, Zr, Rb and Ba slightly increased in upper zones (Figure- 5.10 A and

B). Ni, Zn and Cr shows opposite result when calculated with TiO2. Ni related to TiO2

shows strong enrichment in surface compare with parent material. However, the

enrichment of this element is generally greatest in the lower half of the profile along

with clay and iron oxides (Figure- 5.10 B).

5.5.1.7 Profile 7 (Doddakanya area)

One profile of the paleosols developed on ultramafic rock in Doddakanya area has

been geochemically analyzed to check the variation of elements in the profile. The

concentration ratio of major and trace elements related to Al2O3 and TiO2 are shown

in the Figure- 5.11 A and B.

In this profile the weight-percent ratios of SiO2 related to R2O3 slightly depleted

(Figure- 5.12 G). TiO2 shows less enrichment towards the soil surface. Iron oxide

depleted in weathered zone and slight enrichment are observed in A horizon (Figure-

5.11 A and B)

The concentration ratio of major and trace elements such as of MgO, CaO, MnO, Rb,

Ni, and Zn related to Al2O3 decreased from the parent rock to the paleosol whereas

the CR value of Na2O, P2O5, Sr, Cu, V and Ba slightly increased in upper zones

(Figure- 5.11 A).

191

Figure- 5.5: Concentration ratio diagram for profile 1 (Paleosols developed on

amphibolite) showing enrichment and depletion of constituents of major and trace

elements; A) relative to Al2O3 B) relative to TiO2.

A

B

192


gneiss) showing enrichment and depletion of constituents of major and trace


A

B

193


quartzofeldspathic rock) showing enrichment and depletion of constituents of major

and trace elements; A) relative to Al2O3 B) relative to TiO2.

A

B

194

Figure- 5.8: Concentration ratio diagram for profile 4 (Paleosols developed on calc-

silicat rock) showing enrichment and depletion of constituents of major and trace


A

B

195


amphibolite) showing enrichment and depletion of constituents of major and trace


A

B

196


hornblende gneiss) showing enrichment and depletion of constituents of major and

trace elements; A) relative to Al2O3 B) relative to TiO2.

A

B

197


ultramafic rock) showing enrichment and depletion of constituents of major and trace


B

A

198

Figure- 5.12: Plots of weight-percent ratios of SiO2 to R2O3 in the all studied profiles

of the studied areas showing depletion and enrichment of SiO2 relative to immobile

constituents (Al2O3+Fe2O3+TiO2) compared to the presumed parent rock.

199

5.6 Intensity of Weathering Conditions (Molecular Weathering Ratios)

Molecular weathering ratios reveal changing chemical proportions and estimation of

various ratios of the mobile and immobile oxides as a result of processes or properties

like salinization (Na2O/ K2O), calcification ((CaO + MgO)/ Al2O3), clayeyness

(Al2O3/SiO2), Hydrolysis (Al2O3/(CaO + MgO + Na2O + K2O)), leaching (Ba/ Sr),

chemical index of alteration (CIA), chemical index of alteration (CIW) and

Weathering (Fe2O3/SiO2) based on description demonstrated by Nesbitt and Young,

(1982, 1984) and Sawyer, (1986).

These approaches have been widely used (Retallak 1983, 1991) because it is

relatively free from assumption except that the material in question is indeed a

paleosol and that changing molar proportions of elements are related to common

weathering reactions found in soils today.

5.6.1 Salinization

Based on the equation introduced by Retallack (2001), Salinization of the paleosols

profiles (i.e., accumulation of soluble salts during weathering) can be calculated using

the following equation:

The values less than 0.2 are below the salinization, whereas soils with values greater

than 2 have been affected by salinization (Retallack, 2001). There is no increase in the

ratio near the top of the paleosol profiles, which is also consistent with minimal to

moderate salinization in all studied profile. Almost in the entire profiles, weathered

zone more affected by salinization and top paleosols shows minimal salinization. The

variations of salinization ratio in all the studied profile are presented in Figure- 5.13,

Whereas A) is represented the profile developed on amphibolite profile, B) gneiss, C)

quartzo-feldspathic, D) calc-silicate and E) hornblende gneiss as parent rocks.

5.6.2 Clayeyness

The second molecular weathering ratio that was applied is "clayeyness". The relative

clayeyness suggests significant clay accumulation especially in the bottom portion of

200

the B horizon, where the ratio should increase due to clay production during

pedogenesis (e.g., Sheldon, 2006; Sheldon and Tabor, 2009).

The following equation widely used to estimate the rate of clay formation during the

pedogenesis:

The data obtained from this ratio shows clayeyness, parameters increases with higher

pedogenic levels in the almost all the profiles and only in the profiles developed on

calc-silicate rock and quartzo-feldspathic rock minimal decreasing trend are observed.

The clayeyness data calculated from the studied profiles of all studied profiles and the

variation in the profile are shown in Figure- 5.14. The profiles developed on

amphibolite (A), gneiss (B), quartzo-feldspathic (C), hornblende gneiss (F) and

ultramafic rocks shows slow clayeyness process whereas the profile developed on

calc-silicate rock shows moderate trend toward the upper horizon.

5.6.3 Calcification

The calcification parameter varies in complement with the abundance of calcretes

accumulation in the paleosol horizons. The calcification is an evident in the paleosol

profile. The calcification ratio can obtain by the following formula:

( )

The paleosols developed on calc-silicate (D), amphibolite (profile A, E) and

ultramafic rocks (G) decreasing with higher pedogenic levels while the profiles

developed on gneiss (B), quartzofeldspathic (C) and hornblende gneiss (F) rocks

shows low increases trend. The Figure- 5.15 shows the variation of calcification ratio

in the all seven studied profiles.

5.6.4 Hydrolysis (base loss)

Application of the hydrolysis ratio is based on the idea that as minerals are weathered,

base cations are lost relative to Al during clay formation. These values indicate the

removal of mobile cations by extreme leaching (Gill and Yemane, 1996).

201

Hydrolysis is calculated with the following equation (Retallack, 2001):

( )

The profiles developed on amphibolite (A and E) and ultramafic rocks (G) shows high

hydrolysis toward the upper horizon whereas the profiles developed on gneiss (B),

calc-silicate (D) and hornblende gneiss (F) shows moderate hydrolysis in paleosols

zone (Figure- 5.16). In the paleosols profile developed on quartzo-feldspathic rock

(C), the hydrolysis was decreased in top horizons. The degree of hydrolysis in the soil

profiles work as an indicator for high leaching activity during the pedogenesis.

Positive and negative peaks of the base loss, respectively indicates the relative

abundance of the bases and the refractive element (Al2O3). In the paleosols developed

in the study area, relative base loss is very strong (Figure- 5.16).

5.6.5 Leaching

One method of measuring the degree of chemical weathering (or leaching) in the soil

profile is obtained by observing molecular weathering ratios as given by Gill and

Yemane (1996). The degree of leaching may be assessed by considering the following

equation (Retallack, 2001):

All the seven profiles in the study area subjected for calculation of degree of leaching

based on different parent material. The solubility differences between the two

elements (Ba < Sr) gives rise to higher values in more leached samples. The profiles

developed on amphibolite (A and E), gneiss (B) and calc-silicate (D) rocks shows

strong leaching whereas the paleosols profiles developed on quartzo-feldspathic (C),

hornblende gneiss (F) and ultramafic rocks (G) shows low leaching (Figure- 5.17).

Strong loss of mobile cations and clay enrichment is typical of soils that form in warm

tropical and subtropical environments (Brady, 2002). The variations of leaching ratio

in the all studied profiles are shown in Figure- 5.17.

202

5.6.6 Chemical Index of Alteration (CIA)

Soil profiles characterized by high degree of weathering are enriched in hydrous clay

mineral phases. Another method can be used to measure the degree of chemical

weathering in paleosol profiles is the chemical index of alteration (CIA) of the profile

in terms given by Nesbitt and Young (1982) using molecular proportions:

( )

Based on description of Nesbitt and Young, (1982) Changes in CIA are reflected

mainly by changes in the proportion of feldspars and clay minerals or caused by grain

size sorting during original deposition of the parent material for the profile. Different

parent materials have different initial CIA values. The parental materials of the study

area are shown wide range of CIA for example, amphibolite (A) in Chikkahali shows

CIA value of 62.8 whereas calc-silicate (D) rock in Bettadabidu shows CIA value of

20.4 (Figure-5.18).

Except profiles developed on quartzo-feldspathic rock (G), and ultramafic rock in all

studied profiles significant increasing in CIA value of top horizon are observed this

result is an agreement with hydrolysis value obtain in same profiles. The changes in

these CIA values are illustrated in Figure-5.18. CIA values for the profile are more

than 80 suggesting the presumed parent material was weathered under intense

leaching conditions (Nesbitt and Young, 1982).

5.6.7 Chemical Index of Weathering (CIW)

Chemical Index of Weathering for the first time proposed by Harnois (1988), he

considers that the alteration index calculated on K2O-free basis will represent better

the intensity of weathering. Later on Condie, (1992) considers CIW as a best measure

of intensity of chemical weathering.

The chemical index of weathering measure the degree of weathering experienced by a

material relative to its source rock and increased with depilation of Na and Ca in soil

203

profile relative to Al (Harnois,

1988). The following equation is used in the

calculation of CIW:

( )

The CIW, just as CIA values are found to be maximum for paleosols developed on

amphibolite (A) in Chikkahali area (85) followed by hornblende gneiss (F) in

Gundlupet area. However, the gneiss (B) and quartzo-feldspathic (C) profiles which

showed low CIA values, are characterized by high CIW, suggesting the low CIA may

be due to post depositional enrichment of K2O in these profiles. Figure- 5.19 shows

variation of CIW index in all seven studied profile in and around Mysore district.

204

Figure- 5.13: Variation of salinization values in the selected Paleosol profiles in the

study areas.

205

Figure- 5.14: Variation of clayeyness values in the Paleosol profiles in the study

areas.

206

Figure- 5.15: The calcification parameter variation in the Paleosols developed on

different parent rocks.

207

Figure- 5.16: The hydrolysis parameter variation in the Paleosols developed on


208

Figure- 5.17: The leaching parameter variation in the Paleosols developed on


209

Figure- 5.18: The variation of CIA in the Paleosols developed on different parent

rocks.

210

Figure- 5.19: The variation of CIW in the Paleosols developed on different parent

rocks.

Documents

CHAPTER V Geochemistry - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/37106/8...5.3.1 X-Ray Fluorescence Spectrometry Collapsible aluminum cups were filled with 9 gm of boric