28

CHAPTER II

GEOLOGY OF DHARWAR CRATON

29

2.1 INTRODUCTION

A clear understanding of the physiographical, structural and lithological characteristic

features of an area play an important role in understanding the process of weathering

and soil formation. This chapter highlights the geological conditions of the Dharwar

Craton in general and the lithological characteristic features, structural alignment and

soil, in particular.

The Indian subcontinent covers approximately 5,000,000 km2. Although India is

connected geographically to the Eurasian continent, the subcontinent and Himalayan

sectors make up a distinct lithospheric plate. The Peninsular India is divided into five

discrete crusts namely Bhandar, Singhbum, Aravalli, Eastern Ghats and Southern

India.

2.2 GEOLOGY OF SOUTHERN INDIA

The Precambrian shield of southern India, of which the present study area forms a

part has been divided into cratonic nuclei of Dharwar, Singbhum and Bastar,

surrounded by mobile belts of successively younger ages (Radhakrishna and Naqvi,

1986). The Archaen terrain of southern India records geological events that occurred

essentially during 3.4 to 0.5 Ga. It can be divided into two principal terrains based on

the grade of metamorphism as: (1) southern high-grade granulites terrain and (2)

northern low grade granite-greenstone terrain. The boundary between these two

terrains appears to be a kind of transition which is superimposed across the structural

grain (Chadwick et al., 1993). The southern high-grade terrain encompasses large

areas in Tamil Nadu, Kerela and part of Karnataka and is essentially composed of

gneisses punctuated with rafts of supracrustal rocks. The rocks of the terrain exhibit a

polymetamorphic history, with the youngest event recorded at 500 m.y. which may be

correlated with the pan-African orogeny (Chacko et al., 1987). The northern low-

grade terrain is spread over major parts of Karnataka and Goa and parts of Andhra

Pradesh and is composed of several supracrustal (greenstone) belts surrounded by

gneisses and granitoids. The northern low-grade terrain has been referred to variously

as Dharwar Craton or Karnataka Craton and Dharwar Nuclei (Pichamuthu, 1985;

Drury et al., 1984; Rogers, 1985; Radhaakrishna and Naqvi, 1986 and

Mukhopadhyay, 1986). The central part consists of granite-greenstone terrain

30

characterized by green schist to lower amphibolite facies and is surrounded by a

mobile belt consisting of granulite facies, charnockite terrain and migmatitic gneisses,

well exposed in the eastern portion of the south Indian shield. In general, the south

Indian Peninsular region includes representatives of all the three principal rock

associations which characterize Arachean terrains, viz., (i) the high-grade associations

(granulites) of Tamilnadu and Kerala (ii) the granite-greenstone association (older

supracrustals) and, (iii) the Craton-basin association of (Dharwar). Perhaps in no other

part of the world, are the three associations brought together in such a well-knit

composite unit as in South India, affording excellent opportunities for a close study

and understanding of the stages in the evolution of the early crust. Since the study

area is located in the Dharwar Craton, some geological aspects of the Craton is

provided as prelude (Figure- 2.1).

31

Figure- 2.1: Generalized geologic and tectonic map of Indian shield (after Drury et

al., 1984).

32

2.3 DHARWAR CRATON

The Dharwar Craton (or Karnataka Craton) lying between longitude 72º 45´-80° and

latitudes 11º-19° is an elliptical region comprising of a number of subparallel

supracrustal belts and stringers, is set in a matrix of polyphasic gneisses and bordered

by granulites in the south and granites to the east (Radhakrishna and Naqvi, 1986;

Radhakrishna and Ramakrishnan, 1988). The available geochronological ages

spanning between 3.4 and 2.0 b.y.a. highlights the major early Precambrian events in

the Craton. The Karnataka Craton of the South Indian shield exposes numerous linear

greenstone belts covered by younger group of rocks in the North. The oldest group of

rocks forming the Craton was considered till recently as Dharwars, intruded

extensively by granite of different ages (Pichamuthu, 1962). The rocks of Super schist

are characterized by high grade metamorphism from upper amphibolites to

transitional granulite facies and have suffered intensive deformation and

migmatisation.

The term Dharwar (Karnataka) Craton was introduced by the geological survey of

India (1978), to accommodate the already known Dharwar super group (Dharwar

greenstone granite) and recently established Sargur Schist complex (Sargur type high

grade terrain). Till today, the existing nomenclature still being used by some workers,

viz., Dharwar greenstone granite, highly metamorphosed Dharwar greenstone

representing the Sargur high grade terrain is confusing, it is apparent that the prefix

Dharwar has become common to the cratonic counter parts. The Dharwar Craton is

split into Eastern and Western Cratons, with major differences in lithology and ages

of rock units. the dividing line being a steeply dipping mylonite zone interpreted by

Chadwic et al., (1992) as listric structure, and as a low angle thrust which becomes

shallow at depth as proposed by Kalia et al ., (1979). The Closepet Granite is a good

approximation of the western boundary (Ramakrishnan and Vaidyanadhan, 2008).

Chitradurga shear zone marks the boundary between Western Dharwar and Eastern

Dharwar Craton apart from Closepet Granite. The Chitradurga shear zone is a narrow

geosyclinal belt which extends from Gadag in the north to Shrirangapatna in the

south, for a length of 460km. The belt attains a maximum width near Chitradurga

(Nath et al., 1976; Drury et al., 1984; Chadwick et al., 2000). These Cratons have a

billion years of early history of the earth shown in Figure- 2.2.

33

Figure- 2.2: Geology of the western and eastern Dharwar Craton (after Rogers,

1990).

34

a) Western Dharwar Craton

The Western Dharwar Craton (WDC) is located in southwest India and is bound to the

east by the Eastern Dharwar Craton (EDC), to the west by the Arabian Sea, and to the

south by a transition into the so-called “Southern Granulite Terraine”. The remaining

boundary to the north is buried under younger sediments and the Cretaceous Deccan

Traps (Figure- 2.3). The division between the Western and Eastern Dharwar Cratons

is based on the nature and abundance of greenstones, as well as the age of surrounding

basement and degree of regional metamorphism (Rollinson et al., 1981).

The western block of Karnataka Craton comprises of Holenarsipur, Bababudan,

Shimoga-North Kanara, and Chitradurga- Gadag belts supracrustal (schist) belts. The

available radiometric dates of supracrustal rocks and gneisses appear to be consistent

with this broad two-fold division, wherein, the Sargur group of rocks have been

deposited during 3130-2960 m.y. (Nutman et al., 1992) and supracrustal rocks of

Dharwar supergroup accumulated during 2900-2600 m.y. (Taylor et al., 1984). The

polyphase migmatitic gneisses yielded radiometric ages ranging from 3.4 - 2.5 Ga.,

but large areas recorded ages of 3.0 Ga. The supracrustal rocks and Peninsular

gneisses are further intruded by k-rich granites which are 2.5 Ga. old (Taylor et al.,

1984 and bhaskar Rao et al., 1992). The status of Super group as a separate unit has

however been disputed by Naha et al (1993), who questioned the validity of attaching

stratigraphic significance to the Peninsular gneisses which constitutes a polyphase

gneiss evolved over a long span of time ranging from 3.3 -2.9 Ga. High grade

supracrustal rocks underlying the basal unconformity have been referred to as

“Sargurs” by Swami Nath and Ramakrishnan (1981), (Figure- 2.4).

The younger Dharwar super group has been subdivided into (a) the lower Bababudan

group and (b) the upper Chitradurga group and (c) Shigegudda schist belts based on

the presence of a thin persistent oligomict quartz pebble conglomerate horizon

marking the unconformity between these two groups (Figure- 2.5). The supracrustal

rocks of Sargur occur as thin slivers and tectonic slices set in Peninsular gneiss and

are mainly confined to the southern fringes of the Karnataka Craton. In the southern

parts of Karnataka Craton, the supracrustal rocks of the Sargur group have been

subjected to granulite facies metamorphism. Radimetric ages of detrial zircon present

in quartztes led Chadwick et al., (1986) and Nutman et al., (1992) to propose a sialic

35

basement for the Sargur. The Sargur group encompasses a diversified group of

volcanic and sedimentary lithologies, represented by ultramafic-mafic volcaniv rocks,

pellites, quartzites, impure carbonates, iron formation and intrusive ultramafic-mafic

and gabbro-anorthosite complexes (Swaminath and Ramakrishnan, 1981). Further,

they reported concordant contact of the Sargur enclaves with the surrounding gneisses

and migmaties implying their involvement in ductile deformation along with the

gneisses. The greenstone belts of the Western Block are characterized by mature,

sediment-dominated supracrustals with subordinate volcanism and are recrystallized

in intermediate pressure Barrovian metamorphism. However, development of

greenstone belts in the western block of the Dharwar Craton proceeded through three

major depositional cycles of volcanism and sedimentation, terminating with the

intrusion of syn- to post-kinematic granites on minor scale.

36

Figure- 2.3: Geological map of the Western Dharwar Cratons (after Naqvi and

Rogers, 1987; Ramakrishnan and Vaidyanadhan, 2008).

37

Figure- 2.4: Geological map of Western Dharwar Craton (Swami Nath and

Ramakrishnan, 1981; Naqvi and Rogers, 1987).

38

Figure- 2.5: Geological map of Sargur Supracrustal suite (after Swami Nath and

Ramakrishnan, 1981).

39

b) Eastern Dharwar Craton

The EDC is bounded to the north by the Deccan Traps and the Bastar Craton, to the

east by the Eastern Ghats Mobile Belt, and to the south by the Southern Granulite

Terraine (Balakrishnan et al., 1999). The Craton is composed of the Dharwar

Batholith (dominantly granitic), greenstone belts, intrusive volcanics, and middle

Proterozoic to more recent sedimentary basins (Ramakrishnan and Vaidyanadhan,

2008), (Figure- 2.6).

The supracrustal belts of the Eastern block of the Dharwar Craton are smaller in size

than those of the western blocks which are surrounded by gneisses and granites. The

prominent greenstone belts of the Eastern Block include Kolar, Sandur and Hutti.

These belts contain supracrustal rocks essentially made up of volcanic rocks with

subordinate amounts of sedimentary rocks composed of quartzites, polymict,

conglomerate, carbonates, BCF/BIF and Mg-rich peletic rocks and phyllites.

Radhakrishna (1984) considered the greenstone belts of the Eastern Block as “older

greenstone belts” that are either older or equivalent to the Bababudan group of the

western block. The supracrustal rocks are intruded by 2.5 Ga. old syn-to late/post

tectonic granites. However, metabasalts from Kolar schist belt yielded an age of 2.7

Ga., indicating that they are contemporaneous with the Chitradurga group of the

western block (Rajamani et al., 1981 and 1985). A majority of the granitoids and

gneisses of the Eastern Block yielded an age ranging from 2.6 to 2.5 Ga and are

attributed to mantle sources with limited crustal Eastern Block (closepet granite) are

reported to be generated by the melting of metasomatised mantle source (Martin et

al., 1994; Nutman et al., 1996).

Several geochemical studies have been conducted by Rajamani et al., (1990), Iyer and

Vasudev (1979) on the volcanic rocks of Kolar and Hatti schist belts. The volcanic

rocks of Kolar schist belt are composed of Komatiitic-tholeiites and were derived

from a shallow mantle source. The volcanic rocks of the Hutti schist belt are

composed essentially of thoeiitic basalts and minor rhyolites. According to Martin et

al., (1993), the post-kinematic granites have been generated by the melting of

metasomatized mantle source.

40

Figure- 2.6: Geological Map of Eastern Dharwar Craton (Modified from Naqvi and

Rogers, 1987).

41

As regards mineralization, the western block is characterized by copper, iron and

manganese mineralization, whereas the Eastern Block is known for gold, iron and

manganese mineralization. Based on a classification given by Radhakrishna (1983)

the supracrustals of Dharwar Craton is classified into:

1) Ancient supracrustal, 2) Older and younger Gneissic complex, 3) Auriferous schist

belt, 4) Larger schist belt 5) Younger Granites, 6) Granulites, 7) Younger intrusive-

Dyke Swaps, 8) Great Eparchaen Intervals, 9) Proterozoic Sedimentation, 10) Deccan

Traps, and 11) Laterites. Brief descriptions of the above groups are explained as

bellow:

2.3.1 Ancient Supracrustal (Sargur Type)

The oldest rock dated so far in Karnataka are a group of grey gneisses giving an age

ranging from 3000-3400 m.y. these are termed ancient supracrustal and includes the

Sargur, Holenarasipur, Kunigal, Ghattihosahalli, Gurgunta Schist belt, Aladahalli,

Kalyadi, Krishnarajapet and Nuggehalli Schist belts (Radhakrishna and

Vaidhyanathan, 1994). However, the term “schist belt” is more appropriate, as it

emphasizes the unique schistose character of the Archaean volcano-sedimentary

sequences (Radhakrishna and Naqui, 1986). The schist belts consisting of the Sargur

group of rocks, being studied in the transition zone between northern lower-grade and

southern higher-grade terrain, have also been subjected to upper amphibolites to

granulites grade metamorphism 2.5 Ga. ago (Srikantappa et al., 1985).

The Sargur group of rocks occur as independent enclaves, thin silvers and tectonic

slices within the Peninsular gneisses confined mainly to the southern fringes of the

lower-grade terrain of the Dharwar Craton and occur within the transition zone

between the northern lower-and southern higher- grade terrain. The basement for

those rocks are not identified anywhere but sialic basement has been inferred, based

on detrital zircon grains present in the quartzite of the Sargur group (Chadwick et al.,

1986 and Nutman et al.,1992).

Important lithotectonic linear belts of Sargur group is characterized by a lack of basal

unconformity with the associated of diversified igneous and sedimentary rocks. They

include ultramafic-mafic volcanic rocks, pellites, quartzite, impure carbonates, iron

formation and ultramafic-mafic intrusive bodies (Swaminath and Ramakrishan, 1981).

42

Volcanic rocks of the Sargur group are composed of komatiite-tholeiites suite, in

which the komatiite predominates over the tholeiites. Drury (1983) suggested that the

parent melts for the ultramafic- mafic volcanic rocks were generated through melting

of mantle diaper at a depth of about 70 Km in a back –arc environment. However; the

study by Rajamani (1990) considered that the ultramafic-mafic volcanic rocks of the

Sargur group are not genetically related either to common parent magma or to a

common source. According to him, the komatiitic magma originated from deeper

mantle source at depths of about 100 Km and tholeiitic magma formed at a depth of

50 Km.

2.3.2 Older and Younger Gneisses Complex

The gneissis lying within the state is nucleus form, occupied about 35% of the area

and exhibited an extreme diversity of composition owing their origin to several

tectono- thermal events with a large influx of sialic material (B.P.Radhakrishna-

1994). Older and Younger Gneissic Complex was further divided into three groups

(Radhakrishna and Naqvi, 1986) which are as follow:

A complex of banded gneisses showing multiple deformations.

A suite of much less deformed, nearly massive gneisses of broadly similar

composition but are apparently developed subsequently to the deformation

that effected the earlier banded gneisses and

Late tectonic potassium (k) rich granitic gneisses.

These extensive groups of gray gneisses are designated as the “Older Gneissic

Complex” acting as the basement for an extensive belt of schists. The Gneisses

records whole rock age ranging from 3400 m.y. to 3000 m.y. (Radhakrishna B. P. and

Naqui, 1986) A younger group of gneissic rocks are found in the eastern parts of the

state. The rocks belonging to this group are aged from 2500-2800 m.y. mostly of

granodioritic and granitic in composition.

2.3.3 Auriferous Schist Belts (Kolar Type)

“Auriferous schist belt” are the belts, which are largely volcanic and gold bearing.

They are mainly igneous in character with a subordinate sedimentary intercalation.

The most characteristic feature of these rocks is in their auriferous nature. They are

well developed in the eastern part of the Karnataka state.

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2.3.4. Larger Schist Belts (Dharwar Type)

These are the prominent schistose rocks of Karnataka named “Dharwar schist belt”

which has been given a super group status. They are of late Archaean and belong to

the age group of 2900-2600 m.y. the two main divisions in this super group are

recognized. The older is mainly igneous in character and named as “Chitradurga

group”. Overlying this is a more extensive group of schistose, largely sedimentary in

nature, composed of conglomerates, quartzite, limestone, graywacke and associated

manganiferrous and ferruginous cherts. The “Rani Bennur group” is the youngest

series of sediments, mostly greywacke in composition and intercalated with cherty

iron formation.

2.3.5 Younger (Closepet) Granite

The liner belt of Closepet Granite is having a length of nearly 500 kms and an average

width of 20-25 Kms. They are the most prominent of the younger granite. The trend

of these Granites extends in a North-South direction and parallel to the structural

grains of the host rock. These granites being the youngest, in point of age in the

Arachaean complex of Karnataka is termed as ‘Youngest Granites’and is also termed

as ‘Closepet granite’, after the town of Closepet where the rock types were first

recognized (Radhakrishna B.P., 1986). The geocronological data suggest that the two

major events experienced in the emplacement of Closepet Granite at 2400-2600 m.y.

and 2000 m.y. (Karamuddin and Stueber, 1976 and Jayaram et al., 1983), Chitradurga

and Banawara groups belongs to the same age. The most characteristic rock type of

this class is coarse-grained porphyritic granite with large-sized pophyroblasts of pink

and grey potash feldspar.

2.3.6 Granulites

In the Southern part of the Dharwar Craton are granulites facies rocks represented

with extensive development of Charnokite and pyroxene granulite. A vast granulite-

migmatitic complex, known as the Coorg granulites complex (CGC), is exposed in the

western part of Mysore, which is mainly composed of Peninsular gneisses,

migmatites, basic and ultra basic intrusive, high grade schist and granulite-facies

rocks. Geochronological data indicates an age of 2500-2700 m.y. (Ramiengar et al.,

1978) these are alternation of the older gneisses.

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2.3.7 Younger Intrusive-Dykes Swamps

Younger intrusive are the dyke-formation formed at the close of the Archaean era,

ranging from doleritic to alkaline composition with both NS and SW trending dykes

traversing rocks of earlier ages. These ultramafic of doleritic composition are found in

the Eastern parts of Karnataka (Bangalore and Mysore) which are younger and in all

probability unrelated to the dolerite dykes but may be connected with younger granitic

activity. The majority of the dykes are younger than 2400 m.y. the alkaline

composition consists of Epidiorite, Quartz dioritend olivine diorite with local

development of Pyroxene and Gabbro. The alkaline dykes are unrelated to dolerite

dykes and their age is around 800 m.y.

2.3.8 Great Eparchaean Intervals

A long period of stability of more than 1000 m.y. duration exceeds the Archaean,

during which the earlier rocks were exposed to the action of winds and water. This

period is called as Eparchaean unconformity.

2.3.9 Deccan Traps

The next major event is the burst of volcanic activity at the end of the cretaceous-

dawn of tertiary era. Deccan Trap rocks, especially basalts, cover a substantial part of

northern Karnataka particularly the districts of Belgaum, Bidar, Bijapur and Gulbarga.

This is represented by horizontal sheets of lava piling one upon the other over a

thickness of nearly 2 Km and extending over an area of 5,000,000 Km2. The burst of

volcanic activity was sudden and continues with hardly any interval between the

flows. The volcanic episode was short not exceeding more than a million years. The

fossils embedded in these suggest a tertiary age (Radhakrishna and Vaidyanatha,

1997). The western margin close to the coast was affected by large-scale dyke

intrusion. The dyke assigned an age around 65 m.y. connects them with Deccan

volcanic activity.

2.3.10 Laterite

Over the Deccan trap capping of laterite is found which probably started forming at

cessation of Deccan volcanic activity an early tertiary and are continuing to form even

45

today. The narrow coastal belt between the coast line and the precipitous edge of the

Western Ghats in a plain of marine denudation and is covered by the extensive

capping of detrital and residual laterite.

2.4 DHARWAR SUPRACRUSTAL ROCKS

Based on the supracrustal lithological relationship between the Peninsular gneiss and

the supracrustal rocks, Swami Nath and Ramakrishnan (1981) classified the

supracrustal rocks of Dharwar Craton into older Sargur Group and younger Dharwar

Supergroup. The Dharwar Supergroup was further divided into two Groups:

Bababudan Group and Chitradurga Group. Major schist (supracrustal) belts of the

Karnataka Craton are composed of lithologies belonging to Dharwar Supergroup. In

the Dharwar Supergroup, the supracrustal rocks in unconformably overlie the

basement Peninsular gneiss, but in Sargur group the Peninsular gneisses posses an

intrusive contact and hence, are older than the gneisses. The status of Sargur as a

separate group of older rocks has been accepted and adopted by many geologist

(Radhakrishna, 1976; Radhakrishna, 1983; Taylor et al., 1984; Mukhopadhyay, 1986;

Radhakrishna and Naqvi, 1986; Basker Rao, 1986; Radhakrishna and Ramakrishnan,

1988). Inspite of acceptance of the “Sargurs” as a distinct Group of rocks older than

Dharwars, a number of uncertaiities still prevail as far as geochronological, structural,

staratigraphic and tectanometrorphic relations are concerned.

2.4.1 Sargur Group

The Sargur has Swami defined as high grade supracrustal rocks underlying the basal

unconformity of the Dharwar Craton (Nath and Ramakrishnan, 1981). The

unconformities are marked by a thin persistent oligomict quartz pebble conglomerate

horizon, well exposed in Bababudan, Chitradurga, Western Ghats and Shigegudde

schist belts (Figure- 2.4). The Sargur Supracrustal complex has been disrupted by

broadly syn-tectonic emplacement of tonalitic and allied suites of Peninsular gneiss

(Chadwick et al., 1989). The Sargur Group of rocks is metamorphosed ranging from

middle amphibolites facies in central Karnataka to upper amphibolites and granulie

facies in Southern Karnataka (Chadwick et al., 1989). Age of Sargur is tentatively

considered to be 3.4-3.0 b.y. (Nath and Ramakrishnan, 1981; Radhakrishna, 1983;

Taylor et al., 1984; Radhakrishna and Ramakrishnan, 1988).

46

Sargur Group found as belts enclaves, bands and stringers, are traced near Sargur,

Amble, Alathur, Nanjangud, Talkad, Gundlupet, Aladahalli, Kalyadi, Sakalespur,

Madikeri, Naggihalli, Krishnarajapet, Kunigal and other areas. According to Swami

Nath and Ramakrishnan (1981), Sargur group lithologies include quartzite, quartz-

fuchsite-muscovite schists, bedded barites sillimanite-garnet-staurolite-kyanite-

graphite-corundum-quartz-biotite schists, crystalline limestones, dolomites, calc-

silicate rocks, amphibolites (metabasaite), iron stones (oxide and silicate facies BIF)

meta ultramafic and anorthosites. Structural features of Sargur group rocks are

complex. The Sargur enclaves represent elongated and locally faulted synformal keels

and antiformal hinges. The enclaves and belts have concordant contacts with the

surrounding gneisses and migmatites, implying their involvement in ductile

deformation along with the gneisses (Swami Nath and Ramakrishnan, 1981).

2.4.2 Dharwar Supergroup

The Dharwar supercrustal is deposited unconformably over a sialic basement of

tonalitic and granitic “Peninsular Gneiss” (Chadwick et al., 1981). The supracrustal

rocks of Dharwar Supercrustal are exposed as number of schist belts; prominent

among then are: Bababudan, Western Ghat, Chitradurga, Shigegudda, Shimoga-North

Kanara-Goa, Sandur, Kolar&Hutti schist belts. Total thickness of these Dharwar

schist belts is estimated to be 6 to 7 km (Radhakrishna and Ramakrishnan, 1988). Age

of the Dharwar Supergroup rocks is tentatively fixed in the range of 3.0-2.6 b.y.a.

(Radhakrishna, 1983; Taylor et al., 1984; Radhakrishna and Ramakrishnan, 1988).

The volcanic and sedimentary rocks in the Dharwar schist belts display highly

variable compositions; lithofacies and stratigraphic thickness.They were probably

deposited in variably subsiding and progressively evolving basins in an intracratonic

or continental margin setting (Bhaskar Rao, 1986). The volcanic rocks of the Dharwar

Supergroup evolved from predominantly tholeiitic in the lower units to calcalkaline

affinities in the upper units (Bhaskar Rao and Drury, 1982). The study by Naqvi

(1985) has determined the sedimentary rocks of Dharwar Supergroup are represented

by (1) Chemogenic BIF (volcanogenic-volcanoclastic-exhalative sedimentary suite),

(2) dettrial mature quartzite-conglomerate-metaarkose-carbonaceous shale suite and

(3) graywack-phyllite –carbonate-BIF suite. The chemognic sediments include

fuchsite quartzite, oxide-carbonates and manganese formations which are spread in all

47

groups but with differing relative abundance. Volcanoclastic sediments include truff,

volcanobreccia and probably ash beds. Detrital mature conglomerate and quartzite are

found in Bababudan Group. Graywackes and graywacke conglomerate are widespread

in the Chitradurga Group. More than 70% of the belt is made up of graywackes and

greywacke conglomerate (Naqvi, 1985).

2.4.2.1 Bababudan Group

Bababudan Group of rocks are exposed mainly in Bababudan, Westearn Ghats,

Shigegudda, northern Holenarasipur and Yadiyur-Karighatta arm of Chitradurga

schist belt. Bababudan Group represents a typical mafic platformal association ending

up in prominent iron ore (BIF) cycle. Manganiferous sediments and carbonate rocks

are conspicuous by their absence.the basal quartz-pebble conglomerate is known to be

pyritiferous and uraniferous. The Bababudan sediments and Volcanics suggest

nearshore to shallow marine and subaerial to shallow marine environment

respectively (Chadwick et al., 1985). The rocks of Bababudan Group are

metamorphosed upto lower amphibolites facies (garnet isograd) at the borders and

greenscist facies at the core portions (Swami Nath and Ramakrishnan, 1981).

2.4.2.2 Chitradurga Group

Chtradurga Group of rocks, mainly exposed in Chitradurga, Sandur and Shimoga-

North Kanara-GOA shist belts, overly an oligomict or polymict granite clast

conglomerate, which are deposited on a basement of tonalitic-granitic gneisses

(Swami Nath and Ramakrishnan, 1981). The basal beds are overlain by basic meta-

lavas and amphibolites, interbedded with cross quartzites and siliceous phyllites and

further by polymict conglomerate (Taylor conglomerate), BIF, chert pebble

conglomerate and thick pile of greywackes (Chadwick et al., 1981). Naqvi et al

(1988) reported that the graywackes have been derived from both continental and

contemporary volcanic source .according to them, a mixied source consisting of

tonalitic, feldspathic and ferruginous quartzites (5-10%) can account for the observed

composition of the graywackes. sedimentation and volcanism is known to have

proceeded in deep marine environments (Bhaskar Rao, 1986). The rocks of

Chitradurga Group are metamorphosed to lower amphibolites facies in border zones

and greenschist facies in the central parts.

48

2.5 PENINSULAR GNEISS AND GRANITE

Peninsular Geisses are a collection of heterogeneous acidic rocks (migmatites,

gneisses and granitoids) that were evolved at different periods during a long span of

time ranging from 3.3 to 2.6 b.y.a. The compositions of these gneisses have

undergone a change from trondhjemitic-tonalitic to granodiorite-granite through

reactivation, melting and potash metasomatism (Naqvi and Rogres, 1983). The major

phase of the Peninsular gneiss exhibits intrusive relationship with the Sargur group of

rocks, Sargurs show concordant contacts with the associated gneisses. It is also

characterized by zircons of igneous morphology and low potassic content

(Mukhopadyay, 1986).three major phases of emplacement of Peninsular Gneisses

were recognized so far.

Chadwick et al (1981) demonstrated that, deformation of the Dharwar Supracrustal

mainly resulted due to variable displacement and uplift of the basement gneisses.

Vishwanatha and Ramakrishnan (1976) visualized two blocks within the Arachaean

compomenmt of the Karnataka Craton. According to them, the dividing line between

these two blocks viz., Weastern and Eastern and is a N-S trending fault zone , now

occupied by a linear batholiths of porphyritic granite (Closepet granite).

In the western block of the Dharwar Craton, the basement-cover relationship between

the Peninsular Gneiss and rocks of the Dharwar supracrustals is more or less clear.

Schist belts of the Eastern block, however, show ambiguous and controversial

relationship with the basement gneisses (Sandur, Kolar and Hutti schist belts). A

number of granite bodies belonging to the third phase of evolution of Peninsular

Gneiss complex form topographical landmarks in the Craton. Closepet granite is a

prominent meridional batholith extending in a north southerly direction for about 500

km in the eastern part of the Karnataka Craton. It is essentially porphyritic granite

with gray and pink varieties.A major fault zone has been recognized along the eastern

margin of the Closepet granite belt (Kaila et al., 1979) the granitic area dividing the

craton into Western and Eastern blocks, is considered to be a low pressure zone

(Vishwanatha and Ramakrishnan, 1976).

49

Radhakrishna (1956) proposed that these granites have been formed by granitisation

of the Peninsular Gneiss by alkali solutions. Divakara Rao et al. (1972) envisaged

palingenesis of Peninsular Gneiss followed by alkali metasomatism.

2.6 STRUCTURES

The supracrustal rocks of the Dharwar supergroup have been affected by their phase

of deformation (to Srinvasan and Naha, 1990). The earliest deformation give rise to

isoclinals folds with well developed axial plane schistosity .During the second phase

of folding, the earlier axial planes were involved in co-axial folding leading to hook-

shaped interference patterns. The investigation by Rama Rao (1936, 1962) showed

that the Dharwar schist belts as ramnants of a huge synclinorium plunging south.

Pichamuthu (1951, 1953) has interpreted it to be anticlinorium plunging NNW.

Radhakrishna (1984) summarized that the various schist belts of the Dharwar

supergroup are individual entities and not eroded remnants of once continuous

regional mega structure.

Drury and Holt (1980) proposed a number of shear belts representing, “zones of high

strain” in the Karnataka Craton. They suggested that the NNW trend of the

supracrustal belts reflect the trend of steep ductile shear belts, mostly having sinstral

sense of movement. Within these belts, the axial traces of the preexisting folds were

drawn into parallelism with the folds of the schist belts. Drury (1983) suggested that

the shear strain in the linear belts become pronounced to the south with concomitant

widening of the shear belts.

According to Chadwick et al (1989) the structures of the Dharwar Super group are

dominated by a set of mainly open to tight upright synclines. Their trends are variable

and the plunge of their axes range from sub-horizontal to sub-vertical.

2.7 METAMORPHISM

The progressive change of regional metamorphism from north to south in the Dharwar

Craton has been recognized by Rama Rao (1936). Pichamuthu (1974) related this

increase in grade of metamorphism to increasing depth of burial.

50

The southerly increasing, progressive nature of regional metamorphism is also

corroborated by the regional study of mineral chemistry of potash feldspar, garnets

and amphiboles (Ananta Iyer 1973; Ananta Iyer and Kutty, 1974, 1976). The north-

south variation in metamorphism from core to margin in individual schist belts

(Swami Nath and Ramakrishnan, 1981; Radhakrishna, 1984). Vishwanatha and

Ramakrishnan (1976) reported two basic types of metamorphic facies. On the western

side of Closepet granite an intermediate pressure, and on the eastern side, low

pressure metamorphic assemblages were recognized.

51

Table- 2.1: Stratigraphy of Western Dharwar Craton (after Swami Nath &

Ramakrishnan 1981).

Dharwar

Supergro

up

(2600-

2800Ma)

Chitradurga

Group

Ramebenur

subgroup

Graywacks with BIF,polymict conglomerate ,mafic-felsic volcanic

Manganese and iron formation ,

mafic –felsic

stromatolitic carbonates ,biogenic

volcanic with

chert ,pelites quartzite and

BIF,phyllites

,polymict conglomerates

( basi centre)

(basin margin)

Talya/Kaldurga conglomerate =metabasalts and siliceous phyllites

of Jagar valley

Disconformity

BIF with phyllites and rare ultramafic –mafic sills

Metabasalt,felsic volcanic(Galipuje felsic )ultramafic

schists,layered basic complexes ,siliceous phyllite,cross-bedded

quartzite (Kaimara ,tanigebail)

Metabasalt ,gabbros,ultramafic schists,local BIF,phyllites,cross-

bedded quartzite (Lakya)

Metabasalt ,gabbros,ultramafic schists,phyllites

,quartzites,basalquartz pebble conglomerate (Kartikere

conglomerate)

Deformed angular unconformity

Peninsular gneiss with trondjhemite –granodiorite

plutons(>3000Ma)

Intrusive /Tectonic Contants

Ultramafic-mafic layered complexes ,tholeiitic

amphibolites,kamatiites,BIF

Quartzites,pelites,marbles,and calcsilicate rocks

Intrusive /Tectonic Contacts

Gorur Gneiss (3300-3400 Ma)

Vanivilas

Subgroup

Bababudan

Group

Mukaingiri

formation

Santaveri

fornation

Allampura

Formation

Kalasapura

Formation

Sargur Group

(3100-3300Ma

52

2.8 SOILS

Soils are the fundamental resource supporting agriculture and forestry, as well as

contributing to the aesthetics of a green planet. Soil is vital natural resource on whose

proper use depend the life supporting system of a country and the socio-economic

development of its people. However, the capacity of the soil to produce is limited and

limits to production are set by intrinsic characteristics, agro-ecological setting, use

and management. Different geological formations lead to the formation of different

types of soils.

2.8.1 Major Soil Types of India

Indian Council of Agricultural Research (ICAR) has divided Indian soils into eight

major groups. Some dominant groups of Indian soil, classified according to soil

taxonomy and chemical property are mentioned below:

1) Red soil: Alfisol, Inceptisol and Ultisol

2) Lateritic soil: Alfisol, Ultisol and Oxisol

3) Black soil: Vertisol, Inceptisol and Entisol

4) Alluvial soil: Entesol, Inceptisol and Alfisol

5) Desert soil: Entisol and Aridisol

6) Forest and Hill soils: Alfisol

2.8.1.1 Red Soil

The red soils of India, including red loams and yellow earths, occupy about 3.5 lakh

sq km– 10.6% of the total land area of the country and extend over a large part of

Chhotanagpur plateau, Telangana, Nilgiris, Tamil Nadu, Karnataka, Andhra Pradesh

and periphery areas of Deccan Plateau. In the north and north-east these extend into

and include great part of the Santhal Parganas of Bihar; Birbhum, Bankura and

Midnapur districts of West Bengal; Khasi, Jaintia, Garo and Naga Hills areas of

Assam; Mirzapur, Jhansi, Banda and Hamirpur districts of Uttar Pradesh;

Baghelkhand division of Madhya Pradesh and Aravallis and the eastern half of

Rajasthan. The red colour is due to diffusion of iron in the profile. The main features

of these soils, besides their lighter texture and porous and friable nature, are:

53

(a) The absence of lime (kankar) and free carbonates, and

(b) The usual presence of soluble salts in a small quantity, not exceeding

0.05 percent.

They are divided into two broad classes: (1) the red loams, characterized by a cloddy

structure and the presence of only a few concretionary materials; and (2) the red earth

with loose top-soil friable but rich secondary concretions of a sesquioxidic clayey

character. The soils have undergone excessive weathering and very low amount of

decomposable mineral hornblende.

They are mainly formed due to the decomposition of ancient crystalline rocks like

granites and gneisses and from rock types rich in minerals such as iron and

magnesium.

2.8.1.2 Lateritic Soil

They are composed of a mixture of hydrated oxides of aluminium and iron with small

amounts of manganese oxide. These soils occupy an area of about 2.4 lakh sq km in

India. The laterite is specially well-developed on the summits of the Deccan Hills,

Karnataka, Kerala, Tamil Nadu and hilly regions of Assam, Rajmahal hills and

Chhotanagpur plateau, etc.

Laterite soil is formed by weathering of lateritic rocks, low temperature and heavy

rainfall with alternating dry and wet periods. The laterite and lateritic soils are

characterized by a compact to vesicular mass in the sub-soils horizons composed

essentially of mixture of the hydrated oxides of aluminium and iron. These soils are

deficient in potash, phosphoric acid and lime. On higher levels these soils are

exceedingly thin and gravelly, but on lower levels and in the valleys they range from

heavy loam to clays and produce good crops, particularly rice.

The laterite soils in Karnataka occur in the western parts of Shimoga, Hassan, Kadur

and Mysore districts.

2.8.1.3 Black Soil

They contain a high proportion of Calcium and Magnesium Carbonates and have a

high degree of fertility. Black soils spread over an area of 5.4 sq. km., i.e. 16.6 % of

54

the total land area of the country and are mainly found over the Deccan lava tract

(Deccan Trap) including Maharashtra, Madhya Pradesh, Gujarat and Andhra Pradesh.

These soils are found in the river valley of the Narmada, Tapi, Godavari and Krishna.

These soils have been formed due to the weathering of the lava rocks. This is also

known as the Regur soil and Cotton soil. These soils may be divided into three

groups: (1) deep and heavy; (2) medium and light; and (3) those in the valleys of

rivers flowing through Sargur area.

The main features of the black soils are: (1) depth- one to two or several feet deep; (2)

loamy to clayey in texture; (3) cracking heavily in summer, the cracks reaching up to

more than three or four feet in depth, especially in the case of heavy clays; and (4)

containing lime kankar and free carbonates (mostly CaCO3) mixed with the soil at

some depths. These soils are often rich in montmorillonitic and beidlite group of

minerals. In regions of fairly high and evenly distributed rainfall the zone of carbonate

accumulation is found deeper in the profile and sometimes incorporated with horizon

C.

2.8.1.4 Alluvial Soils

They are depositional soils, transported and deposited by rivers and streams. This is

the largest and agriculturally most important group of soils. Various types of alluvium

are classed as alluvial, e.g., calcareous soils, saline and alkali soils, and coastal soils.

The alluvial soils occur mainly in the southern, north-western and north-eastern parts

of India: the Punjab, Uttar Pradesh, Bihar, West Bengal, parts of Assam, Orissa, and

coastal regions of southern India including the local deltaic alluvia. It covers about

22.16 per cent of land area of the country. They support a variety of crops, including

rice, wheat and sugarcane.

There is no marked differentiation into the various horizons, and the profile is often

characterized by the absence of stratification. The surface soil is generally grey,

varying from yellow to light brown, the intensity of colour increasing with the depth.

The immature soil near the rivers is calcareous and light brown in colour with salt

impregnation.

55

2.8.1.5 Desert Soils

They occur mostly in dry areas and its important content is quartz a large part of the

arid region in Rajasthan and part of Haryana, lying between the Indus and the

Aravallis and covering an area of about 1.4 lakh sq km, is affected by desert

conditions of recent geological origin. This part is covered under a mantle of blown

sand which inhibits the growth of soils. Low rainfall and high temperature are reasons

for the formation of this soil. Desert soil contains 90% of sand and 5% of clay. It

contains rich percentage of soluble salts, but lack in organic matter.

2.8.1.6 Forest and Hill Soils

They are high in organic matter (Nearly 22-23 per cent of the total area of India is

under forests). The formation of forest soils is mainly governed by the characteristic

deposition of organic matter derived from the forest growth. Broadly two types of

soil-formation may be recognized (1) soils formed under acid conditions with

presence of acid humus and low base status; and (2) soils formed under slightly acid

or neutral condition with high base status which is favourable for the formation of

brown earths.

The soils of the hilly districts of Assam are of fine texture and reveal high content of

organic matter and nitrogen, perhaps due to its virgin nature. Their chemical and

mechanical composition show great variations.

2.8.2 Soil Types of Karnataka

As per the latest updated soil survey data, the soils of Karnataka have been broadly

classified under nine groups. Based on taxonomic classification, the soils of

Karnataka are grouped into7 orders, 12 suborders, 27 great groups, 47 subgroups and

96 soil families. Of the total area of Karnataka, 27% is covered by Alfisols, 25% by

Inceptisols, 16% by Entisols, 15% by Vertisols, 8% by Ultisols, 5% by Aridisols and

1% by Mollisols. An area of about 4% is miscellaneous land type and that includes

rocky lands, water bodies and urban area (Figure- 2.7, 2.8). The characteristics and

distribution of these nine soil groups in different parts of Karnataka are as follows:

56

2.8.2.1 Shallow Black Soils

These soils are usually encountered on undulating ridges in the Deccan trap region

and to some extent on schist and lime stone upland region of Karnataka, occupying

areas in the north and north-west parts of the districts of Belgaum, Bijapur, Gulbarga

and Bidar.

These are shallow (less than 23 cm), dark grayish brown, and dark brown to dark

reddish brown, usually calcareous, with gravelly clay loam to clay in texture. They are

neutral to weakly alkaline and have moderate to high water holding capacity with

high cation exchange capacity (CEC).

The clay mineral is dominantly montmorillonitic. These soils are classified under the

orders Entisols and Inceptisols with sub-orders Orthents and Ochrepts.

2.8.2.2 Medium Black Soils

These soils usually occur in the Deccan trap, schist, lime stone and shale region of the

state, occupying areas in parts of Bidar, Gulbarga, Bijapur and Belgaum districts and

to some extent on Peninsular gneiss areas in Raichur, Chitradurga and Dharwad

districts.

These soils are moderately deep to very deep (23-90 cm), dark to very dark in grayish

brown, dark reddish brown or black in colour, usually calcareous, cracking, clayey

soils. These are highly moisture retentive, neutral to alkaline, and well supplied with

bases. They contain high percentage of clay dominated by montmorillonitic type of

mineral. These are moderately well drained with slow permeability. Heavy cracking

in dry periods, typical wedge shaped blocky structure and prominent slickensides in

the sub-surface horizons are quite common. The soils are classified under the orders

of Inceptisols and Vertisols with sub-orders Ochrepts and Usterts.

The soils are fertile and produce good yields when moisture is not limiting but

moderately susceptible to erosion.

57

2.8.2.3 Deep Black Soils

These soils occur in Deccan trap lime stone regions, in parts of Gulbarga, Bijapur and

Belgaum districts and considerable areas in parts of Raichur, Bellary, Dharwad,

Chitradurga, and Mysore districts. These are very deep (more than 90 cm), dark

brown, dark greyish brown to very dark grey or black in colour. The texture is usually

clayey throughout the profile. These are calcareous and are weak to strong alkaline,

highly cracking montmorillonitic clayey soils.

These are highly moisture retentive and moderately well drained to imperfectly drain

with low to very low permeability. A loose, crumb to granular surface mulch, gilgai

micro relief, prominent intersecting slickensides and typical sub-angular to angular

blocky structure are common in these soils. These soils are classified under the order

Vertisols with sub-order Usterts.

2.8.2.4 Red Sandy Soils

These soils occur on undulating landscape on acidic rock viz. Granites and granite

gneisses, occupying areas in parts of Dharwad, Bellary, Chitradurga, Shimoga,

Bangalore, Tumkur, Mandya and Mysore districts of the State.

The soils of this type can further be sub-divided into the following three groups

occupying on distinct topographic sites with varying physicochemical properties. a)

Upland, b) Midland and c) Low land soils.

The soils are shallow to moderately deep, reddish brown to dark reddish brown,

gravelly loamy sand to sandy loam on the surface with sandy loam to gravelly sand

clay in the sub-surface horizons. They are neutral to slightly acidic in reaction and

low in cation exchange capacity, base saturation and water holding capacity but well

drained with rapid permeability. These soils are classified under the orders Entisols,

Inceptisols and Alfisols with sub-orders, Orthents, Ochrepts and Ustalfs.

2.8.2.5 Mixed Red and Black Soils

These soils usually occur on gently undulating plain or complex geological material

comprising of gneisses. This type of soil occupies areas in parts of Bijapur, Dharwad,

Belgaum, Raichur, Bellary and Chitradurga districts.

58

Usually red soils resemble the red sandy soils of midland region in physic-chemical

properties and black soils resemble the medium and deep black soils in physic-

chemical characteristics. These soils are classified under the orders Alfisols, Vertisols

and Entisols with sub-orders Ustalfs, Usterts and Orthents.

2.8.2.6 Red Loamy Soils

These soils occur on hilly to undulating landscape on granites, granitic gneisses and

Dharwad schists, occupying areas as a long strip along the western ghats in the

transitional zone comprising western parts of Belgaum, Uttara Kannada, Shimoga,

Chitradurga, Udupi, Mangalore, Hassan and Kodagu districts and parts of

Chitradurga, Tumkur, Kolar and Bangalore districts.

The soils of this region can further be sub-divided into the following three groups

occurring on distinct physiographic position and have varying physico-chemical

properties; a) Upper slops, b) Undulating mid-slopes and c) Valley plain soils. These

soils are classified under the orders Alfisols and Entisols with sub-orders Ustalfs,

Udalfs and Fluvents.

2.8.2.7 Laterite Soils

These soils mainly occur on gently undulating, rolling, plain to hilly topography of

Peninsular gneiss and the Dharwad schist regions, occupying areas as a long strip,

along with the western coast in the coastal high rainfall and transitional region

comprising major parts of the districts of Uttara Kannada, Udupi, Mangalore, Kodagu

and Western parts of Hassan, Chikkamagalur, Shimoga, Dharwad and Belgaum

districts; also found in parts of Bangalore, Kolar, Bidar and Gulbarga districts.

These are deep to very deep, yellowish red to dark red, reddish brown to brown, clay

loam to gravelly sandy loam on the surface and clay loam to gravelly sandy clay or

clay in the sub-surface horizon. These are well drained to excessively drain with

moderate to moderately rapid permeability. These soils are classified under the orders

Entisols, Ultisols, Alfisols and Oxisols with sub-orders Orthents, Ustults, Udults,

Ustalfs, Udalfs and Ustox.

59

2.8.2.8 Laterite Gravelly Soils

These soils occur in patches especially on the convex upland region of the laterite i.e.,

in the southern parts of the districts of Udupi and Mangalore, northern parts of

Shimoga and north-eastern parts of Bangalore districts. Other characteristics are

similar to laterite soils described above. These soils are shallow to moderately deep

with abundant ferruginous gravels.

2.8.2.9 Coastal Alluvial Soils

These soils occur on gently sloping to nearly level plains as a narrow strip along the

western coast in the districts of Uttara Kannada, Udupi and Mangalore. They are

deposited soils consisting of washed down materials from the Western Ghats and by

the action of the Arabian Sea.

These are deep to very deep, light grey, pale yellow or brown, sand loamy sand to

sandy loam on the surface, with loamy sand, gravelly sandy loam to clay loam in the

sub-surface horizons. These are acidic in reaction, low in CEC base saturation and

water holding capacity and deficient in the major nutrients. The water table in the low

lying areas is usually within 1.0 to 1.5 metres for most parts of the year. These soils

are classified under order Entisols with suborders Aquents, Fluvents and Psamments.

60

Figure- 2.7: Major soil order of Karnataka.

61

Figure- 2.8: Different soil groups of Karnataka state (National Bureau of Soil Survey

(NBSS) and Land Use Planning (LUP), Nagpur).

62

Table – 2.2: The soil type of Karnataka state.

Soil

units

Description Physiography Districts Area

(ha) -

%

Red

soils

Red

gravelly

loam

soils

Shallow well drained to

excessive ly drained, reddish

brown to Yellowish brown,

gravely sandy loam to sandy

clay loam, moderate to

severely eroded.

Hills and ridges,

rolling and un-

dulating lands of

plateau and Eastern

Ghats.

Bangalore, Belgaum,

Chikma galur, Kolar,

Mysore, Raichur and

Tumkur

31599

4

1.66

Red

loam

Soils

shallow, excessively drained

to well drained, reddish

brown to yellowish red,

sandy clay loam to sandy

loam soils, oderately to

severely eroded.

Ridges, rolling and

undulating lands of

plateau

Bangalore, Bellary,

Belgaum, Bijapur,

Dharwad, Mysore,

Gulbarga and Raichur

19104

1

1.00

Red

gravely

clay

soils

Deep to mod. deep and

shallow, well drained to

excessively drained,

yellowish brown dark red to

reddish brown, gravely

sandy loam to sandy clay

loam and loamy sand

surface soils and gravely

sandy clay to clay sub

surface soils, moderately

toSeverely eroded.

Hills and ridges,

hillranges, rolling

gently and

ndulating lands,

inter-hill basins of

plateau, western

Ghats,Weastern

Ghats

Bangalore, Bellary,

Belgaum, Bijapur,

Chikmagalur,

D.Kannada,

U.Kannada, Mysore,

Kolar, Kodagu, Hassan

and Mandya

36109

76

18.95

Red

clay

soils

Deep to mod. deep and

hallow, well drained, brown

to yellowish red to reddish

brown, sandy loam and

sandy clay to clay

subsurface soils, oderately to

severely eroded.

Hills and ridges,

high hill ranges,

rolling, undulating

and gently sloping

lands of plateau

western and

Wastern Ghats

Bangalore, Bellary,

Belgaum, Chitradurga,

D.Kannada, Dharwar,

Gulbarga, Hassan,

Kodagu, Kolar,

MandyaRaichur,

Shimoga Tumkur, and

U.Kannada

29903

73

15.69

Laterite

soils:

Laterite

gravely

Deep, well drained to

excessively drained,

yellowish red to dark

reddish brown, gravely,

Mounds summits

and upper slopes of

Plateau, sloping

Lands of malnad.

Bangalore, Belgaum,

Bidar, .Kannada,

.Kannada, Gulbarga,

Kodagu, Kolar,

51159

3

2.74

63

soils sandy clay and clay surface

soils moderately to everely

eroded with surface crusting.

Shimoga and Dharwar

Lateritic

soils

Deep, well drained to

excessively drained,

yellowish red to reddish

brown, sandy loam to sandy

clay and clay surface soils

and clay subsoils, moderate

ly to severely eroded with

Surface crusting

Gently sloping

Plains, Summits of

plateau, Steeply

sloping lands of

Western Ghats and

Malnad

Bangalore,

Chikmagalur,

D.Kannada, Hassan,

Kodagu, Kolar,

Mysore, Shimoga and

U. Kannada

65344

0

3.42

Black

soils:

Deep

black

soils

Deep, moderately well

drained, Dark greyish brown

to very dark greyish brown,

calcareous cracking clay to

silty clay soils moderately to

severely eroded

Gently sloping

Plains, plateau

summits, valleys

Bellary, Belgaum,

Bidar, Bijapur,

Chitradurga, Dharwar,

Gulbarga, Mysore and

Raichur

31087

04

16.32

Medium

deep

black

soil

Moderately deep,

moderately well drained,

dark brown to very dark

greyish brownmoderately to

severely eroded

Gently sloping

lands and plains,

summits of plateau,

valleys

Bellary, Belgaum,

Bidar, Bijapur,

Chitradurga, Dharwar,

Gulbarga, Hassan,

Raichur, Shimoga,

Tumkur, Bidar,Bijapur

59837

6

3.13

Shallow

black

soils

Shallow, well-drained grey

to dark grey and brown clay

loam to silty clay loam soils,

severely eroded.

Plateau summits

and table lands

Belgaum, Bidar

Gulbarga and Bijapur

15860

70

8.32

Alluvio-

colluvial

soils:

Non-

saline

Deep to shallow, oderately

well-drained to imperfectly

drained and poorly drained,

yellowish brown to strong

and dark greyish brown non

saline, clay loam to clay and

andy clay loam surface soils

and clay to clay loam and

sandy clay loam, subsurface

soils

valleys, low lands

of plateau and

Malnad

Bangalore, Belgaum,

Bijapur, Chikmagalur,

Dharwar, Gulbarga,

Kodagu, Kolar and

Shimoga

36147

1

1.90

Saline

and

sodic in

Deep, moderately well-

drained to perfectly drained,

dark greyish brown and

Valleys, lowlands

very gently sloping

plains of command

Bangalore, Bellary,

Bidar, Bijapur,

Chikmagalur,

26362

33

13.64

64

patches strong brown, clay to sandy

clay and clay loam surface

soils and clay to loam

subsurface soils with salinity

and alkalinity in patches

areas of Plateau Chitradurga, Dharwar,

Hassan, Kolar,

Mandya, Mysore,

Raichur, Shimoga and

Tumkur

Forest

soils

Brown

forestsoi

l

Deep to mod. deep, well

drained to excessively

rained, dark brown to dark

yellowish brown and black

sandy clay to sandy clay

loam, humus rich surface

soils and clay to sandy clay

subsurface soils, slightly

eroded.

Hill ranges and

steeply sloping

lands of Western

Ghats

Belgaum,

Chikmagalur,

D.Kannada, Dharwar,

Hassan, Kodagu,

Mysore, Shimoga and

U. Kannada

11473

27

6.00

Coastal

soils:

Coastal

laterite

soil

Deep, well drained to

excessively drained, dark

brown to yellowish red and

dark reddish brown sandy

clay loam to clay loam

surface soils and sandy clay

to clay subsurface soils,

moderately to severely

eroded with surface crusting.

coastal uplands, and

hinter lands

D.Kannada,

U.Kannada

56325

4

2.96

Coastal

alluvial

soils

Deep, well-drained and

poorly drained, pale brown

to dark yellowish brown,

sand, sandy loam to loam

surface soils and sand to

loam subsurface soils.

Bars, beaches,

beach ridges,

valleys

D.Kannada,

U.Kannada

18026

7

0.94

2.8.3 Soil depth of Study Area

Depth of the soil determines the effective rooting depth for plants and in accordance

with texture, mineral and gravel content, the capacity of the soil column to hold water.

To classify the soil map units into depth classes, some generalisation in respect of

depth classes has been made as large numbers of combinations occur. Accordingly,

six depth classes have been made and the extent of area under each class has been

given below (Table- 2.3, Figure- 2.9).

65

Table- 2.3: Soil depth classes of Karnataka state.

Class Depth

(cm)

Area

‘000 ha. (%)

Extremely shallow 00 - 10 76.3 0.4

Very Shallow 10 - 25 2547.9 13.4

Shallow 25 - 50 497.8 2.6

Moderately shallow 50 -75 1706.4 9.0

Moderately deep 75 - 100 2717.1 14.3

Deep >100 10907.7 57.3

Figure- 2.9: Soil depth maps of study area (National Bureau of Soil Survey (NBSS)

and Land Use Planning (LUP), Nagpur)

66

2.8.4 Soil types of Study Area.

The soil type around Mysore is grouped broadly into three main types viz.,

1. Red sandy soils

2. Red loamy soils

3. Deep black soils

However, soil map prepared by geological survey of India gives a detailed

classification of different types of soils around Mysore (Figure- 2.10). Out of

different soil-types, for the present study the following 5 types of soils has

been selected:

9 =Very Deep, Gravely Clay Soil

11= Moderately Shallow, Gravely Clay Soil

53 =Very Deep, calcareous Clayey soil

58= Very deep, Gravely Loam soil

76 =Shallow Gravely Clay Soil with Rock Land

A comparison of five different types of soils with the geology around

Mysore in the Dharwar Craton , indicate that different types of soils present in

the Mysore region is controlled by different types of rocks. The general

elevation of the area ranges between 700 to 900 meters with an average rain

fall between 600 to 900 mm. Presence of different types of soils exposed

around Mysore , with similar topographic and rain fall conditions strongly

suggest the influence of rock types which control the soil formation.

67

Figure- 2.10: Soil types of study area along with sample locations (National Bureau of

Soil Survey (NBSS) and Land Use Planning (LUP), Nagpur).