CERTIFICATE

Certified that the project titled “ Petrological

Studies Of Sedimentary Formations at Bilgi,

Bagalkot District, Karnataka” is the record of the

work done under my guidance by the candidates

themselves during the year 2013-2014, and that to

the best of my knowledge it has not previously

formed the basis for the award of any degree or

diploma in Goa University or elsewhere.

Shri. H. S. S. Nadkarni

Shri. H. S. S. Nadkarni HOD, Dept. of Geology

SUPERVISOR/GUIDE

Date: 28th February

COURSE: B.Sc. (GEOLOGY)

YEAR: 2013-2014

PARVATIBAI CHOWGULE COLLEGE, MARGAO-GOA

DECLARATION

We declare that this project report has been

completed by us and it has not previously formed

the basis for the award of any diploma or other

similar titles.

CLASS: T.Y.B.Sc

SUBJECT: GEOLOGY

2

Roll No. Name Signature

110709663 Carvalho Dylan R.

110703701 Gois Johnathan

110709620 Fernandes Revellino A.

110709586 Rodrigues Dryden J.

110709704 Farhan Shaikh

ACKNOWLEDGEMENT

We express our sincere gratitude to our field

guide and HOD, Dept. of geology, Shri. H. S. S.

Nadkarni for his guidance, motivation and in

inspiring us to complete this project.

We are thankful to Ms. Meghana S. Devli for her

timely advice and support.

3

We also express our gratitude to Shri. M. S. Katti

and Shri. Allan Rodrigues for their encouragement.

A special thanks to our laboratory assistants Mrs.

Sangeeta Virdiker and Shri. Shalil Naik for

providing the necessary arrangements.

Lastly we would like to express our deep gratitude

to our parents for their support and blessings in

the completion of this project.

CONTENTS CHAPTER 1 Page No

4

1.1 Physiography of Bagalkot District

9

1.1.1 Location and Topography

9

1.1.2 Drainage

10

1.2 Geology and Distribution of Kaladgi

Basin 11-12

1.2.1 Lithostratigraphy of

Kaladgi Super-group 13-14

1.2.2 The Bagalkot Group

15

1.2.3 The Badami Group

15

5

1.2.4 Biota and Time Connotation

16 1.2.5 Formation of the Kaladgi-

Badami basin 17 1.2.6 Sedimentary Structures

18

1.2.7 Paleocurrent studies

19

1.2.8 Depositional environment and

Metamorphism 20

1.2.9 Economic Importance

21

CHAPTER 2

6

METHODOLOGY

22

2.1 Location/Topography of study Area and

Objectives 23

2.2 Field Work

24- 26

2.3 Laboratory Data

27 2.3.1 Megascopic Identification of

Rock Samples 27- 29

2.3.2 Microscopic Identification of

Rock Slides 30- 38

7

CHAPTER 3

DISCUSSION OF VARIOUS TOPICS

3.1 Paleocurrent Analysis

39

3.2 Identification of Pellitic and Prismatic

crystals found in thin section of Conglomerate

40-41

3.3 Distinction between Bagalkot quartzitic sandstones and Badami arenites

42

3.4 Occurrence of pyrite and xenoliths in

granite 43

3.5 Stratigraphic sequence

44

8

CHAPTER 4

4.1 Conclusion

45

BIBLIOGRAPHY

9

CHAPTER 1

INTRODUCTION

Among 19 districts of Karnataka the district

of Bagalkot is situated towards the North of

the state. Bāgalkot district is an

administrative district in the Indian state

10

of Karnataka. The district headquarters is

located in the town of Bagalkote.

The district is located in northern

Karnataka and

borders Belgaum, Gadag, Koppal, Raichur and 

Bijapur.

Ghataprabha River, Malaprabha

River and Krishna River flow through the

district. Koodalasangama lies at the point

of confluence of rivers Krishna and

Malaprabha.

11

1.1 PHYSIOGRAPHY OF BAGALKOT DISTRICT

1.1.1 LOCATION AND TOPOGRAPHY

Bagalkot district is located in the northern

part of the state of Karnataka. Bagalkote

district is bound by Bijapur in the north,

Belgaum in the west, Dharwar in the south

and Raichur in the east. The district

comprising of 6 taluks, occupies an area of

6593 sq.kms (constituting around 3.4 percent

of the area of the state) and lies between

15° 49’ & 16° 46’ north latitude and 74° 58’

& 76° 20’ east longitude.

The area is a gently undulating to a plain

terrain, dotted with isolated hills. The

elevation ranges from 480 to 729 metres

amsl, sloping from west to east. The

district falls in the Northern dry Agro-

climatic zone and experiences a semi-arid

12

climate. It is one of the drought -prone

districts of the State.

1.1.2 DRAINAGE

The district is drained by the river Krishna

and its tributaries Ghatprabha and

Malaprabha. All these rivers enter district

on the western side and flow in an easterly

direction to join the Bay of Bengal. Krishna

River enters the district at Terdal village

in Jamkhandi taluk and flows in south-

easterly direction and forms the northern

13

boundary of the district separating it from

Bijapur district. The Ghataprabha River

flows in the middle part of the district and

joins the Krishna in Chikkasangama village

in Bilgi taluk. The Malaprabha flowing in

the southern part, joins the Krishna at

Kudal Sangama in Hungund Taluk. The

Ghataprabha and Malaprabha canal systems

serve the western parts of the district. The

Dam across the Krishna river at Almatti and

the canal systems serve the eastern parts.

Rainfall being as low as 560 mm annually,

these canals are the lifelines, providing

much needed irrigation and drinking water to

the district.

14

1.2 GEOLOGY AND DISTRIBUTION OF KALADGI

BASIN

It is said that towards the end of the

Archaean prolonged changes occurred in the

middle Proterozoic creating large

sedimentary basins at the margins and

interior parts of the craton.

There are no sedimentary sequences belonging

to the early Proterozoic in the Dharwar

craton. Sediments middle Proterozoic age got

deposited and eroded the upturned edges of

the older rocks like schists, gneisses and

granites of Archaean age.

Evidence of life is based on occurrences of

‘stromatolites.’

15

By the end of the Archaean Era has formed

the bulk of the continental crust. The Basin consists of a thick sequence of

sediments occupying parts of Bijapur,

Belgaum, Bagalkot, Dharwar and Raichur

Districts of Karnataka and form one of the

most distinct and interesting Proterozoic

suite of rocks in peninsular India.

These rocks occupy the E-W trending basin

stretching nearly 500kms and covering about

8000 sq. km overlying peninsular gneissic

complex of the Archaean age and underlying

the Deccan traps of the Cretaceous- Eocene

age. The rocks were first noted in Kaladgi

town in Bagalkot districts therefore are

known as the ‘Kaladgi Supergroup’.

The rocks of this group extend into Kolhapur

and Sangli districts of Maharashtra and are

partly concealed by the Deccan traps to the

16

north and present disposition is irregular

due to extensive overlapping lava flows.

Outcrops are seen at different places one of

them at Jamkhandi in the north as inliers in

Deccan traps, the outcrop limits to the east

are at Niogundi with the lokapur subgroup

forming a synclinal closure. At Gajendragad

and Hanumasagar the Badami Arenites occur as

outliers on the Granitoids. The basin

extends in the west up till Mahagoan in

Kolhapur district of Maharashtra.

17

1.2.1 Lithostratigraphy of the Kaladgi-Badami Basin

Group Subgroup Formation

Member Thickness

BadamiGroup

Katageri Konkankoppa limestone 85mHalkurki shale 67m

KerurBelikhindi arenite 39mHalgeri shale 3mCave-temple arenite 89mKendur conglomerate 3m

-------------------------Angular unconformity---------------------------

Bagalkot Group

SimikeriSubgroup

Hoskatti Mallapur intrusive 7mDadanhatti argillite 695m

Arlikatti

Lakshnhatti dolomite 87mKerkalmatti haematite schist

42m

Niralkeri chert-breccia

39m

Kundargi Govindkoppa argillite

80m

Muchkundi quartzite 182mBevinmatti conglomerate

15m

-----------------------------Disconformity------------------------

18

Yadhalli Argillite 58m

LokapurSubgroup

Muddapur Bamanbudni dolomite 402mPetlur limestone 121mJalikatti argillite 43m

Yendigeri

Naganur dolomite 93mChilksheri limestoneHebbal argillite 166m

Yargatti Chitrabhanukot dolomite

218m

Muttalgeri argillite 502mMahakut chert-breccia

133m

Ramdurg Manoli argillite 61mSaundatti quartzite 383mSalgundi conglomerate

31m

------------------------Nonconformity----------------------------

Granitoids, Gneisses and Meta-sedimentsThe Kaladgi Supergroup overlies peninsular

gneissic complex and is sub-divided into two

groups namely Lower Bagalkot group and upper

Badami group. The basin has an average

thickness of about 4500m. Four facies

represent this basin

1. Sandstone facies: consist of mainly

quartzites, sandstones and arenites and

19

classed as quartz arenites and quartzite

wackes.

2. Argillite facies: includes siltstones

and shales, brown to purple coloured.

3. Chert-Breccia facies: it is an

interesting rock composed of pink

cryptocrystalline silica in which

angular fragments of chert are embedded.

Breccias contain pyroclastics.

4. Carbonate facies: Extensive beds of

dolomites and limestones.

a. Dolomites: are differently colored

being bluish to greenish grey to black.

Bands of stromatolites structures are

abundant said to be of secondary

origin.

b. Limestones: are thickly bedded

deposits and occupy low grounds covered

by black soil.

5. Intrusive Igneous Rocks: exist as few

minor dykes.

20

1.2.2 THE BAGALKOT GROUP

Are the older Kaladgis, which are further

divided into two subgroups namely, the

Lokapur group and the Simikeri group. These

are inclined beds. Lokapur consists of five

formations and 13 members and Simikeri

consists of 3 members and 8 members. This

subgroup has a larger aerial spread and has

a huge cumulative thickness of four times

the Simikeri group.

1.2.3 THE BADAMI GROUP

These rocks are horizontally deposited and

overlie the Bagalkot series of rocks as well

21

as Granitoids in places with a distinct

unconformity marked by a presence of a

conglomerate. This succession includes two

formations Kerur and Katgeri formations and

consists of 6 members.

1.2.4 BIOTA AND TIME CONNOTATION

Microfossils of algal spaeromorphs,

acritarchs and cellular tissues with organic

debris are found in the rocks of the lokapur

Subgroup. Venkatachala based on palyno-

assemblage allotted a time age of

Precambrian to the subgroup. In badami group

22

of rocks, visvanathiah, recorded acritarcha

belonging to deseonochitina , cyathochitina,

conochitina, acantichititna, on as is was

suggested that it belonged to the Ordovician

age. Also microbiological studies suggest

that the lokapur subgroup was attributed to

the middle-upper Riphean to Vendian ( lower

Cambrian age).

Raha et al said that the bagalkot group was

of the middle Riphean age belonging to the

Nallamalai group (Cuddapah system).

Siliceous stromatolites confirm the age of

the assemblage as of the middle Riphean age.

About 1,260 – 1,000 million years.

It is concluded that these subgroups are

similar to the Cuddapah and the Vindhyan

systems and the entire sequence of rocks may

be in the range of Neo-proterozoic to

Eocambrian age.

23

1.2.5 FORMATION OF THE KALADGI-BADAMI BASIN

Granitoids and meta-sediments are the oldest

rocks recorded. These were cut down to base

level by erosion after a long time a thick

layer of Kaladgi sediments was deposited in

a shallow platformal basin.

Pulsating conditions of the basin are noted

by the cyclic nature of sediments. Each

cycle starting within the clastics and

ending with the chemical precipitates.

Disconformity between the lokapur and

Simikeri subgroups suggests a period of no

erosion as shown by a basal conglomerate

present there.

After deposition of the bagalkot group the

sea retreated followed by uplift and

24

tectonism with compressional forces mainly

acting NNE-SSW axis throwing the sediments

into anticlines and synclines with their

axis trending WNW-ESE. After this a new set

of sediments were deposited called as the

Badami group of sediment. A few hundred

million years later the region received

another layer of rocks namely basaltic lavas

of Deccan in the form of fissure eruption

interlayers with predominantly lacustrine

inter-trappean sediments.

Sedimentation is said to have occurred as a

result of two megacyclothems and a major

hiatus in between. Megacyclothem of the

bagalkot group consists of 2 macrocyclothems

viz. lokapur and Simikeri with a

disconformity representing uplift and

denudation, these consist of meso-cycles

represented by a term. Lower terms consist

of coarse and fine-grained clastics; rests

25

are argillites alternating with chemical

precipitates like limestone etc.

Megacyclothem of the Simikeri subgroup has 3

terms having numerous micro-cycles. Micro-

cycles are attributed to climatic variation

while megacycles and mesocycles are result

of tectonic activities, provenance and

eustatic changes.

1.2.6 SEDIMENTARY STRUCTURES

Graded bedding, cross- bedding is present in

almost all arenites and quartzites, thickly

or thinly laminated at places. All shales

are finely laminated with prominent bedding

plane. Limestones and dolomites are medium

to thickly bedded sometimes, showing fine

laminated bedding. Groove casts, parting

lineation, ripple marks are common in cave-

temple arenite.

26

Sediments of the lokapur subgroup display

doubly plunging synclinal structure formed

as a result of faulting and folding.

Warpings are also seen in Yargatti, Katageri

and Sirur formations.

1.2.7 PALEOCURRENT STUDIES

Paleocurrent studies were undertaken on the

all the sedimentary structures predominantly

the Badami arenites and the saundatti

quartzites on a lesser scale, two areas are

identified for study one is the Badami type

area and the other is the Anwal sampling of

saundatti quartzite, and the azimuth of the

resultant vector, found by drawing 1×1.5km

grids.

27

Azimuth of the vector ranges from 160 – 282

degrees therefore the current moved from NE

to SW.

1.2.8 DEPOSITIONAL ENVIRONMENT AND METAMORPHISM

28

Depositional environments were studied using

sedimentary structures and textures

available. Discontinuous thin shale partings

are generally seen in all the dolomites with

irregular bedding this is a diagnostic

property of Supra-tidal sedimentation.

Presence of stromatolites, algal mats and

intraformational conglomerates/breccias are

suggestive of tidal environment.

Wavy bedding and convolute laminations in

quartzite and arenites are the other

evidences of deposition in intertidal seas.

there is also evidence of High velocity

shallow water environment as suggested by

mega trough cross beds.

therefore concluded that the sediments of

Kaladgi Supergroup were predominantly

deposited under tidal and beach environment.

Effect of metamorphism on Badami groups is

almost nil, but the rocks of bagalkot group

show noticeable metamorphism. Major portion

29

of arenite beds of Bagalkot group have

altered to quartzites as a result of low-

grade metamorphism. Shales were subjected to

compression with reduction of porosity and

ultimately alteration to argillites.

1.2.9 ECONOMIC IMPORTANCE

Limestones are the greatest assets in terms of

mineral potential of the Kaladgi Supergroup.

Material estimated is of many grades.

Other materials of importance are the Haematite

schists of Simikeri subgroup with max thickness

of about 50m resources computed to about 10

million tons of oxidized iron ore.

30

Raw material of commercial importance and

abundance are dolomite quartzite and novaculite

and argillites.

Cave temple arenites are used for ornamental

stone, building material, etc.

CHAPTER 2

METHODOLOGY

31

2.1 Location & Topography of Study Area and Our Objectives

An elongated ridge exposes the various

formations of this place and as the approach is

easy the outcrops are easily accessible. Having

previously visited the area under study at

Bilgi during the field tour we decided to

undertake a detailed study for the lithological

units in the region, and try to understand the

geology.

The town of Bilgi is located at 16°20′50″N

075°37′05″E. It has an average elevation of

509 metres (1669 feet). Toposheet No.

The taluka covers 782 square kilometres

(301.9 sq mi) and lies between 16°-03′ to 16°-

32′ north latitude and 75°-73′ to 76°-49′ east

longitude. The taluka is bordered by Bijapur

Taluka of Bijapur District to the north, Mudhol

Taluka to the west, Bagalkot Taluka to the

south and southeast, and Jamakhandi Taluka to

32

the north. The Krishna River and reservoir form

its northern boundary.

The region is hilly and sparsely vegetated with

thorny shrubs indicating semi-arid climate. The

jointing pattern in the rocks have supported

the vegetation to some extent the hill range

have a maximum elevation of more than 600

meters above mean sea level and show steep

escarpment slope on one side while the other

exhibits are dip slope. This pattern is very

distinctive forming narrow v-shaped valleys

between 2 hills. The drainage occupies the

valleys.

Though our knowledge of geology is restricted

we tried to make a fair attempt in achieving

our objectives.

Our objectives,

1) Collection of samples

2) Making field observations

33

3) Constructing the

stratigraphic/lithological column of

different litho-units.

As the approach to the ridge is through the

village, we chose our 1st spot at its base on

the southern side.

2.2 FIELD WORK

34

Traverse 1

A traverse was carried out from the base of the

hill constituting one section of the ridge to

the top. Granites were exposed at the base of

the ridge. They were exposed as ‘Tors’.

The granitic body showed sheet jointing as

such, formed from the effect of stress and

temperature. These granites were composed of

essential minerals, orthoclase feldspar and

smoky quartz, pink quartz transparent quartz.

Accessories include Pyrite.

Dark Black colored Xenoliths having texture to

that of charred coal have been noticed and

these xenoliths are probably thought to have

been caught up in the granitic magma during its

intrusion.

Also seen intruding the granite are Orthoclase

veins having thickness from 5- 13 cm.

35

As we walked about 10 – 15m directly above the

granitic intrusions we encountered brecciated

rocks. These breccias were indicative of Shear

zone between the granitic plutons and the

Kaladgis, which we like to call an

unconformity. The breccias comprise of

Orthoclase & Microcline feldspar and Quartz.

Since it is a shear zone coarse-grained

breccias were found at a higher elevation

compared to the fine-grained breccias found at

the lower elevation.

After which we moved S 36°W we encountered

Quartzitic sandstones of the lower Kaladgis.

The first beds we came across were of highly

ferruginous nature and showed 3 sets of joints,

the first was the bedding, second was trending

N 308° and the third was trending N 195°.

Thickness was approx. 0.5m.

Traversing a little higher from the previous

spot, the quartzitic bed showed a compositional

36

variation from being siliceous initially to

being ferruginous later.

The quartzitic sandstone strikes along S60ᴼE

dipping by an amount of 10ᴼ towards S30ᴼW and

has thickness of about 38-65cm, which was also

jointed with the same trend as above, on moving

up we came across the contact of a ferruginous

quartzitic sandstone with thickness about 1m.

The sandstone showed incrustations of iron

oxide due to deposition occurring along joints

by ferruginous solutions.

The quartzitic sandstones show cross-bedding

trending S 45°W and ferruginous beds show pink

colors due to leaching of iron.

37

Traverse 2

The ridge was weathered resulting formation of

a small valley through which a dolerite dyke

had intruded. This dyke was further lateritized

due to soggy conditions.

Overlying the intrusion, bands of siliceous and

ferruginous quartzitic sandstones were of much

more greater thickness than observed before.

The siliceous bands had thickness of about 2m

and the ferruginous beds had a thickness of 1.1

– 2.85m. Traversing a little higher jointing

was seen and were inclined and trending N 60°W.

The sandstones mainly comprised of bands that

were more ferruginous and less siliceous. They

were cross-bedded and showed dendritic patterns

occurring due to leaching of minerals.

Traverse 3

38

At the base we encountered an exposure of

granite that was weathered to clay. It showed

foliation and sheet jointing proving it was

gneissic granite. Traversing about 15- 20m

higher we came across a bed of Graded

conglomerate the exposure indicated a break in

the deposition. This is an angular unconformity

between the younger Badamis and the older

bagalkot rocks i.e. the Kaladgi basins. The

longest axis of 50-60 pebbles in the

conglomerate was measured and the average value

was found to be 5.52cms and trending S 80°W.

Orientations of pebbles can help us in

understanding Paleocurrents of the region.

2.3 LABORATORY DATA

2.3.1 MEGASCOPIC IDENTIFICATION OF ROCK SAMPLES

1. GRANITE

39

The rock is porphyritic holocrystalline and

inequigranular. The colour index is

leucocratic. The composition of the rock is

quartz, orthoclase which occurs as phenocrysts

as well as in medium grained groundmass and

Pyrite occurs as accessory mineral, shows,

distintive metallic lustre and gold like

appearance. Quartz is identified by its

vitreous lustre and white colour, Pink quartz

and smoky quartz are seen abundanty. Orthoclase

is reddish- pink with 2 sets of cleavage Small

greenish-black crystals of hornblende can also

be identified based on their prismatic habit.

It shows no visible structure. Also seen are

dark colored xenoliths of the older

metasedimentaries.

On the basis of the above observations, the

rock is classified as plutonic acid igneous

rock named granite.

40

2. BRECCIA

The rock shows a clastic texture.Grain size is

Medium-large.Grains are angular in shape. The

rock is coarsely grained. The rock is composed

of Smoky/Milky/ quartz and Red Orthoclase

feldspar.The cementing material is siliceous.

The quartz can be identified by its milky white

colour and orthoclase is identified by its sub-

vitreous lustre ,pinkish red colour and

cleavage.The grains are cemented in a siliceous

matrix. It is found along the contact of the

Granite and the Kaladgis which has to make it a

conglomerate or breccia. But, on the basis of

the above observations, the rock is classified

as mechinally formed rudaeceous sedimentary

rock named breccia.

3. CONGLOMERATE

41

The rock is constituted of rounded to sub-

rounded cobble/pebble sized clasts of quartz

embedded in a siliceous matriz. It is coarse-

grained. Long axis of the pebbles measure about

5.42cm. The pebbles are well rounded. The

matrix also accompanies angular clasts of pink

coloured orthoclase feldspar besides quartz. It

also contains fragments of Red Jasper

occasionally It is thoroughly indurated and can

be classified as Rudaeceous Polymictic

conglomerate.

4. SILICEOUS QUARTZITES

The rock shows a granoblastic texture with a

compact fusion of quartz grains. It is greyish

with a vitreous lustre and is entirely

siliceous in nature. The effect of low grade

42

thermal metamorphism is thus evident that the

parent rock is sandstone.

5. FERRUGINOUS QUARTZITES

The rock is pinkish in colour indicating its

ferruginous nature. The quartz grains showing

vitreous lustre are compactly fused under the

effect of low grade thermal metamorphism. It

saccharoidal nature classifies the rock as a

quartzite that has been derived from its

sandstone protolith.

6. ARENITE

The specimen of the rock exposed at the outcrop

is seen to prominantly possess irregular grains

of quartz and pink colored orthoclase feldspar,

both these have lost their lustre and have

become dull. They are haphazardly cemented in

the siliceous matrix. The rock is coarse-

grained and has a clastic texture. As both

43

quartz and feldspar are seen in equal measures

the specimen could be termed as an Arenite.

2.3.2 MICROSCOPIC IDENTIFICATION OF ROCK SLIDES

1) Slide 1 (BIL-4)

Ferruginous Quartzitic Sandstone.

Texture: - Clastic

o Grains have point contacts.

o Grains are sutured, single grains

floating in matrix are found.

o Overall grains occupy more area than

the matrix.

o Quartz grains show cracking due to

stressing conditions.

Formation: Mechanical/Chemical

Classification: Arenaceous

44

Composition: Quartz, Feldspar,

Possible muscovite mica and mafic

bodies; matrix is ferruginous,

siliceous and argillaceous.

Anisotropic Character:

o Extinction after 90ᴼ Rotation –

Straight Extinction

o Grey of 1st order→ confirms Quartz.

o Grains, sometimes, contain small

grains, which shows straight

extinction, 3rd order greens, etc.

which could be muscovite micas.

o Dark grains found representing

opaques.

o Matrix is isotropic containing Fe and

is of a brownish/orangish tinge.

o Clay is seen in the matrix, which has

come from the alteration of

feldspars, hence, feldspars are

present.

o A grain is seen to have undulose

extinction which says that strain

45

build up within the crystal lattice

causing it to warp. Therefore

different parts of the crystal go

into extinction at different angles

giving the crystal a mottled look.

Leaching and precipitation of iron has lead to

formation of a ferruginous matrix.

46

2) Slide 2 (BIL- 6)

Breccia

Texture: - Clastic, Grain size is

large, Grains are angular in shape and

have point contacts with little or more

matrix the rock has a clast-supported

framework.

Classification: - Rudaceous

Formation: Mechanically formed; void

spaces filled with alteration product

of feldspars i.e. clay

Composition:

o Quartz

o Microcline feldspar

o Orthoclase feldspar

o Slightly Ferruginous matrix but

mostly siliceous

o Muscovite mica

Anisotropic Character:

47

o Grains go into extinction after

90ᴼ rotation- Straight Extinction

o Interference colors seen, mostly,

Grey of 1st order and some 3rd

order interference is seen in

smaller grains.

o 3rd order interference is shown by

muscovite mica formed by,

“sericitization”.

o Grains are highly cracked and

fractured thereby indicating a

high degree of stress

o Quartz shows interference color

grey of 1st order

o Microcline shows characteristic

‘tartan twinning’

o Orthoclase shows characteristic

‘lamellar twinning’, tabular, 2

sets of cleavage.

48

3) Slide 3 (BIL -9)

Ferruginous Quartzite

Texture:

o Clastic,

49

o Well sorted, grain size is medium,

grains are angular in shape to

rounded,

o Grains have point contacts and/or

seen to float in the matrix,

o In some places some grains are

sutured.

o Cementing matrix is filled in

between grain spaces.

o Some grains are highly fractured

and cracked indicating stress.

Formation:

o Mechanical/ Chemical

o Oxidation of iron ore leading to a

highly ferruginous matrix (Red in

color)

Classification:

o Arenaceous

Composition:

o Clasts: Quartz, few grains of

orthoclase feldspar

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o Matrix: mostly ferruginous and less

siliceous and slightly argillaceous

Anisotropic Character

o Extinction after 90º Rotation-

Straight Extinction

o Grains show interference color grey

of 1st order

o No alteration products seen

Leaching of Iron has Occurred and

Accumulated in quartzite in its matrix.

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4) Slide 4 (BIL-1)

Siliceous Quartzitic Sandstone

Texture:

o Clastic, grain size is medium

o Grains are sub-rounded to angular,

o Grains have point contacts,

sometimes floating and some covered

by siliceous matrix

o Cementing matrix fills gaps between

grains

o Some grains are cracked indicating

stress

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Formation: Mechanical

Classification: Arenaceous

Composition:

o Clasts: mostly Quartz and traces of

feldspar

o Matrix: Siliceous and Colorless

made up of SiO2 also is slightly

ferruginous and argillaceous

Anisotropic Character:

o Extinction- Straight i.e. 90º

rotation

o Interference: 1) Clasts: Grey of 1st

order

2) Matrix:

Isotropic

No Alteration is seen.

5) Slide 5 (BIL- 13)

Conglomerate

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Texture:

o Clastic, grain size is large

o Grains are sub-rounded to rounded

o It shows clast-supported framework

o Matrix is made up of prismatic

crystals and is siliceous also seen

are perfectly rounded detrital

minerals.

Classification: Rudaceous

Formation: Mechanically/Chemically

formed

Composition:

o Large Clasts of Detrital quartz

o Microcline & Orthoclase feldspar

o Matrix is siliceous and contains

prismatic crystals

o Mafic bodies

o

Anisotropic Character:

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o Quartz is irregular and shows

interference color grey of 1st

order

o Microcline shows characteristic

‘tartan twinning’

o Orthoclase shows characteristic

‘lamellar twinning’

o Prismatic crystals are pleochroic

in shades of green, bluish-green,

sometimes yellow.

o They show interference colors of

2nd order purple, green.

o The prismatic crystals have

oblique extinction between 10-15

degrees.

Identification of the prismatic crystals in

thin section is a debatable topic and will be

discussed later on in the project.

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CHAPTER 3

DISCUSSION OF VARIOUS TOPICS

3.1 PALEOCURRENT ANALYSIS Many erosional and depositional sedimentary

structures can be used to deduce the direction

or trend of the currents that formed them.

Knowledge of Paleocurrents gives vital

information on the paleogeography; sediment

provenance and Paleocurrent patterns are

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restricted to particular depositional

environments. Some sedimentary structures are

vectorial i.e. they give the direction in which

the current was flowing; cross-stratification,

asymmetric ripples, flute marks, etc. Other

structures give the trend or line of direction

of the current these include parting lineation,

groove marks, symmetrical ripples, preferred

orientation of grains, pebbles and fossils.

Paleocurrent data was collected in the field by

simply measuring the orientation of the

structure using a clinometer.

We measured the orientation of the cross-beds

and found out that it was approx. oriented

towards S 45°W. Therefore the current must have

been logically flowing NE- SW. We also measured

preferred orientations of long axis of pebbles

in conglomerate and found that they were

oriented towards SW. Therefore, Paleocurrents

in the region moved from NE-SW.

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3.2 IDENTIFICATION OF PELLITIC AND PRISMATIC

CRYSTALS FOUND IN THIN SECTION OF

CONGLOMERATE

While doing microscopic studies of the thin

section of conglomerate from Bilgi, we came

across a bizarre occurrence of long, slender,

prismatic crystals and well rounded pellet-like

structures in the interstitial spaces between

the grains along with the siliceous matrix.

Some of the crystals were seen to be included

in quartz grains.

The prismatic crystals were seen having 1 set

of cleavage and have Bluish Green – Yellow

pleochroism under PPL and showed 2nd order

interference colors of purple, green and yellow

under XP light, also extinction angle of these

slender crystals is 8-14 degrees i.e. oblique

extinction. These crystals seem to be oriented

parallel to each other in some places and

haphazardly placed elsewhere.

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The pellet-like rounded structures are found

associated with these prismatic crystals and do

not show any preferred orientations. They

appear to be greenish-blue in color and are

pleochroic. They show high order interference

under XP light.

Identifying these minerals was a serious

problem for us, as our knowledge of geology is

restricted. But we made and attempt with the

help of our teachers.

Since the crystals have a prismatic habit, 1

set of cleavage, oblique extinction,

Pleochroism and high order interference we

probably expect them to be made of the

amphibole - actinolite, which in the case must

be of DETRITAL origin. Another possibility is

the occurrence of Glaucophane - Riebekite which

matches the above description but these

minerals are commonly associated with

metamorphism and must be detrital.

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We have come to a conclusion that the crystals

maybe Actinolite. We aren’t sure of the

conclusion because infrastructure limits us.

The green pellet-like structures are said to be

only shown by the mineral glauconite and

chlorite as per our reference from the book

“Introduction to Mineralogy- William D. Ness”

which says chlorite shows lower birefringence

than glauconite. If the pellets are AUTHIGENIC,

we can conclude that the pellet-like structures

are of the mineral glauconite.

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3.3 DISTICTION BETWEEN BAGALKOT SANDSTONES

AND BADAMI ARENITES

The bagalkot sandtones are mostly quartzitic

and the grains appear to be fused due to low

grade thermal metamorphism. The badamis on the

other hand are arenites and the grains are

coarser and distinct. The sediments in the

badamis are not indurated. The badamis are

horizontal whereas the bagalkots are inclined

with a dip amount of 10° due South West. The

bagalkot quarzitic sandstones show banding

between siliceous and ferruginous composition

whereas the badamis are composed only of

feldspar and quartz and no compositional

variation is seen in the matrix.

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3.4 OCCURRENCE OF PYRITE AND XENOLITHS IN

GRANITE

Known as fool’s gold because pyrite is

routinely misidentified as gold by the

uninitiated. Hardness, brittle character, and

greenish black streak is distinctive.

Pyrite is the most common sulfide mineral and

few hydrothermal deposits are without it.

Igneous rocks of any composition may contain

pyrite as an accessory mineral and it may form

magmatic segregations in some mafic intrusive

complexes. Pyrite is common as fine grains in

shale and is mostly precipitated from sea water

under reducing conditions. It is a very

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important mineral in process of supergene

enrichment.

Dark colored xenoliths are also seen which

could have gotten caught up in the rising magma

which ultimately cooled to form granites with

these xenoliths. The xenoliths must have come

from the older meta-sedimentaries.

3.5 STRATIGRAPHIC COLUMN

The basement is made up of coarse grained

granites. There is an unconformity of breccia

separating the bagalkots from the granites. The

bagalkots consists of quartzitic sandstones

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that show a variation in matrix composition

from siliceous to ferruginous. The ferruginous

quartzitic sandstones show incrustations on the

joint planes due to leaching of iron. The

ferruginous as well as siliceous quartzitic

sandstones show cross - bedded structure which

indicates the current direction. The siliceous

sandstones show current ripples indicating

shallow water deposition. Above the bagalkot

lies the unconformity of conglomerate that

separates the bagalkots from the badami

arenites. The direction in which the long axis

of the pebbles in the conglomerate indicates

the paleo-current direction. The conglomerate

is intercalated with the upper badami arenites

which indicates the basin of deposition was

fluctuating between subsidence and uplift of

the water body. The topmost beds comprise of

the badami arenites which are horizontally

deposited and composed of feldspar and quartz.

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