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PROVENANCE AND CLASTIC PETROFACIE9 OF WADHWAN FORMATION, SURENDRA NAGAR AREA. GUJARAT, INDIA Maittt of $]^Uos[opl^ IN GEOLOGY ARSHAD ZAMAN KHAN DEPARTMENT OF GEOLOGY ALIGAAH MUSLIM UNIVERSITY ALIGARH 1993
Transcript
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PROVENANCE AND CLASTIC PETROFACIE9 OF WADHWAN FORMATION, SURENDRA NAGAR

AREA. GUJARAT, INDIA

Maittt of $]^Uos[opl^ IN

GEOLOGY

ARSHAD ZAMAN KHAN

DEPARTMENT OF GEOLOGY ALIGAAH MUSLIM UNIVERSITY

ALIGARH

1993

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DS2243

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D E P A R T M E N T O F G E O L O G Y ALIGARH MUSLIM UNIVERSITY

ALIGARH—202 002

Ofited 15.^.8U..ia3_

CERTIFICATE

Research v/ork on this dissertation

Provenance and Clastic Petrofacies of Wadhwan

Formation, Surendra Nagar Area, Gujarat, India,

was carried out by Mr. Arshad Zaman Khan at the

Department of Geology, Aligarh Muslim

University, Aligarh under my supervision.

I certify that the research work is an

original contribution of the candidate and he

is allowed to submit the dissertation for the

award of M.Phil Degree of this University.

(DR. KHURSHED AKHTAR) M.Sc.(Luck. ) ,Ph.D.(Alig.)

Reader

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ACKNOWLEDGEMENTS

The author is grateful and deeply indebted to

Dr. Khurshed Akhtar, v/hose guidance and help at all the

time bring this work at the final stage.

The author is thankful to Professor S.N. Bhalla,

Chairman, Department of Geology^ . Aligarh Muslim

University/ Aligarh* for providing n^essary facilities

for research work.

Valuable help rendered by Dr. Shahid Farooq and

Dr. A.H.M. Ahmad/ Lecturers, Department of Geology/

A.M.U., Aligarh at various stages of this study requires

special mention.

Thanks are due to Dr». M.M. Khan, Mr. M. Alam and

Kazim Rangzan with whom the author had made a fruit ful

discussions at the time of work.

Lastly the author is thankful to Mr. H.S. Sharma

and Mr. Saleemuddln for taking up the job of typing and

drawing.

(ARSHAD^AMAN KHAN)

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CONTENTS

CHAPTER I

INTRODUCTION

REGIONAL GEOLOGICAL SETTING OF VVESTERN INDIA 1

SAURASHTRA BASIN 4

LOCATION OF THE STUDY AREA 10

AIM AND SCOPE OF WORK 11

CHAPTER II

TEXTURE OF THE WADHWAN SANDSTONE 14

TECHNIQUE AND DATA PRESENTATION 15

STATISTICAL PARAMETERS OF GRAIN SIZE 16

ROUNDNESS 24

SPHERICITY 26

TEXTURAL MATURITY 29

BIVARIANT PLOTS 31

GRAIN CONTACTS AND COMPACTION 35

CHAPTER III

DETRITAL COMPOSITION OF THE WADHWAN SANDSTONES

METHODOLOGY 40

FRAMEWORK GRAINS 41

CEMENTS (AUTHIGENIC) 49

FACTORS CONTROLLING THE DETRITAL MINERALOGY 52

CHATPER IV

PETROFACIES AND PROVENANCE INTERPRETATION 6 6

PETROFACIES 70

PLATE TECTONIC SETTING 75

CHAPTER 4

SUMMARY AND CONCLUSIONS 81

REFERENCES 89

APPENDICES 101

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XX

LIST OF TABLES

1. Generalized stratigraphic sequence of the

Saurashtra Penisula (After Biswas and Deshpande,

1983). 8

2. Statistical parameters of grain size

(percentile) of the Wadhwan sandstones. 17

3. Statistical parameters of grain size

distribution (M , (J^, SK^, K ) of the Wadhwan

sandstones based on Folk's (1980) method. 18

4. Roundness of sandsize detrital grains of the

Wadhv^an Sandstones. 25

5. Sphericity of the detrital grains of the

Wadhwan Sandstone. 27

6. Textural maturity of the Wadhwan sandstones. 30

7. Percentages of various types of grain to grain

contacts of the Wadhwan Sandstones. 37

8. Percentages of detrital minerals in the Wadhwan

Sandstones. 4 2

9. Percentage of detrital grains, clay, cements

and void spaces of the Wadhwan Sandstones. 50

10. Classification and symbols of grain types

(After Dickinson, 1985). 71

11. Percentage of detrital modes of the Wadhwan

sandstones (based on classification scheme of

Dickinson, 1985). 74

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.11

LIST OF FIGURES

1. Regional Tectonic map of Western India showing

prominent rift basins and Precambrian orogenic

trends (After Biswas and Deshpande, 1983). 2

2. Geologic and Tectonic map of Saurashtra

Pc- insula (After Biswas and Deshpande, 1983). '1

3. Composite histograms of statistical parameters

of grain size distribution of the VJadhv/an

Sandstones (A-Mean size, B-Sorting, C-Skev;ness

and D-Kurtosis). 2 0

4. Composite histogram of grain roundness of the

Wadhwan sandstones. 28

5. Composite histogram of grain sphericity of the

Wadhwan sandstones. 28

6. Bivariant plots of different textural parameters

of the Wadhwan sandstones (A-Mean size versus

roundness, B-Mean size versus sphericity, C-Mean

size versus sorting). 33

7. Bivariant plots of different textural parameters

of theWadhwan sandstones (A-sorting versus

sphericity,B-sorting versus roundness). 34

8. Photomicrograph shovi?ing mostly grain • to grain

point contacts in the Wadhwan sandstones (X-90,

crossed).

9. Photomicrograph of a typical recrystallized

metamorphic quartz grain in the Wadhwan

sandstones showing mostly equant subindividuals

(X-90, crossed). 44

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i V

10. Photomicrograph of a typical stretched

metamorphic quartz grain in the Wadhwan

sandstones showing elongated subindividuals

(X-90, crossed). # 44

11. Photomicrograph of ,a typical chert grains in the

Wadhwan sandstones chert has recrystallized to

microcrystalline quart; {X-90, crossed). 46

12. Photomicrograph of a pleochroic tourmaline grain

in the VJadhwan sandstone (X-90, uncrossed). 46

13. Scanning electron micrograph of the Wadhwan

sandstone showing well-developed hexagonal plates

of authegenic kaolinite arranged in vermicular

form.

14. Scanning electron micrograph of the Wadhwan

sandstone showing irregular aggregates of

allogenic kaolinite with rugged plate outlines.

Incipient silica overgrowths are seen on quartz

grain surfaces.

48

48

15. Photomicrograph of the Wadhwan sandstone showing

iron oxide cement filling up intergranular spaces

and fractures within the detrital quartz grains

(X-90, uncrossed). 51

16. Photomicrograph of the Wadhwan sandstone showing

oversized pore spaces lined with iron oxide

cement (X-90, uncrossed). 51

17. Photomicrograph of the Wadhwan sandstone showing

rare carbonate cement which has corroded detrital

quartz grains (X-90, crossed). 53

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18. Classification of the Wadhvi?an sandstones

(According to the scheme of Folk, 1980). 69

19. Classification of the Wadhwan sandstones (Based on

the scheme of Dickinson, 1985). ^2

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CHAPTER I

INTRODUCTION

REGIONAL GEOLOGICAL SETTING OF WESTERN INDIA

In many parts of the world including India the

Mesozoic Era is a tectonically important Era. Pangea which

existed in Palaeozoic Era was gradually torn apart during

Mesozoic Era v/ith the opening of Proto-Atlantic and Proto-

Indian Oceans. The separation of North America and Gondwana-

land took place in Late-Triassic Period. Gondwanaland itself

dismembered in Late-Jurassic resulting in the separation of

India and Africa from Australia, Antarctica and South

America.

The breakup of Gondwanaland along with opening of

Indian Ocean and northward drift of India with the final

detachment from East Africa/Madagascar and Antarctica were

discussed by many authors (Norton and Sclater, 1979; Patriat

and Segoufin, 1988; Powell et al, 1988; Scotese et al. 1988;

Westermann, 1988).

At different stages of evolution of the Indian

subcontinent during Mesozoic times three prominent rift

basins were formed in the western periphery of Indian

peninsula (Biswas 1982). The rift basins of western India

including Narmada, Cambay and Kutch are styled by three

principal Precambrian erogenic trends and their reactivation

in Mesozoic and Tertiary times (Fig. 1).

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gt^^

», BOMBAY HIGH ^1^'rjr-SA

^ "%

\

l -n

0 1 0 0 2 9 OKm

Precombrion Tectonic Trend Rift Faults With Downthrow Major Structurol Trend Within Ri f t System

F i g . l , : Regional Tectonic map of Western Ind ia showing prominent r i f t ba s in s and Precambrian orogenic t r e n d s (After Biswas and Deshpande, 1983) .

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The major tectonic boundry which divides the Indian

shield into a southern peninsular block and a northern

foreland block is the ENE-WSW Narmada-Sone lineament which

is parallel to Satpura orogenic trend (West 1962; Mathur et

al. 1968). The Narmada rift is formed in western part of

this megalineament by a fault parallel to the lineament.

This rift continues south of the Saurashtra block. The west

coast fault parallel to the NNW-SSE Dharwar trend is

responsible for shaping the present coastline. A series of

extension faults on the western Indian continental shelf,

which are sub-parallel to the Dharwar trend, have given rise

to horsts and grabens which are typical of a passive margin

(Pratsch, 1978; Biswas, 1982). The West coast fault extends

northward across the Narmada rift and forms the Cambay rift.

The Gulf of Cambay is considered as a trijunction with

Cambay basin as the aborted rift. The third important

Precambrian trend, the NE-SW Delhi-Aravalli trend continues

across Cambay basin into the Saurashtra platform.

The major events of plate tectonic activity and

development of the rift basins were synchronous (Pratsch,

1978; Biswas, 1982). The tectonic evolution of the basins

have been correlated v;ith the stages of - drifting of the

Indian plate since the time of its breakup from Gondwana-

land and till its collision with Eurasia. The rifting

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developed progressively from north to south around

Saurashtra horst. The Kutch basin was formed in Early

Jurassic, followed by Cambay basin in Early Cretaceous.

Saurashtra area remained as a horst between Kutch and

Narmada basins till Early Cretaceous when it became a

depositional basin.

The Mesozoic sedimentation in Kutch-Saurashtra-

Cambay area was terminated by a major tectonic episode which

was accompanied by the extrusion of flood basalts (Deccan

Trap) during Late Cretaceous-Early Paleocene time.

SAURASHTRA BASIN

The Saurashtra basin which forms a horst block is

bounded by Kutch and Cambay rift basins to its north and

east respectively and by Surat depression to the south

(Fig. 1). The southern WSW^ENE trending fault is an

extension of Narmada geofracture. Towards western part of

the basin no major fault exists and it gradually deepens in

that direction. The Saurashtra basin is surrounded on three

sides by the Gulf of Kutch, Arabian sea and Gulf of Cambay

whereas the Gujarat alluvial plains extend to its

northeastern limit. The Precambrian basement of the basin

forms an ENE-WSW trending arch which plunges WSW.

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Tectonic history

The transgression of sea into the coastal areas of

other parts of Gondwanaland during Jurassic-Cretaceous time

also invaded parts of the western margin of the Indian plate

(Krishnan 1960). At the same time Kutch basin opened up to

the north of the Saurashtra Peninsula which was uplifted and

a shallow epicontinental Jurassic sea ingressed into the

Kutch basin (Bisv/as, 1987; Krishna, 1987). The Saurashtra

basin developed in Early Cretaceous coinciding with uplift

of northerly Jurassic basin. The elongated Saurashtra rift

basin extending southwest to northeast from Gujarat coast to

Aravalli over a length of nearly 400 Km and bounded by major

faults to north and south (Biswas, 1982; Varadarajan and

Ganju, 198 9) represents a pericratonic composite rift system

(Sengor et al, 1978).

According to Cannon et al. (1981) and Tankard et al.

(1982) the beginning of plate separation in other parts of

the Gondwanaland during Jurassic and Early Cretaceous was

marked by the formation of pericratonic rift basins which

were similar to the pericratonic rifts (Kutch and

Saurashtra) of India.

Both of these basins (Kutch and Saurashtra) may

represent parts of an elongated extensional trough where up

and down rifting during Jurassic - Cretaceous time brought

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about basin formation and sedimentation, first in northern

part (Jurassic of Kutch) and latter in southern part (Early

Cretaceous of Saurashtra) (Casshyap and Aslam, 1992).

Stratigraphy and Age

The Saurashtra basin comprises Mesozoic and Tertiary

sedimentary rocks and the Deccan Trap basaltic flows, the

later covering the major part of the Saurashtra Peninsula

(Fig. 2). The Mesozoic sedimentary rocks outcrop only in the

northeastern part of the Saurashtra peninsula. In the

outcrop area, the Mesozoic sequence is nearly 600 ra thick.

Besides the outcrop around Surendranagar, these rocks extend

in subsurface below the Alluvium (Recent) and Deccan basalt

(Late Cretaceous) towards the eastnortheast-westsouthwest

and north and south.

The Mesozoic sedimentary rocks which are exposed in

the northeastern part of the Saurashtra basin comprise two

formations: Dharangadhra Formation and Wadhwan Formation,

which are unconformably overlain by the Deccan Traps of Late

Cretaceous age. Thin Neogene and Quaternary deposits occur

along the Arabian Sea coast of the Saurashtra peninsula. The

generalised complete stratigraphic sequence of Saurashtra

peninsula is given in Table 1.

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7 0^ 72^

23 • D h r a n g a d h r a

S u r e n d r a n a g a r Wadhwan

DWQ

22'

Porbanda

20 0 20 AO • — I 1 I

Kms

LEGEND

ALLUVIUM

PLEISTOCENE

^ PLIOCENE] EOCENE (LATERITE)

MIOCENE [ V ^ V ] (^^f.l^'^.^fOUS PALAEOCENE

APPROXIMATE POSITION OF PRECAMBRIAN BASEMENT ARCH

)

1 OHRANGAOMRA DOME 2 BHAUNAGAR NOSE 3 GOGHA NOSE

Gulf of Cambay

MeS020lC

Fiy.2t Geologic and Tectonic map of Saurashtra Peninsula (After Biswas and Deshpande, 1983).

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Table 1: Generalised stratigraphic sequence of the

Saurashtra peninsula (after Biswas and Deshpande,

1983)

Age Formation

Recent to subrecent Alluvium

Unconformity

Quaternary Porbandar Formation

Unconformity

Mio-Pliocene Dwaraka Formation

Early Miocene Gaj Formation

Unconformity

Paleocene (?) Laterites

Unconformity—

Late Cretaceous Decoan Trap Foirmation (Basaltic flows)

-Unconformity-

Early Cretaceous Wadhwan Formation Dhrangadhra Formation

Unconformity

Precambrian Basement

The Dhrangadhra Formation which is more than 500 m

thick mainly comprises coarse elastics with minor amount of

shale and clay. The overlying Wadhwan Formation, about 50 m

thick, is made up of brick red to reddish brown sandstones

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with small pockets of shales, and at places thin brownish

grey limestones are developed. The Wadhwan Formation is

overlain by Deccan Trap basalt flows. The Mesozoic

sedimentary sequence of the Saurashtra basin ranges in age

from Late Jurassic to Early Cretaceous (Upper Tithonian to

Albian: 145-97 m.y.). The Dharangadhra and Wadhwan Formation

are correlated with Bhuj Formation and Ukra Member of Bhuj

Formation. Marine fossils of Wadhwan Formation reported by

Chiplonkar and Borokar (1975) were correlated with those

fossils found in the Bagh beds and upper part of Nimar

Sandstone (Chiplonkar et al. 1977). Thus the Wadhwan and

Bagh sediments may be synchronous in age.

Palaeoclimate, Palaeogeography and Depositional Environmen-ts

The palaeogeographic reconstruction of the earth at

100 m.y. by Thompson and Barron (1981) shows that in

Cretaceous period the Surendranagar area was located at 44°

latitude, south of the equator, which lies within the wide

humid tropical belt. At this latitude the average annual

temperature was estimated as 21°C.

Palaeogeographic evolution of Mesozoic rocks in

Saurashtra basin was reconstructed on the basis of

lithofacies and palaeocurrent study by Casshyap and Aslam

(1992) .

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10

The sedimentation in Saurashtra during Early

Cretaceous time started with deltaic environment which is

represented by Dharangadhra Formation. The deltaic

environment was follov>red by a short marine transgressive

phase of Aptian-Albian age which resulted in the deposition

of Wadhwan Formation, which is correlated with the

transgression of Kutch basin represented by Ukra beds

According to Casshyap et al. (1983), the Cretaceous

sedimentation in Saurashtra rift began with*the deposition of

shoreline conglomerate, and interbedded sandstone and shale

around Himatnagar near Aravalli highlands. The sedimentation

followed southwestward which is represented by dominance of

sandstone.

The calcareous lenses of coral and bryozoa in

uppermost Wadhwan Formation suggest onshore marine

ingression during the course of Wadhwan sedimentation.

Progressive downwarping of the basin may account for

transgression of shoreline environment towards northeast as

sedimentation progressed through time.

LOCATION OF STUDY AREA

Saurashtra basin is one of the three prominent

basins of western India. It is bounded by the Kutch and

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11

Cambay rift basins to the north and east and Surat

depression to the south. It is the \7esternm0st basin in

peninsular India where the strata have been refered to as

Mesozoic Gondwana rocks (Pascoe, 1959). The basin extends

for about 400 km from Aravalli highland in the northeast to

the Gujarat coast in the southwest.

The study area (Surendranagar) lies on the northeast

part of the Saurashtra basin. It is situated about 200

kilometer southwest of Ahmadabad on the State Highway. It is

well connected with the other tov/ns of the area by private

and government road transport agencies. Excellent exposures

of the VJadhwan Formation are found in the sandstone quarries

located around the Surendranagar town (Longitude 71°50' and

Latitude 22^48').. Several of these quarries were visited and

representative samples of the VJadhwan Sandstone were

collected.

AIM AND SCOPE OF WORK

' The Cretaceous rocks of Gujarat have been

extensively studied for the purpose of depositional

environment and facies interpretation (Aslam, 1987; Ahmad

and Akhtar 1990; Casshyap and Aslam, 1992) but very little

research work has been carriedout on the provenance and

petrofacies evoluation of clastic rocks in general and

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12

Mesozoic rocks of Gujarat in particular (Akhtar and Ahmad

1991; Akhtar et al, 1992).

The present study of the sandstones of Wadhwan

Formation of Surendranagar area mainly aims to reconstruct

their provenance and plate tectonic setting of their

deposition on the basis of petrofacies study. A critical

study of various factors influencing the provenance

interpretation has also been made.

The field work \\?as carried out for the purpose of

the collection of sandstone samples from different quarries

located around the Surendranagar town.

Thin sections prepared from 36 sandstone samples

from study area v/ere used for petrographic study. Textural

attributes of the sandstones were determined and included

grain size analysis and estimation of grain roundness.

Statistical parameters of grain size were computed with the

help of cumulative frequency curves and formulae according

to the method of Folk (1980).

For petrographic classification of the sandstones

and provenance interpretation, their detrital mineralogy was

studied. Folk's(1980) scheme of classification based on

composition of the detrital constituents and Dickinson's

(1985) classification emphasing the tectonic setting of

provenance were used.

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13

Diagenetic processes of the sandstones were studied

with a view to checking the modification of detrital

mineralogy by diagenetic processes and their effect on

provenance interpretation.

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CHAPTER II

TEXTURE OF THE WADHWAN SANDSTONES

A Study of texture of the Wadhwan sandstones was

taken up in view of the fact that the texture and

composition of detrital sediments are controlled by

provenance and other factors, such as transportation,

depositional environment and diagenesis (Suttner 1974).

The textural study of the VJadhwan sandstones

included their grain size analysis. A large number of

v;orkers have studied grain size distribution of clastic

sediments. Their studies were mainly related to hydrodynamic

conditions, processes and environments of deposition of

clastic sediments. Review of grain size parameters and their

relation v/ith depositional processes have been published by

Folk (1966), Visher (1969) and Friedman (1979).

The dependence of sandstone detrital modes on grain

size has been demonstrated by several workers (Blatt, 1967;

Young et al, 1975; Basu, 1976; Mack and Suttner, 1977).

The grains of various sizes may be produced by the

processes of rock disintegration and modified by other

processes like transportation and deposition. Some rocks

characteristically yield grains and detritus of different

sizes. For example, disintegration of quartzite will produce

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15

blocks vi?hile other rocks (coarse grained acid igneous rocks

and gneisess) may undergo granular disintegration and yield

sand size grains. Smalley (1966) pointedout that size

distribution of quartz must be closely restricted by the

size distribution of quartz in the crystalline rocks of

source area.

The textural attributes of the VJadhwan sandstones/

such as size, roundness and sphericity were studied with a

view to interpreting the provenance of the sandstones, and

estimating the influence of texture on the detrital modes

and petrofacies. Interrelationship of various textural

attributes of the Wadhwan sandstones were studied with the

help of bivariant plots.

TECHNIQUES AND DATA PRERSENTATION

Different techniques of size measurement apply to

widely different size ranges. Riviere (1977) has described

various techniques for grain size measurements.

36 sandstone samples of Wadhv/an Formation were used

for grain size analysis. Thin sections were used for grain

size analysis because samples being hard enough were not

easily disaggregated. The examination of thin sections

showed that the original fabric is largely preserved. As a

whole there is a little modification of texture either by

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16

reaction between the grains and cement, or by mechanical

compaction.

The grain size measurements were carried out with

the help of a micrometer eye piece, and 300 to 400 grains

were point counted per thin section. The present study

employed phi (0 ) scale and the size data was grouped into

half phi ih ^ ) class intervals.

Statistical parameters of grain size distribution

were determined with the help of cumulative frequency curve

plotted on the basis of grain size data. For plotting the

curves, grain size in phi ( f6 ) units was represented on the

X-axis and cumulative frequency percent on y-axis. From the

cumulative frequency curves the phi ( ^ ) units represented

by 9i5, yJ16, 025, f650, f675, 084, 095 percentiles were read

(Table 2). Statistical parameters of grain size were

calculated with the help of formulae given by Folk (1980).

The calculated parameters included Graphic mean (M )

inclusive graphic standard deviation (CJ-, ), inclusive graphic

skewness (SK_) and Graphic Kurtosis (K_) (Table 3). i G

STATISTICAL PARAMETERS OF GRAIN SIZE

Folk's (1980) statistical parameters of grain size

determined for the Wadhwan sandstones samples are described

as follows:

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Table 2: Statistical parameters of grain size (Percentiles) of

the Wadhwan sandstones.

SainplG No'.

Q2 03 04 09 10 12 13 14 15 16 17 18 20 21 22 23 24 25 29 30 31 32 33 34 36 39 41 42 43 44 45 46 47 49 50 55

izJ5

- 0 . 1 5 0 . 1 0 . 2 0 . 4 0 . 1 5

- 0 . 7 5 0 . 4 5 0 . 1 5 0 . 3 5 0 . 1 5 0 . 2 5 0 . 7 5 0 . 0 0 . 2 0 . 0 5 0 . 7

- 0 . 2 5 0 . 1 5 0 . 8 0 . 2 5 1 . 1 0 . 4 5 1 . 4 0 . 8 5 0 . 3 0 . 1 0 . 0 5 0 . 3 0 . 4 0 . 8 0 . 0 1 . 3 0 . 7 5 0 . 3 5 0 . 0

- 0 . 4 5

jzJ16

0 . 4 0 . 9 0 . 8 1 . 0 5 0 . 7 5

- 0 . 1 5 1 . 0 5 0 . 8 0 . 7 5 0 . 7 0 . 7 5 1 . 0 0 . 4 0 . 5 5 0 . 8 5 1 . 3 5 0 . 0 0 . 5 1 . 2 0 . 7 5 1 . 8 0 . 8 5 1 . 7 1 . 3 0 . 8 5 0 . 4 5 0 . 4 5 0 . 7 0 . 8 1 . 1 0 . 5 1 . 5 5 1 . 2 0 . 6 1 . 1 0 . 1

(z$25

0 . 7 5 1 . 3 1 . 0 1 . 3 1 . 0 0 . 1 1 . 3 0 1 . 0 5 0 . 9 0 . 9 5 0 . 9 5 1 . 2 5 0 . 6 5 0 . 7 5 1 . 1 1 . 6 5 0 . 2 0 . 7 1 . 4 5 0 . 9 5 2 . 0 1 . 0 1 . 9 5 1 . 5 1 . 1 0 . 6 0 . 6 5 0 . 9 5 1 . 0 5 1 . 3 0 . 8 5 1 . 8 1 . 5 0 . 9 1 . 5 5 0 . 5 5

jzJ50

1 . 4 5 1 . 4 5 1 . 6 1 . 9 5 1 . 5 0 . 8 5 1 . 9 1 . 8 0 1 . 3 5 1 . 5 1 . 3 5 1 . 8 1 . 3 5 1 . 3 1 . 6 2 . 1 5 0 . 9 1 . 5 5 2 . 0 1 . 6 2 . 4 5 1 . 5 2 . 4 5 2 . 0 1 . 6 5 1 . 0 1 . 1 1 . 6 5 1 . 6 1 . 7 5 1 . 5 2 . 1 2 . 1 5 1 . 6 2 . 3 1 . 7

jz$75

2 . 5 2 . 0 2 . 3 5 2 . 4 2 . 3 5 1 . 6 5 2 . 5 2 . 1 5 2 . 1 2 . 3 5 2 . 0 5 2 . 4 5 2 . 2 5 2 . 1 5 2 . 2 2 . 8 2 . 1 2 . 5 5 2 . 6 2 . 3 3 . 2 5 2 . 2 2 . 9 5 2 . 4 5 2 . 5 5 1 . 7 1 . 8 5 2 . 2 5 2 . 4 5 2 . 3 5 2 . 2 2 . 5 5 2 . 6 2 . 1 5 2 . 7 5 2 . 6 5

tz$84

2 . 8 2 . 2 5 2 . 7 5 2 . 7 2 . 7 5 1 . 9 5 2 . 8 5 2 . 4 0 2 . 3 5 2 . 7 5 2 . 4 5 2 . 8 2 . 7 5 2 . 5 2 . 6 3 . 0 5 2 . 5 5 3 . 1 2 . 9 5 2 . 7 3 . 7 2 . 6 5 3 . 3 2 . 6 5 3 . 1 2 . 0 5 2 . 2 5 2 . 5 0 3 . 0 5 2 . 7 5 2 . 4 5 2 . 7 5 2 . 9 2 . 4 3 . 0 5 3 . 3

jzJ95

3 . 3 2 . 7 3 . 7 5 3 . 6 5 3 . 5 2 . 8 3 . 6 5 3 . 0 5 2 . 7 5 3 . 6 2 . 8 5 4 . 0 3 . 5 3 . 9 3 . 7 5 3 . 9 5 3 . 2 5 3 . 9 3 . 9 5 4 . 0 5 4 . 3 5 3 . 4 3 . 8 5 3 . 1 5 3 . 8 5 2 . 6 5 3 . 2 5 2 . 9 4 . 1 5 3 . 8 2 . 9 5 3 . 4 5 3 . 5 5 2 . 9 4 . 1 5 4 . 4

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Table 3: Statistical paramctcrn of grain size distribution of Hadhwan sandstones based on Folk'i

(1968) method (graphic incluaiv* graphic standard deviation - O", , inolualm

graphic skcwness • SK., graphic kurtosls •KG)

!IO. Verbal limit Verbfll Limit SK, Verbal U n i t Verbal limit

02 03 04 09 10

12 13 14 15 16 17 18 20 21

22 23 24

25 29 30 31 32 33 34

36 39. 41

42 43

44 45 46

47 49 50 55

1.55

1.50 1.7 1.9 1.6

0.88 1.93 1.66 1.4 1.65 1.5 1.8 1.5 r.45

1.6 2.18 1.15

1.7 2.05 1.6 2.65 1 .66 2.48 1.98

1.86 1-16 1.26

1.6 1.81

1.86 1.48 2.1

2.08 1.53 2.15 1.7

Medium Mertiura Medium MeHiun Mvrtlum

COflrsp Medium Medium Medium Medium Medium Medium Medium Medium

Medium Fine Medium

Medium Fine Medium Fine Medi urn Fine Medium

Medium Medium Medium

Medium Medium

Medium Medium Fine

Fine Medium Fine Medium

1.12 0.72 1.01 0.89 1.0

1.05 0.93 0.8 0.76 1.0 0.79 0.9 1.11 1.04

0.99 0.91 1.16

1.21 0.9 1.05 0.96 0.89 0.77 0.67

1.09 0.78 0.93

0.84 1.12

0.86 0.92 0.62

0.84 0.83 1.1 1.53

Poorly sorted Moderately sorted Poorly sorted Moderately sorted Modaratoly sorted

Poorly sorted Moderately sorted Moderately sorted Moderately sorted Moderately sorted Moderately sorted Moderately sorted Poorly sorted Poorly sorted

Moderately sorted Moderately sorted Poorly sorted

Poorly sorted Moderately sorted Poorly sorted Moderately sorted Moderately sorted Moderately sorted Moderately well sorted Poorly sorted Moderately sorted Moderately sorted

Moderately sorted ' Poorly sorted

Moderately sorted Moderately sorted • Moderately well sorted Moderately sorted • Moderately sorted • Poorly sorted Poorly sorted

0,13 Fine skewed 0.08 Near symmetrical 0.18 Fine skewed

-0.02 Hoar symmetrical 1.09 Strongly Fine

skewed 0.06 Near symmetrical

-0.09 Near symmetrical -0.18 Coarse skewed 0.2 Fine skewed 0.20 Fine skewed 0.21 Fine skewed 0.22 Fine skewed 0.2 Fine skewed 0.31 Strongly fine

skewed 0.15 Fine skewed 0.07 Near symmetrical 0.31 Strongly fine

skewed 0.21 Fine skewed 0.15 Fine skewed 0.2 Fine skewed 0.23 Fine skewed 0.27 Fine skewed 0.1 Fine skewed

-0.01 Near symmetrical

0.25 Fine skewed 0.28 Fine skewed 0.3 Strongly fine

skewed -0.03 Near symmetrical 0.32 Strongly fine

skewed 0.28 Fine skewed -0.01 Near symmetrical 0.16 Fine skewed

•0.05 Near symmetrical •0.04 Near symmetrical -0.16 Coarse skewed 0.05 Near symmetrical

0.80 1.50 1.10 1.2 1.0

93 09 70 82 01 0 22 89

1.08

1.38 1.16 0.76

83 12 18 06 01 0 0

0 95 10

.83 ,09

17 92 17

1.0 0.83 1.43 0.9

Platy kurtic Lepto kurtic Mesokurtic Lspto kurtic Mesokurtic

Mesokurtic Mesokurtic Platy kurtic Platy kurtic Mesokurtic Mesokurtic Lepto kurtic Platy kurtic Mesokurtic

Lepto kurtic Lepto kurtic Platy kurtic

Platy kurtic Lepto kurtic Lepto kurtic Mesokurtic Mesokurtic Medokurtic Mesokurtic

Mesokurtic Mesokurtic Mesokurtic

Platy kurtic Mesokurtic

Lepto kurtic Mesokurtic Lepto kurtic

Mesokurtic Platy kurtic Lepto kurtic Mesokurtic

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Graphic Mean (M )

Folk (1980) proposed the Graphic Mean (M^) as a

measure of average size. This parameter is much better than

the median, because it is based on three points and gives a

better overall picture and it is much easier to determine

as compared to the mean computed by the method of moments.

Mean size of sandstones under study was calculated on the

basis of the following formula devised by Folk (1980).

M z

^16 + ^50 - 84

The sandstones were classified on the basis of

verbal limits of grain size proposed by Folk (1980).

The Graphic Mean (M ) of various samples from the

study area ranges from 0.88 to 2.65 ^ (Table 3). The mean

size of 78 percent of samples falls within the medium sand

range and 19 percent belong to fine sand and only 3 percent

fall within the coarse sand range (Fig. 3A). Thus, the

sandstone^ are mainly medium grained and some are fine

grained. Coarse grained sandstones are rare.

Inclusive Graphic Standard Deviation ( O", )

Inclusive Graphic Standard Deviation as a measure of

sorting of sediments was proposed by Folk (1980). Sorting is

determined by dispersion around central tendency. Because

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TOO

80

£ 60 u

a> A O

20

0

A

1

Mean s i ze

1

100

80

60

AO

20

0

B

S o r t i n g

1 C M F PS MS MWS

100

80

c 60 it u i AO

20

0

Skewness

SFS FS NS CS

100

80

60

^0

20

0

D

Kurtosis

M

Fiy. 3: Composite histograms of statistical parameters of grain size distribution of the Wadhwan sandstones

A - Mean size (C=coarse grained, M = medium grained, F = Fine grained)

B - Sorting (PS= poorly sorted, MS=Moderately sorted, MWS = moderately well sorted)

C - Skewness (SFS = Strongly fine skev/ed, FS = Fine skewed, NS = near symmetrical, CS = coarse skev/ed).

D - Kurtosis (P = Platykurtic, M= Mesokurtic, L=Leptokurtic)

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the tails of a distribution have been thought to be

environmentally sensitive, estimates of sorting have been

designed to reflect them.

The inclusive graphic standard deviation of grain

size was calculated with the help of Folk's (1980) formula

given below:

Q- = _^84_1_^16_ _ 1 95 - < 5 6.6

The samples were also classified according to the

verbal limits proposed by Folk (1980).

Inclusive graphic standard deviation values of

samples under study range from 0.62 to 1.53 f6. Out of 36

samples, 22 samples (61.0%) are moderately sorted, 12

samples (33.0%) poorly sorted and 2 samples (6.0%)

moderately v ;ell sorted (Fig. 3B). Thus, the sandstones are

mainly moderately to poorly sorted.

Sorting of sediments generally depends upon

stability and competency of currents. If currents are of

'relatively constant strength, sediments will be very well

sorted to well sorted but fluctuating currents will give

rise to poorer sorting. In the Wadhwan sandstones most of

the samples are moderately sorted to poorly sorted which

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indicate that the currents were not strong and persistent

enough to produce a well sorted sediment.

Inclusive Graphic Skewness {SK_)

The asymmetry of distribution is measured by

skewness and is determined by the relative importance of the

tails of the distribution. The skewness or asymmetry is also

determined by the position of the mean with respect to

median. The skewness is negative and the sample is coarse

skewed when the mean is located towards the coarse side of

the median. When skewness value is positive, the sample is

described as fine skewed because the mean is located towards

the finer side of the median.

Skewness of the sandstones under study was

calculated on the basis of the following formula devised by

Folk (1980).

I +

The sandstones were classified on the basis of

verbal limits of skewness proposed by Folk(1980).

Inclusive graphic Skewness (SK^) values of the

samples under study range from - 0.01 to 1.0 fi. Out of 36

samples, 5 samples (14.0%) are strongly fine skewed, 18

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samples (50%) are fine skewed, 11 samples (30.0%) are near

symmetrical and 2 samples (6.0%) are coarse skewed (Table 3

and Fig. 3C). Thus, majority of the samples are fine skewed.

Graphic Kurtosis (K^)

Kurtosis is a measure of peakedness of the

distribution and measures the ratio between the sorting in

the tails of the curves and sorting in the central position.

If the central position is better sorted than the tails, the

curve is said to be excessively peaked or Leptokurtic; when

tails are better sorted than the central portion, curve is

deficiently or flatpeaked and platykurtic.

Kurtosis of the sandstones understudy Vi?as

calculated on the basis of the following formula devised by

Folk (1980).

J 95 " " 5 ^G

2.44 (jz5 5- izi25)

The sandstones were classified on the basis of

verbal limits of kurtosis proposed by Folk (1980).

The kurtosis values of the studied samples range

from 0.70 to 1.5 «J. Out of 36 samples, 8 samples (22.0%)

are platykurtic, 18 samples (50.0%) are mesokurtic and 10

samples (28%) are leptokurtic (Table 3 and Fig. 3D). Thus,

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mesokurtic samples are dominant and the rest are almost

equally divided leptokurtic and platykurtic ones.

ROUNDNESS

Roundness of grain depends upon the sharpness of its

edges and corners. In many cases roundness have been used

interchangeably with shape but roundness is different from

and independant of shape.

Wentv/orth (1919) first clearly defined roundness and

quantitatively measured it as ^i/'^ii where r is the radius

of curvature of the sharpest edge and R^ is one half the

longest diameter.

Wadell (1935) defined roundness as the ratio of the

average radius of curvature of the several corners and edges

to the radius of curvature of the inscribed sphere. But both

Wentv/orth's and Wadell's methods for determining the

roundness require measurements in three dimensions and thus

are difficult, cumbersome, and time-consuming.

Russel and Taylor (1937), Krumbein (1940), Powers

(1953) employed tvi?o-dimensional images of particles for

estimating roundness. Russel and Taylor (1937) proposed five

roundness classes but their class limits were not

systematically chosen and arthmatic means of the class

intervals v/ere used as mid points. Krumbein (1940) presented

nine different roundness values which were however very close

together.

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Table 4i Roundnoon of dotrltnl grains of the Hadhwan sandstones, Surondranagar area (Roundness

clasncn according to Powers' scale)

Eamplf Total Vory angular Angular Subangular Subroundod Rounded Well rounded Mean Ho. grain (0.12 - 0.17) (0.17-0.25) (0.25-0.37) (0.37-0.49) (0.49-0.70)(0.70 - 1.0) Roundness

N N i N % N « N % N 8 N i

02 03 04 09 10 12 13 14 15 16 17 ic 20 21 22 23 24 25 29 30 31 32 33 34 36 39 41 42 43 44 45 46 47 49 50 55

94 18.3 126 115 99 109 101 105 126 145 112 120 136 112 115 121 67 69 120 172 llfl 125 131 136 144 124 102 118 112 122 124 139 136 141 124 112

7 9 11 6 6 9 7 5 13 14 11 7 9 6 12 3 8 6 11 12 10 12 11 19 16 13 9 12 12 14 12 20 17 21 23 15

8 7 9 5 6 8 7 5 10 10 10 6 7 5 10 2 12 8 9 7 8 10 8 14 11 10 9 10 11 11 10 15 12 15 19 13

19 29 15 17 10 13 23 9 27 38 24 32 21 16 29 18 12 15 23 21 23 28 23 28 33 33 20 26 22 35 30 25 28 26 26 24

20 22 12 15 10 12 23 8 21 26 21 27 15 14 25 15 18 22 19 12 20 22 18 21 23 27 20 22 20 29 24 18 21 18 21 22

22 32 23 31 22 29 26 20 46 39 26 39 45 40 34 42 21 17 27 48 30 30 26 31 34 39 28 28 26 29 33 27 31 29 34 25

23 24 18 27 22 27 26 19 36 26 23 32 33 36 30 35 31 25 22 28 25 24 20 23 24 31 27 24 23 24 27 19 23 21 27 22

26 38 51 44 45 45 31 52 15 30 37 32 42 43 28 43 16 24 32 65 31 35 44 42 46 2B 25 25 31 22 27 27 35 39 27 27

28 28 40 38 46 41 31 50 12 21 33 27 31 38 25 36 24 35 27 38 26 28 34 31 32 23 24 21 28 18 22 19 26 28 22 24

16 20 17 14 12 10 8 14 15 20 11 8 11 4 8 9 6 5 19 21 16 15 19 10 12 B 14 20 14 14 18 28 19 20 8 15

17 15 14 12 12 9 8 13 12 14 10 6 8 4 7 7 9 7 16 12 14 12 14 7 8 7 14 17 12 11 14 20 14 14 6 13

4

e 9 3 4 3 6 5 11 4 3 2 8 3 4 6 4 2 8 5 8 5 8 6 3 3 6 7 7 8 4 12 6 f. 6 6

4 4 7 3 4 3 6 5 9 3 3 2 6 3 3 5 6 3 7 3 7 4 6 4 2 2 6 6 6 7 3 9 4 4 5 6

0.38 0.37 0.40 0.38 0.39 0.37 0.36 0.41 0.36 0.34 0.35 0.33 0.37 0.35 0.33 0.38 0.35 0.35 0.38 0.38 0.38 0.36 0.39 0.34 0.34 0.32 0.37 0.38 0.37 0.35 0.35 0.39 0.35 0.36 0.32 0.36

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In the present study roundness scale given by Powers

(1953) has been used. This scale has six roundness grades in

such a way that the class limits closely approximate a y/2

geometric scale. Mean roundness of each sample was determined

by conventional statistical method employing the Powers'

class limits values.

The roundness of detrital particles of the Wadhwan

sandstones was measured in 2S samples and average of about

100 grains per thin section were measured.

The roundness data and mean roundness of individual

sample is given in Table 4. in various samples roundness of

grains ranges from very angular to well rounded. But in most

samples majority of the grains are subangular to subrounded.

The generalized grain roundness distribution based on

aggregate data of all the 36 samples is unimodal (Fig. 4).

The modal class of the aggregate distribution is subrounded

class. Mean roundness of individual samples range from 0.32

to 0.41 and for aggregate distribution the mean roundness is

0.36.

SPHERICITY

Sphericity of a particle might be defined as s/S

where s is the surface area of the sphere of the same volume

as the particle in question, and S is the actual surface area

of the particle.

Wadell (1935) proposed a sphericity index given by

the formula dn/Ds where dn, is the diameter of the sphere

with the same volume as the object and Ds is the diameter of

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Table 5: Sphericity of detrital grains of Wadhwan

Surendranagar area

sandstones,

Sanple No

02 03 04 09 10 12 13 14 15 16 17 18 20 21 22 23 24 25 29 30 31 32 33 34 36 39 41 42 43 44 45 46 47 49 50 55

Total No. of grains

N

94 134 126 115 99 109 101 105 126 145 112 120 136 112 115 121 67 69 120 172 IIB 125 131 136 144 124 102 117 112 112 124 139 136 141 124 112

High >

No.

42 58 53 27 29 28 20 15 34 27 22 20 27 21 27 31 19 17 24 45 28 23 27 28 21 30 25 37 28 27 26 36 28 28 37 19

sphericity (0.9)

%

45 43 42 23 29 26 20 14 27 19 20 20 20 19 27 26 28 25 20 26 24 18 21 21 15 24 25 31 25 22 21 26 21 20 30 17

Low sphericity <(0.3)

No.

52 78 73 88 70 81 81 90 92 118 90 100 109 91 88 90 48 52 96 127 90 102 104 108 123 94 77 81 84 95 98 103 108 113 87 93

%

55 57 58 77 71 74 80 86 73 81 80 80 80 81 77 74 72 75 80 74 76 82 79 79 85 76 75 69 75 78 79 74 79 80 70 83

Mean sphericity

0.56 0.56 0.55 0.44 0.47 0.45 0.41 0.38 0.46 0.41 0.41 0.40 0.41 0.41 0.44 0.45 0.47 0.44 0.42 0.45 0.44 0.41 0.42 0.42 0.38 0.44 0.44 0.49 0.45 0.43 0.42 0.45 0.42 0.41 0.47 0.40

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100. 28

80

60 c

Q- 40

V A = Very A n g u l a r

A = A n g u l a r

S A = S u b A n g u l a r

SR = S u b R o u n d e d

R = R o u n d e d

W : W e l l R o u n d e d

F i g . 4 : Composite histogram of grain roundness of the Wadhwan sandstones.

20

0 L VA SA SR WR

100

80

^ 60

(J

a. AO

20

Fig. 5:

Composite histogram of grain sphericity of the Wadhwan sandstones,

LOW HIGH

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circumscribed sphere. All these methods of expressing

sphericity require measurements which can not be done on

sand grains.

In the present study, sphericity of the various

grains was classified as low and high as suggested by

Powers' (1953) comparison chart (Table 5). The mean

sphericity values of the grains in the studied sandstones

range from 0.38 to 0.56. The composite histogram shows that

majority of the grains are of low sphericity (Fig. 5). About

75% grains are of low sphericity and 25% grains are of high

sphericity.

TEXTURAL MATURITY

Texture of the sediments have two aspects:

(1) description of properties (grain size, shape etc) and

(2) integration of these properties into an assumed

sequential development, comprising the four stages of

textural maturity (Folk, 1980). According to this concept,

as sediments suffer a greater input of mechanical energy

through abrasive and sorting action of waves or currents,

they pass sequentially through the four stages, from

immature to submature, mature and supermature stage.

The sediment is texturally immature if it contains

over 5% terrigenous clay matrix and poorly sorted and

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Tabla (i T*Ktaral BCtttrity of aandstonas, Madhwan formation (Lowar CraCacaoua), Suraadranaqar «z«a

Saai>l

Xo.

02 03 04 09 10 12 13 14 IS 1«

n 18 20 21 22 23 24 2S 29 30 31 32 33 34

3i 39 41 42 43 44 4S 4(

47 49 SO

ss

. " , < * >

l.JS 1 .so 1.7 1.» l.« 0.8S 1.93 1.66 1.4 1.6S l.S 1.8 1.5 1.4S 1.6 2.18 I.IS 1.7 2.OS 1.6 2.6S 1.66 2.48 1.98

1.86 1.16 1.26 1.6 1.81 1.86 1.48 2;i

3.08 1.S3 2.IS 1.7

Kaan alia

Kadlua Madlua Hadlua Hadluai MadluB Coaraa Hadlua MadiiiH Hadiua Hadiua Hadlua Hadiua Hadiua Nadlua Hadiua rinc Hedlua Hedlua rina Hadiua rina Hadiua Flna Hadiua

Hadiua Hadiua Hadiua Hadiua Hadiua Hadiua Hadiua rina

rina Hadiua rina Hadiua

Clay «

3.0

-2.0 1.0

-1.0 1.0 2.0 2.0 1.0 2.0 2.0 1.0 1.0 1.0 1.0 3.0 1.0 2.0 1.0 2.0

--2.0

2.0 1.0

-2.0 3.0 2.0 1.0 7.0

1.0 3.0 3.0 1.0

s<

1.13 0.72 1.01 0.89 1.0 1.05 0.93 0.80 0.76 1.0 0.79 0.9 1.11 1.04 0.99 0.91 1.16 1.21 0.9 1.05 0.96 0.89 0.77 0.67

1.09 0.78 0.93 0.84 1.12 0.86 0.92 0.62

0.84 0.83 1.1 1.S3

Sorting ^ Haan Noundnaaa of grain

TaHtural aaturlty

Poorly aortad Modarataly aortad Poorly aortad Hodarataly aortad Hodarataly aortad Poorly aortad Hodarataly aortad Hodarataly aortad Hodarataly aortad Hodarataly aorted Hodarataly aortad Hodarataly aortad Poorly aortad Poorly aortad Hodarataly aortad Hodarataly aortad Poorly aorted Poorly aortad Modarataly aortad Poorly aortad Hodarataly aorted Modarataly corted Modarataly aorted Hodarataly wall aortad Poorly aortad Hodarataly aortad Moderately aorted Hodarataly aorted Poorly aorted Moderately aorted Moderately aorted Moderately well aorted Moderately aorted Moderately aorted Poorly aorted Poorly aorted

0 0 0 0 0 0 0 0 0 0 0 0. 0 0. 0. 0. 0, 0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0.

.38

.37

.40

.38

.39

.37

.36

.41

.36

.34

.35

.33

.37

.35

.33

.38

.35

.35

.38

.38 38 .36 39 34

34 32 37 38 37 35 35 39

36 36 32 36

Subrounded Subroundad Subrounded Subrounded Subrounded Subrounded Subangular Subroundad Subangular Subangular Subangular Subangular Subrounded Subangular Subangular Subrounded Subangular Subangular Subroundad Subrounded Subrounded Subangular Subrounded Subangular

Subangular Subangular Subrounded Subrounded Subrounded Subangular Subangular Subroundad

Subangular Subangular Subangular Subangular

Subaatura Mature Subaatura Suboiatura Hatur* Subaatura Subaatura Subauiture Subaatura Suboiatura Subaatura Subaatura Subawture Subnature Subaatura SubaMtura Subaiature Subaatura Subaiature Subaature Subnature Mature Mature Subawtura

Subaatura Subaatura Mature Subaatura Subaatura Subaiature Subautura laaature

Subaature sufaaatoce Subaatura Subaatura

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angular sand grains. In submature stage, sediments contain

under 5% clay but grains are poorly sorted and not well

rounded; while in mature stage sediments contain little or

no clay and sand grains are well sorted but not rounded. The

supermature stage of sediments contains well sorted and well

rounded sandgrains with no clay.

Out of a total 36 studied sandstone samples, 29

samples (80%) are submature, 6 samples (17%) are mature and

only one sample (3%) is immature (Table 6).

BIVARIANT PLOTS

To show the interrelationship of various textural

attributes, the bivariant plotswere used. Different textural

parameters were plotted against each other and their

relationship \i?as determined statistically by computing their

correlation coefficient values, following Karl Pearson's

correlation coefficient method:

r = Six y

E x X ^ y

A computer programe in Fortron 77 language was

developed using Vax-11/780 computing system.

The different plots which were used for the Wadhwan

sandstones included, mean size versus roundness, mean size

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versus sphericity, mean size versus sorting, sorting versus

sphericity, and sorting versus roundness.

Mean Size Versus Roundness

For the study of the relationship between mean size

and roundness of the studied sandstones, 36 samples were

used and their mean size were plotted against their mean

roundness. The correlation coefficient determined for the

plot (0.19) shows a weak relation between the size and

roundness (Fig. 6A) . Roundness of the grains increases as

their size decreases.

Mean Size Versus Sphericity

The mean size versus sphericity diagram shows a

poor inverse relationship (Fig. 6B). This statement is

verified by the correlation coefficient value (-0.15)

determined for the plot. As the size of the grains

decreases, their sphericity increases.

Mean Size Versus Sorting

The mean size versus sorting plot of the studied

sandstones shows a very weak inverse relationship (Fig. 6C)

with a correlation coefficient of -0.16. The inverse

relationship suggests that sorting of the sand grains

increases with a decrease in their size.

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3.0

0,30 0.35 0./.0 0 A 5 M E A N R O U N D N E S S INCREASES —

3 0

2 0

1 0

.« . * •

• • ^ • •

0 0 J I I L.

r = - 0 , 15

0.35

3.0

20

0.45 0.55 0.6 5 MEAN SPHCniCITV I N C R E A S E S »

. • a* .

10

00 L

r - - 0 IC

0 60 0.80 VO 1.2 SORTING ( ^ ) OF C R E A S E S - >•

"' l.>. VG

Fig. 6: Bivariant plots of different textural parameters of the Wadhwan sandstones (A-Mean size versus roundness, B-Mean size versus sphericity, C-Mean size versus sorting).

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34

0.60

0.50

2 •* O.AO 3

0.35 0.60

• • • • • •

• • • • • o

• • • • • • • • • • •

0,80 1.0 1.2 SORT1NO(0) D E C R E A S E S >-

r - 0.A6

].i. 1.6

0.A5

O-AO

<

z 0.35

0.30

B

• %i • • •

• * • • •• • «• • •

• • • o

• • •

0.6 0

<•= - 0 . 1 2

.0.80 1.0 1.2 S O R T I N G [^ ) D E C R E A S E S »-

1.^ 1.6

Fig. 7: Bivariant plots of different textural parameters of the VJadhwan sandstones (A-sorting versus sphericity, B-sorting versus roundness).

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Sphericity versus Sorting

Sphericity plotted against sorting and

correlation coefficient value for the plot (0.46) shows a

medium relationship between sorting and sphericity of the

Wadhwan sandstones (Fig. 7A). Sorting of the grain decreases

as their sphericity increases.

Roundness versus Sorting

The bivariant plot of roundness versus sorting has

a correlation coefficient value of -0.12 which shows weak

relationship between sorting and roundness (Fig. 7B ) Sorting

of the grain decreases as their roundness decreases.

It may be summarized that within the size range of

the Wadhwan sandstones, which is mainly medium sand, a

decrease in mean size is attended by an increase in

roundness and sphericity and a decrease in sorting. Whereas

a decrease in sorting is accompanied by a decrease in

roundness and an increase in sphericity.

GRAIN CONTACTS AND COMPACTION

Compaction may bring about crushing of soft

detrital grains, especially pelitic rock fragments resulting

in the formation of pseudomatrix. Thus, compaction may

modify the original framework composition of a sandstone and

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36

present a problem in the interpretation of such a rock.

Therefore, a study of compaction of the Wadhwan sandstones

was also undertaken to evaluate the effect of diagenetic

processes on sandstone composition.

Compaction is a process of pore volume reduction in

sediments due to over burden load (Chilingarian/ 1983).

Compaction includes bgth mechanical as well as chemical

compaction (pressure solution).

Grain to grain contacts of sediments give an idea

about pore space reduction and compaction history of

sediment. Taylor (1950) classified the grain contacts as

floating, point, long, concavo-convex and sutured.

Grain contacts of the Wadhwan sandstones were

studied in 36 thin sections for determination of the

compactional history of the formation. Type of grain

contacts (Taylor 1950) were recognized and their pecentages

were detemined in diffrent samples (Table 7).

Ip various samples of the Wadhwan sandstones,

floating grains range from 2.0 to 21.0 percent and average

about 7.9% of the total grain contacts. High percentages of

floating grains in few samples are largely the result of

modification of texture by reaction between cement and

grains.

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Table 7: Percentage of various types of grain to grain contacts,

Wadhwan sandstones

Sanple No.

02 03 04 09 10 12 13 14 15 16 17 18 20 21 22 23 24 25 29 30 31 32 33 34 36 39 41 42 43 44 45 46 47 49 50 55

Floating

9.0 4.0 4.0 3.0 7.0 4.0 6.0 9.0 4.0 3.0 19.0 5.0 6.0 3.0 9.0 2.0 3.0 14.0 16.0 7.0 8.0 4.0 12.0 11.0 4.0 3.0 11.0 12.0 7.0 6.0 18.0 14.0 7.0 9.0 3.0 21.0

Point contact

47.0 57.0 64.0 73.0 62.0 78.0 81.0 65.0 70.0 78.0 57.0 66.0 58.0 74.0 57.0 74.0 61.0 63.0 38.0 43.0 70.0 77.0 36.0 62.0 68.0 57.0 55.0 65.0 65.0 68.0 33.0 64.0 39.0 44.0 59.0 41.0

Long contact

35.0 34.0 23.0 18.0 25.0 13.0 9.0

23.0 19.0 15.0 18.0 20.0 33.0 17.0 26.0 18.0 28.0 12.0 38.0 42.0 14.0 13.0 42.0 22.0 22.0 31.0 22.0 15.0 23.0 21.0 33.0 15.0 47.0 39.0 30.0 27.0

Concavo-convex contact

4.0 2.0 3.0 2.0 2.0 2.0 2.0 1.0 3.0 2.0 3.0 3.0 1.0 2.0 2.0 3.0 2.0 4.0 3.0 1.0 3.0 2.0 3.0 1.0 2.0 1.0 3.0 2.0 2.0 2.0 3.0 2.0 2.0 4.0 2.0 2.0

Suture contact

5.0 3.0 6.0 4.0 4.0 3.0 2.0 2.0 4.0 2.0 3.0 6.0 2.0 4.0 6.0 3.0 6.0 7.0 5.0 7.0 5.0 4.0 7.0 4.0 4.0 8.0 9.0 6.0 3.0 3.0 13.0 5.0 5.0 4.0 6.0 9.0

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Point contacts range from 33.0 to 81,0 percent and

average 60.25 percent (Fig. 8); while long contacts vary

betv^een 9.0 to 47.0 percent and average 24.50 percent.

Concavo-convex and sutured contacts are not very common. The

average percentages of sutured and concavo-convex contacts

are 4.90 percent and 2.3 percent respectively.

Taylor (1950) suggested that floating grains and

tangential (point) contacts represent original packing. The

long contacts may be the product of either original packing

or little pressure and precipitated cement. The concavo-

convex and sutured contacts are the result of overburden

pressure and compaction.

In the Wadhwan sandstones floating and point graih

contacts together form about 68.0 percent. Abundance of

these contacts suggests that little compaction has taken

place and original texture and packing are largely

preserved.

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Fig. 8: Photoinicroyraph showing mostly grain to grain point contacts in the Wadhwan sandstones (X-90, crossed).

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CHAPTER III

DETRITAL COMPOSITION OF THE WADHWAN SANDSTONES

Sandstones are mixtures of mineral grains and rock

fragments coming from disaggregated products of erosion of

rocks of all kinds. The processes determining mineral

composition of sandstones are more complex than simple mining

ones from source areas of different kinds.

Minerals may be lost or modified by weathering in

source area, by transportation to site of sedimentation and

by diagenesis.

Mineralogy of a sandstone is the derived product from

the source area as modified by sedimentary processes. A

mineraological examination is one of the most practical

studies that can be made to obtain information on provenance,

including tectonism and climate, effect of transportation

including distance and direction and addition of chemically

deposited minerals during sedimentation and diagenesis.

METHODOLOGY

Detrital composition of the Wadhwan sandstones was

evaluated both quantitatively and qualitatively in 36 thin

sections. About 200-300 grains per thin section were counted

for quantitative analysis and for determining the modal

composition of rocks under investigation.

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Terminology proposed by Folk (1980) was followed for

identifying and describing the detrital grains of the

sandstones.

FRAMEWORK GRAINS

The sandstones of the Wadhwan Formation are composed

of mainly quartz of several varieties followed by micas,

rock fragments, feldspars and heavy minerals as minor

constituents. The average composition of the sandstones is:

quartz, 98.24%; rock fragments, 1.0%; feldspars, 0.19%; and

other minor constituents (mica and heavy minerals etc),

0.57% (Table 8) .

Quartz

Quartz is the dominant framework constituent of the

sandstones, forming on an average of about 98.24% of the

rocks. On the basis of Folk's (1980) classification the

various types of quartz recognized include common quartz,

vein quartz, recrystallized metamorphic quartz and stretched

metamorphic quartz. The average percentages of various types

of quartz are: common quartz, 88.62%; vein quartz, 3.96%;

recrystallized metamorphic quartz, 4.25%; stretched

metamorphic quartz 3.15%.

Common Quartz

The common quartz occurs as subequant and mostly

subangular to subrounded grains. The grains are

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Table 8: Percentages of detrital minerals in the Wadhwan Sandstones

Sample No.

02 03 04 09 10 12 13 14 15 16 17 18 20 21 22 23 24 25 29 30 31 32 33 34 36 39 41 42 43 44 45 46 47 49 50 55

Quartz-tall

Common quar

92 94 89 84 80 77 82 78 78 86 86 87 96 81 95 90 80 87 94 92 94 89 93 86 92 74 86 83 83 96 85 85 92 93 91 90

tz

Monocrys-ine Vein quartz

2 2 1 5 6 7 8 5 6 6 4 4 1 3 1 5 9 2 1 1 2 2 1 6 4 6 6 8 '8

-3 6 -

1 1 2

Quartz-tall

Recrysta-llized metamor-phic quartz

3 2 6 5 8 9 3 5 5 5 7 4 2 8 2 3 6 7 1 3 3 3 2 4 2 9 4 4 5 2 4 3 2 1 5 4

•Polycrys-ine Stretched metamor-phic quartz

1 1 1 5 4 6 4 10 8 2 3 3 1 7 1 1 5 2 2 2 — 3 1 3 1 9 3 3 3 -

4 2 2 2 3 2

MicQ

-----------------

1 --1 1 --— -

1 --

1 1 ---

1

Feld­spar

_

----—

1 — --— -— — -— --— -— -— --

2 1 — --

1 -

2 — -

-

Rock fra­gment

1 -

2 -

2 1 1 2 3 1 -2 —

1 1 1 — — — 1 1 2 1 1 1 _ -

1 1 2 1 1 2 2 -

1

Heavy mine­ral

1 1 1 1 -—

1 — ----— — -— — 2 1 1 — -

1 .r»

-w

-— -—

1 2 —

1 -

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monocrystalline with clear appearance having few inclusions

of tourmaline, mica and opaques. It forms 74.0 to 96.0%

(average 87.2%) by volume in different samples.

Vein quartz

It consists of 1.0 to 9.0% (average 3.9%) of the

detrital fraction. It occurs in the form of monocrystalline

grains. These grains have abundant vacuoles imparting a

cloudy appearance.

Recrystallized Metamorphic Quartz

It occurs in the form of polycrystalline grains of

fine to coarse size and equant to sub-equant shape. The

grains are made up of a mosaic of microcrystalline to fine

grained subindividuals (Fig. 9). It comprises 1.0 to 9.0%

(average 4.19%) of the total detrital constituents of the

Wadhwan sandstones.

Stretched metamorphic quartz

It occurs as polycrystalline grains which are mostly

made up of elongated and lensoid subindividuals of micro-

quartz and fine grained quartz. The subindividuals have

subparallel to almost parallel orientation with sutured

boundaries and show highly undulose extinction (Fig. 10). It

constitutes generally 1.0 to 10.0% (average 3.1%) of

detrital fraction.

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Fig. 9: Photomicrograph of a typical recrystallized metamorphic quartz grain in the Wadhwan sandstones showing mostly equant subindividuals (X-90, crossed).

Fig. 10: Photomicrograph of a typical I stretched metamorphic quartz

grain in the Wadhwan sandstones showing elongated subindividuals (X-90, crossed).

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Mica

Both muscovite and biotite occur as tiny flakes. The

percentage of mica is very low in the Wadhwan sandstones,

averaging about 0.19% of the detrital constituents. However,

muscovite is more common than biotite. ' ~

Feldspars

In the studied sandstones feldspars are not common.

They are present only in some samples and constitute 1.0 to

2.0% of the detrital component averaging 0.19%. The feldspar

grains belong to mainly orthoclase. The grains are

weathered. Kaolinite is common in the Wadhwan sandstones and

possibly formed by the weathering of feldspars grains.

Rock Fragments

In the Wadhwan sandstones rock fragments are present

in almost all the samples except few of them. The rock

fragments comprise 1.0 to 3.0% and average 1.0%. Both

sedimentary and metamorphic rock fragments occur in the

studied sandstones. Sedimentary rock fragments include

mainly chert (Fig. 11) and some siltstone. Low rank

metamorphic rock fragments include phyllite and quartzite

fragments.

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Fig. H : Photomicrograph of typical chert grains in the Wadhwan sandstones, Chert has recrystallized to microcrystalline quartz (X-90, crossed).

Fig. 12: Photomicrograph of a pleochroic tourmaline grain in the VJadhwan sandstones (X-90, uncrossed).

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Heavy Minerals

Heavy minerals were observed in about one third of

the total samples. Heavy minerals constitute 1.0 to 2.0% and

average 0.31%. Opaques, tourmaline (Fig. 12) and zircon are

the main types of heavy minerals.

Clay Matrix

Percentages of clay in the Wadhwan sandstones

generally range from. 1.0 to 7.0 percent/ and average about

1.6 percent.

The clay minerals in sandstones can originate either

as detrital particles brought into the basin of deposition

as a result of erosion and redistribution of rocks or by

insitu alteration of unstable grains such as feldspars,

micas etc. or deposited from solution in intergranular pores

of sediments during diagenesis as an interstitial cement.

In the Wadhwan sandstones both allogenic and

authigenic clays are present. The authigenic kaolinite is

dominant and shows well' L developed crystalline habit and

book form as is clearly seen in SEM photographs (Fig. 13)

which distinguish it from allogenic clay. The allogenic

kaolinite shows irregular aggregates of plates which have

rugged outlines (Fig. 14).

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Fig. 13: Scanning electron micrograph of the Wadhwan sandstone showing well-developed hexagonal plates of authigenic kaolinite arranged in vermicular form.

Fig. 14; Scanning electron micrograph of the Wadhwan sandstones showing irregular aggregates of allogenic kaolinite with rugged plate outlines. Incipient silica overgrovv ths are seen on quartz grain surface.

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CEMENTS (AUTHIGEHIC)

In the Wadhwan sandstones three types of cementing

materials occur which include iron oxide/ silica and

calcite, in order of abundance.

Iron oxide

In the Wadhwan sandstones iron oxide is most

abundant cementing material which forms 2.0 to 25.0%

(average 6.5%) by volume of the rocks (Table 9).

Iron oxide cement occurs in the form of a thin

coating around detrital grains as well as patches which

show corrosion of detrital grains and replacement along

fractures (Fig. 15). Corroded quartz grains suggest the

presence of an earlier calcite cement which was replaced by

iron oxide. In some thin sections oversized pore spaces are

seen to be lined with a thin coating of iron oxide (Pig»

16).

The ove^fsized pore spaces have resulted from

destruction and leaching of labile framework grains,

possibly feldspars.

Iron oxide cement was possibly derived from

weathering and leaching of the overlying traps. The thin

iron oxide coating on detrital grains is possibly inherited

from the source rocks.

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Table 9: Percentages of detrital grains, clay, cements and

spaces of the Wadhwan sandstones Void

Sampl-e No

02 03 04 09 10 12 13 14 15 16 17 18 20 21 22 23 24 25 29 30 31 32 33 34 36 39 41 42 43 44 45 46 47 49 50 55

Detrital grain

77 83 83 73 82 87 86 86 78 85 87 86 77 81 76 61 83 84 80 84 69 79 83 f2 ly) wf 0^ ' 82 80 72 81 87 64 80 79 80

Clay

3 -2 1

1 1 2 2 1 2 2 1 1 1 1 3 1 2 1 2 -• 2 2 1 «• 2 2 2 1 7 1 3 2 1

Iron Oxide Cement

4 6 6

11 7 2 3 2 5 4 7 5 8 6 9 6 7 5 4 5

15 10 9 8 8 4 f 3 S -8 -25 6 8 9

Silica Cement

2 2 1 2 2 1 2 2 1 2 1 1 1 2 1 2 2 3 2 1 4 2 1 4 1 2 2 2 1 3 2 2 3 1 2 —

Carbonate Cement

__ ---

^

-------— ----------mm

--* — 21 -----2

Void Space

14 9 8

13 9 9 8 8

14 8 3 6

13 10 13 10 5 7

12 9

10 9 7 4 9 7 5

11 12 2 8 4 7

10 9 8

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Fig, 15: Photomicrograph of the Wadhwan sandstones showing iron oxide cement filling up intergranular spaces and fractures within the detrital quartz grains (X-90, uncrossed).

Fig. 16: Photomicrograph of the Wadhwan sandstone showing oversized pore spaces lined with iron oxide cement (X-90, uncrossed).

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Silica cement

Silica cement in the studied sandstones generally

ranges from 1.0 to 4.0% and averages about 1.86 percent. In

most of the samples silica cement occurs in the form of

quartz overgrowths. The authigenic quartz overgrowths on

detrital quartz grains are seen and observed to partially

fillup the intergranular spaces. SEM micrographs of quartz

grain surfaces show incipient silica overgrowth (Figs. 13

and 14) .

Carbonate cement

Calcite cement occurs in few samples of the Wadhwan

Formation. These are generally white coloured sandstones. In

thin section calcite cement show patchy distribution and

ranges in percentage from 2.0 to 21.0 and averages about

0.63%.

The calcite cement has partially replaced detrital

grains which are marked by corroded boundaries (Fig. 17).

The replacement cementation implies chemical instability of

quartz grains and slow rate of cementation resulting in

solution of the silica grains (Dapples, 1971).

FACTORS CONTROLLING THE DETRITAL MINERALOGY OF THE WADHWAN

SANDSTONES

Detrital mineralogy does not depend only on a single

factor but a group of factors are responsible for detrital

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Fig. 17: Photomicrograph of the Wadhwan sandstone showing rare carbonate cement which has corroded detrital quartz grains {X-90, crossed).

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composition of a sandstone which include the types of source

rocks, distance of transport , tectonism, palaeoclimate/

palaeogeography and depositional environments and diagenetic

modifications of the original detrital constituents.

Identification of the Source Area

In order to interprete the detrital mineralogy of a

sandstone in terms of the provenance/ one has to find out

where and at what distance was the source area* located and

what was its relation to the configuration and bathymetry of

the depositional basin. In other words we have to

reconstruct the palaeogeography of the time period during

the deposition of a particular sandstone formation. For

this we need to ascertain the paleoslope, paleocurrent

system operative during the depositional process and the

facies distribution.

The Cretaceous rocks of Saurashtra including the

Wadhwan sandstones were deposited in a failed rift and a

schematic model of its tectonic setting and broad

paleogeography have been reconstructed by Casshyap and Aslam

(1992). The commencement of Cretaceous sedimentation in the

Saurashtra rift was marked by the deposition of shoreline

conglomerate and interbeded sandstone and shale around

Himatnagar near Aravalli highlands (Casshyap et al 1983).

The study area lies about 150 kilometer southwest of

Himatnagar. Towards southwest sedimentation continued in the

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subsiding distal parts of the rift. A considerably thick

clastic sequence was deposited within the rift which shows

an increasing proportion of fine clastic to the southwest

along the length of the basin.

The paleogeographic reconstruction of the Saurashtra

rift suggests that the provenance of the Wadhwan sandstones

was located towards the northeast, in the Aravalli highlands

a few hundred kilometers from the study area.

Source Rock Composition

Each type of source rock tends to yield a

distinctive suite of minerals which constitute a guide to

the character of that rock. Both light and heavy minerals

of a sandstone are important in the study of provenance.

The quartz isand is the main product of rock

disintegration and decomposition and is the dominant

constituent of most sands. A number of attempts have been

made to utilize quartz as a guide to the provenance. Among

the earlier notable attempts Krynine'-s (1946) approach is

based on grain shape, character of the inclusions and

extinction. It v/as presumed that a discrimination between

igneous (plutonic) and .metamorphic origins of common

monocrystalline quartz could be made based on inclusions,

shape and extinction (undulatory or not). But these critaria

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are usually difficult to apply (Bokman, 1952). Quartz of

source rocks shows that difference in inclusions, shape and

extinction either do not exist or there is a wide range of

variation.

Many workers have emphasized the usefulness of

polycrystalline or composite quartz that is those grains

which are composed of more than one crystal unit (Blatt and

Christie, 1963; Conolly 1965; Voll, 1960). Polycrystalline

quartz showing tv/o distinctly different sizes of crystals

v;ithin a single grain is diagonastic of metamorphic quartz.

High ratio of polycrystalline quartz to total quartz also

suggests a metamorphic source. Voll (1960) has noted that

polycrystalline quartz of metamorphic origin is of two

types: (1) polygonized quartz in which component grains form

polygonal units, with straight boundaries which tend to meet

at 120 degree angles; and (2) polycrystalline quartz which

exhibit sutured boundaries.

Feldspar is the second most common mineral of sand.

Based on zoning, intergrowth habits, twining, fracturing

etc. the feldspars are defined into nine classes. Type of

zoning or/and lack of zoning may be clues to the provenance

of the feldspar (Pittnan, 1963). "Ehe plagioclase in volcanic

and hypabyssal rocks is characterized by oscillatory zoning,

v here as this type of zoning is rare in plutonic igneous and

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metamorphic rocks. Zoned plavioclase is strongly Indicative

of an igneous rock.

Feldspars are very sensitive to the v/eathering

processes which require not only suitable climate but also a

proper length of tine. The duration of time through which

processes of decomposition act is determined by relief. The

presence or absence of feldspar is therefore the result of

the balance between the rate of erosion and decomposition.

Detrital feldspar is therefore an index of both climatic

vigor and tectonism.

The micas are never a major constituent of

sandstone. They are derived from schists and gneisses, from

plutonic igneous rocks and from volcanic sources. Muscovite

is more common in sand than biotite, because of its greater

stability. In general, abundant mica suggests a metamorphic

provenance for the sand.

Besides the quartz and feldspa?", sandstones commonly

contain rock fragments. These may be volcanic, or be

sedimentary mainly pelitic particles and also be

metamorphic such as slate, phylite and mica schists.

The heavy minerals of sandstone have long been used

as indices of provenance and that certain species are i I

characteristics of certain source rocks is a well

established conclusion (Folk, 1980).

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The Wadhwan sandstones consist of igneous quartz

(common quartz, vein quartz), metamorphic quartz

(recrystallized metamorphic quartz, stretched metamorphic

quartz), micas and rock fragments.

The common quartz is dominant in the Wadhwan

sandstones. Common quartz is derived mainly from granite

batholith or granite-gneisses. Vein quartz, recrystallized

metamorphic quartz and stretched metamorphic quartz occur in

low percentages in the Wadhwan sandstones. Vein quartz in

the Wadhwan sandstones suggests derivation from pegmatites,

hydrothermal and rarely sedimentary vein fillings.

Recrystallized metamorphic quartz indicates origin from

recrystallized metaquartzite, highly metamorphosed granite and

gneissic rocks. Stretched metamorphic quartz of the studied

sediments is probably derived from granites, schists or

quartz veins.

Mica in the Wadhwan sandstones include mainly

muscovite and few biotite grains which might have been

derived frpm granites, pegmatite or schists.

Rarity of feldspar and very small amounts of rock

fragments in the Wadhwan sandstones indicate prolonged

abrasion or high intensity of weathering in the source area.

To the north and northeast of Himatnagar, where

Cretaceous sedimentation began in the Saurashtra rift,

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Precambrian rocks of Delhi and Aravalli Supergroup outcrop.

Around Himatnagar the Cretaceous sedimentary rocks rest on

the Precambrian basement with a pronounced unconformity.

The Precambrian rocks identified as the provenance of

/7adhwan sandstones consist of mainly quartzites and

ohyllites which have been intruded by the Idar granite. Thus

on the basis of present day distribution of Precambrian

rock types in combination with detrital mineralogy of the

sandstones it may be concluded that most of the Cretaceous

sediment was derived from metasedimentary rocks and granites

and granite-gneisses.

Tectonism

The effect of tectonism on detrital mineralogy of

the Wadhwan sandstones has been discussed in detail in the

following chapter of this dissertation which deals with

petrofacies and plate tectonic setting of the sandstones.

Distance of Transport

The residues produced by disintegration and

decomposition of source rocks are subjected to further

changes during their transport from the place of release

from a source rock to the place of their ultimate

deposition. The processes operative during transport not

only bring about rounding of the detritus but also modify

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the composition by selective abrasion. Downstream changes in

composition of river gravels have long been noted. Gravels

can become compositionally mature in a relatively short

distance of travel by rapid elimination of less durable

components v ith resulting enrichment in more stable rock

types.

On the other hand, evidence concerning the selective

wear and elimination of minerals in sand range is some what

ambiguous. Large streams show few or no changes in mineral

composition even during prolonged transport and feable

changes that do occur are not the result of differential

abrasion (Russell, 1939). There appears to be only a small

loss of feldspar relative to quartz and no appreciable loss

of other relatively soft and cleavable minerals. However,

other VN orkers have shown that there is an appreciable loss

of feldspar in comparatively short distance in high gradient

gravel-carrying streams (Plumblay, 1948).

The detrital grains of the Wadhwan sandstones are in

the sand size range and in all probability they have

undergone transportation for a distance of a few hundred

kilometers. The Wadhwan sandstones are deficient in

feldspars and one possible reason for this deficiency may be

the transportation of sediment by high gradient streams and

rapid destruction of feldspars by abrasion. Since deposition

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of the Wadhwan sandstones took place in a tectonically

active rift, presence of high gradient stream is quite

likely within the basin. However this premise does not stand

to scrutiny because rock fragments which could have been

destroyed more easily are more common than the feldspars.

Therefore some factor other than transportation was

responsible for the paucity of feldspars in the Wadhwan

sandstones.

Palaeoclimate

Climate is an important factor that controls the

detrital mineralogy of clastic rocks because the type of

weathering is dependent on climate. Under tropical

conditions where temperature is high and moisture is most

abundant, weathering appears to be most intense. Most

feldspars and labile constituents are destroyed and

sediments become enriched in quartz which is the only

chemically and physically durable mineral. Whereas colder or

more arid climates are marked by products of lesser

maturity. The general absence of water tends to retard

chemical action.

Palaeoclimate of the Cretaceous period was studied

by different workers who selected different parameters for

palaeoclimate reconstruction. Among the various parameters,

the latitudinal position is considered as the most important

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factor. The palaeogeographic reconstruction of the earth at

100 m.y. (Thompson and Barron, 1981) suggests that during

the Lower Cretaceous the study area was located at latitude

44° south of the equator and within the wide humid tropical

belt with luxuriant plant life that extended upto 45° north

and south of the equator. Therefore the Precambrian basement

rocks which provided sediments to the Saurashtra rift must

have undergone rigorous weathering under humid tropical

conditions resulting in destruction of much of the feldspars

and labile constituents. Palaeoclimate was possibly a very

important factor in the formation of highly quartzose

sandstones of the Wadhwan Formation. Akhtar and Ahmad (1991)

have demonstrated the active role played by tropical climate

in the deposition of quartz rich Nimar Sandstone which is

believed to be equivalent in age to the Wadhwan Formation.

Depositional Environments

The Lower Cretaceous rocks of the Saurashtra rift

basin represent deposits of a general tansgression

proceeding' from SW to NE consequent upon progressive

downwarping with intermittent rifting of the basin. A large

part of the lithofacies of the riftrfill represents

deposition in the nearshore coastal delta plain with a

gradual northeastward transgression recognized by the facies

changes from the basal deposits to the upper most Wadhwan

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Formation. The Wadhwan Formation represents localized

deposition in estuaries and embayments as part of continuing

marine transgression. The highlands to the east and

northeast supplied the clastic sediments into the estuarine

environment. Deposits of shoals and sand bars are

represented by the associated pebbly coarse sand.

Depositional reworking effects the relative

abundance of detrital grains in terrigenous sediments

(Suttner, 1974). The most effective modification of

sandstone composition may take place in those environments

where rates of erosion and sedimentation are low. A long

residence time at the sediment water interface of shallow

marine environments enhances the destruction " of labile

detrital grains (Suttner et al. 1981). The sandstones of

Wadhwan Formation which are mostly texturally submature

might have been deposited in rather protected environments

of estuaries and embayments. Therefore, it seems that

depositional reworking has not been very effective in

controlling the detrital composition of the Wadhwan

sandstones which show a very high degree of compositional

maturity but lack the same degree of textural maturity.

Diagenetic Modifications

The depositional composition of sands may be altered

by diagenetic processes which must be taken into

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consideration while making provenance interpretation

(McBride, 1985). The modifying diagenetic processes operate

from the zone of weathering to the deep subsurface where

diagenesis grades into metarraorphism. Many authors including

Blatt, 1966; Fuchtbauer, 1967, 1974; Nagtegall, 1978;

Chilingarian, 1983; McBride, 1985; and Akhtar at al, 1992

have studied the diagenetic processes and their effects on

modification of detrital composition. The diagenetic

modifications include loss of detrital framework grains by

dissolution, alteration of grains by replacement or

recrystallization, and the loss of identity of certain

ductile grains during compaction which give rise to

pseudomatrix.

The presence of highly weathered feldspar grains

as~well-as oversize pores indicate dissolution of detrital

grains in the Wadhwan sandstones. I have estimated that

about 2% of the existing porosity of the Wadhwan sandstones

has resulted from dissolution of detrital grains, mainly

feldspars.. The process of replacement has not been very

effective in modifying the detrital composition of the

Wadhwan sandstones. The replacement of quartz grain by

carbonate and iron oxide is only partial and localized and

hence composition of the original grain is determinable.

Therefore this factor has not been much of a problem in

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provenance interpretation of the Wadhwan sandstones. A study

of grain contacts of the Wadhwan sandstones, as described

under chapter II indicates that the sandstones have not

suffered much compaction during burial and their original

texture and fabric has not been modified to any appreciable

extent by the process of compaction.

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CHAPTER IV

PETROFACIES AND PROVENANCE INTERPRETATION

The word "Provenance" has been derived from French

word 'provenier' and Latin word 'Proveniens' meaning origin

or place where produced. In sedimentary petrology provenance

refers to the identify and composition of source rocks,

relief and climate in source area, and to some extent

includes transportation factors (Suttner, 1974). During the

last two decades sedimentologist v/orking on problems of

detrital composition and provenance of sedimentary rocks

have increasingly realised that the key relations between

provenance and basin are governed by plate tectonics, which

thus ultimately controls the distribution of different types

of sandstone (Dickinson and Suczek, 1979). The studies

attempting to interprete detrital modes of sandstones to

plate tectonic settings have led to the recognition and

discription of "Petrofacies" in sedimentary sequences. The

term 'petrofacies is employed for those facies which can be

distinguished principally by their composition and

appearance.

Krynine (1942) interpreted mineral composition in

terms of the geosynclinal cycles, which effected rates of

the source area uplift and basin subsidence and controlled

the geological composition of source terranes. Middleton

(1960) similarly concluded by using chemical composition of

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sandstones. Many ideas and conclusions of Krynine and

Middleton have been adapted to plate tectonic theory.

To interpret detrital mineral and chemical

composition in terms of plate tectonism, attempts were made

by several workers, which included Dickinson (1970; 1985),

Dickinson and Rich (1972), Crook (1974), Schwab (1975),

Dickinson and Suczek (1979), Valloni and Maynard (1981).

Petrofacies studies help in interpreting the

tectonic setting for ancient detrital sequences. The

appearance of a particular mineral assemblage may indicate

an important tectonic event such as uplift and erosion of

an arc, plutonic suite or an ophiolites assemblages along a

suture and this may help to date the time of intrusion or of

continental collision (Ingersoll, 1978; Eisbacher, 1981;

Schwab, 1981).

The use of quantitative detrital modes, calculated

from point counts of thin section, to infer sandstone

provenance is now well established (Dickinson, 1985). The

detrital modes of sandstone primarily reflect the different

tectonic setting of the provenance but various other factors

which effect sandstone composition are relief, climate,

transport mechanism, depositional environment and diagenetic

change. Diagenetic changes are also secondary importrant

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factor which modify sandstones composition (Akhtar et al.

1992) .

In the present investigation, the detrital minerals

of the Wadhwan sandstones have been studied for the purpose

of petrographic classification of the sandstones and inter­

pretation of their provenance and plate tectonic setting.

The classification of sandstone is a shorthand

method of summarising important discriptive and/genetic

features of a particular rock. Sandstone classification has

been attempted by several authors. These classifications

have been reviewed by Klein (1963), McBride (1963), Okada

(1971) and Pettijohn et al (1972).

Folk's (1980) classification based on the

composition of detrital framework constituents is most

commonly used classification for the description and

comparison of sandstones. This classification was used in

the present study of the Wadhwan sandstones for a meaningful

comparison with other sandstones. The detrital framework

grains were grouped into three end members.

(i) all types of quartz including metaquartzite

(ii) all single feldspar grains plus granite and gneiss

fragments.

(iii) all other rock fragments (chert, slate, phyllite,

schist, volcanics, limestone,sandstone, shale).

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Q

Quar t z a r e n i f e

F i g . 18 : C l a s s i f i c a t i o n of t h e V7adhv/an sands tones (According t o t h e scheme of Folk, 1980) .

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The average composition of the framework grains of

the Wadhwan sandstones is 98.8% quartz, 1.0% rock fragments,

0.19 feldspar and other constituents. All the 36 sample

points plotted on the Folk's (1980) classification triangle

fall in the quartzrich end member designated Quartz arenite

(Fig. 18).

PETROFACIES

The classification based on Dickinson's (1985)

scheme puts emphasis on tectonic setting of the provenance

which primarily controls the sandstone composition. The

other secondary factors (relief, climate, transport

mechanism, depositional environment, diagenesis) also play

their roles in determining sandstone composition. The roles

of these factors in influencing the detrital composition

of the Wadhwan sandstones have been discussed earlier in

chapter III of this dissertation.

In accordance with Dickinson's (1985) scheme the

detrital modes of the Wadhwan sandstones were identified and

recalculated to 100 percent as the sum of Qm, Qp, P,K, Lv

and Ls (Table 10). The sandstones donot contain intrabsinal

grains ( Zuf f i, 1980).

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Table 10: Classification and symbols of grain types (after

Dickinson 1985)

A. Quartzose Grain (Qt = Qm + Qp)

Qt = Total quartz grain

Qm = Monocrystalline quartz

Qp = Polycrystalline quartz

B. Feldspar Grain (F = P + K)

F = Total feldspar grains

P = Plagioclase grains

K = K-Feldspar grains

C. Unstable lithic fragments (L = Lv + Ls)

L = Total unstable lithic fragments

Lv = Volcanic/metavolcanic lithic fragments

Ls = Sedimentary/metasedimentarylithic fragments

D. Total lithic fragments (Lt = L + Qp)

Le = Extrabasinal detrital lime clasts

(not included in L or Lt)

Two complementary triangular diagrams (Fig.l9A/B)/

each of which involves a different set of grain populations,

were employed for the analysis of the data on detrital modes

of the Wadhwan sandstones. These diagrams i.e. Qt-F-L and

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RECYCLED OROGEN PROVENANCES

CONTINENTAL BLOCK PROVENANCES WITH SOURCES ON STABLE CRATONS

(C) AND IN UPLIFTED BASEMENT(B)

DECREASING MATURITY OR STABILITY

INCREASING RATIO OF OCEANIC TO COTINENTAL MATERIALS

72

CONTINENTAL BLOCK PROVENANCE

MERGER OF FIELDS FOR MATURE ROCKS WITH STABLE FRAME WORKS

RECYCLED OROGEN PROVENANCES

INCREASING RATIO OF CHERT TO QUARTZ

MERGER OF FIELDS FOR BASEMENT AND ARC / INCREASING RATIO ROOTS / OF PLUTON(C(PJ TO

Fig . 19: Classificaticxi of the VJacahv/an sandstone (Based on the Gcherr? of Dickincon, 1985).

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Qm-F-Lt plots, presented by Dickinson (1985) represent

actual reported distribution of mean detrital modes for

sandstone suites derived from different types of provenances

plotted on standard triangular diagrams. The two diagrams

both show full grain population, but with different

emphasis. The Qt-F-L plot where all quartzose grains are

plotted together puts emphasis on grain stability, and thus

on weathering, provenance, relief, and transport mechanism

as-well-as source rocks. In the Qm-F-Lt plot where all

lithic fragments are grouped together, the emphasis is

shifted toward the grain size of the source rock, because

finer grain rocks yield more lithic fragments in the sand

size range (Dickinson and Suczek, 1979).

Detrital modes of the Wadhwan sandstones calculated

according to Dickinson's (1985) classification scheme are

described below and their percentages are shown in Table 11.

Qm(monocrystalline quartz) is the dominant detrital

mode and form 79 to 98 percent in various samples,

averaging 91.6 percent. Qm grains are mostly subrounded.

Qp (polycrystalline quartz) includes recrystallized

metamorphic quartz and stretched" metamorphic quartz. Qp

ranges from 2.0 to 21.0 percent in various samples,

averaging 7.1 percent.

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Table 11: Percentage of framework modes of the Wadhwan

sandstones (based on the classification scheme- of

Dickinson, 1985)

Sample IIo.

02 03 04 09 10 12 13 14 15 16 17 18 20 21 22 23 24 25 29 30 31 32 33 34 36 39 41 42 43 44 45 46 47 49 50 55

Qt

99 100 98 100 98 99 98 98 97 99

100 98 100 99 99 99

100 100 100 99 99 98 99 99 99 98 99 99 99 98 98 99 96 98

100 99

F

0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 1 0 0 0 1 0 2 0 0 0

L

1 0 2 0 2 1 1 2 3 1 0 2 0 1 1 1 0 0 0 1 1 2 1 1 1 0 0 1 1 2 1 1 2 2 0 1

Qm

95 98 91 90 86 84 91 83 83 93 90 90 97 84 96 96 89 89 97 95 96 91 97 93 96 77 92 92 92 96 90 95 93 95 92 94

F

0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 1 0 0 0 1 0 2 0 0 0

Lt

5 2 9

IS) 14 16 8

17 17 7

10 10 3

16 4 4

11 11 3 5 4 9 3 7 4 21 7 8 8 4 9 5 5 5 8 6

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K-feldspar grains are not conunon in the Wadhwan

sandstones and were observed in very fevi? samples. The.

feldspar grains consist of weathered orthoclase and their

percentages range from 1.0 to 2.0 percent in the few

samples in which the grains occur. The feldspar grains

average about 0.19%.

Ls (rock fragments) comprises 1.0 to 3.0 percent of

the detrital fraction. They include metasedimentary/

sedimentary lithic fragments of phyllite, quartzite, chert/

sandstone and siltstone etc.

PLATE TECTONIC SETTING

On the standard Qt-F-L plot, the studied samples lie

in the continental block provenances with sources on stable

cratons because most of the points fall near the Qt pole

(Fig. 19A). On the Qm-F-Lt plot most points lie in the

transition zone between the fields of continental block

provenances and recycled orogen provenances. The points are

mostly located on the Qm-Lt leg of the triangular diagram

(Fig. 19B).

The continental blocks are tectonically consolidated

regions which represent amalgamated ancient erogenic belts

that have been eroded to their deep seated roots and lack

any relict genetic relief (Dickinson, 1985). Detritus from

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nonorogenic continental block forms a spectrum of sand types

derived from the broad positive areas of stable cratons at

one extreme and from locally uplifted, commonly fault-

bounded basement block at the other extreme.

The petrofacies analysis of the Wadhwan sandstones

suggest their sources on stable craton (Fig. 19A). The main

sources for craton-derived quartzose sands are low-lying

granitic and gneissic exposures, supplemented by recycling

of associated flat lying platform sediments. It has been

mentioned elsewhere that the source rocks of the Wadhwan

sandstones, located northeast of the study area, consisted

of Precambrian metasediments and granite-gneisses of Delhi

and Aravalli Supergroup.

The location of the study area within a humid

tropical belt during the lower Cretaceous (Thompson and

Barron,1981) and the prevailing warm and humid climate must

have affected the weathering pattern of the source rocks. An

intense chemical weathering possibly destroyed most

feldspars and labile constituents. Therefore the continental

block provenance that provided detritus to the study area

during the deposition of the Wadhwan sandstones was deeply

weathered.

The formation of mature quartzose sands/ such as

those of the Wadhwan sandstones, have been ascribed to

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multicyclic reworking on cratons by several workers. However

recent work has shown conclusively that quartzose sand is

also being produced as first-cycle sediment from deeply

weathered granite and gneissic bed rock exposed in tropical

low lands of the modern Amazon basin (Franzinelli and

Potter, 1983). In view of the intense and deep weathering

envisaged for the source rocks of the Wadhwan sandstones/

recycling was perhaps not an important factor in the

formation of quartzrich Wadhwan sandstones.

The development of first cycle quartzrich sand

requires low relief in the provenance to allow prolonged

weathering. This is demonstrated by quartz-poor nature of

both fluvial and littoral Holocene sands derived from

drainage basins in tropical highlands with high relief

(Ruxton, 1970). Thus, even where the climatic potential for

intense weathering exist, quartz rich sands will not be

produced unless the relief is low. It follows therefore that

a low relief marked the continental block provenance from

where the Wadhwan sandstones were derived.

A large majority of the Wadhwan sandstones are

texturally submature, that is, they contain under 5% clay

but detrital grains are poorly sorted and not well rounded.

This indicates that the Wadhwan sandstones were mostly

deposited in environments rather protected^£^lSHF^S*=at^tence

~Dsa.zLv3 \\-^'

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78

wave and current action. This seems quite likely as the

Wadhwan Formation represents localised deposition in

estuaries and embayments (Casshyap and Aslam, 1992). The

waves and currents had sufficient strength to winnow away

the mud, but were not strong enough to bring about sorting

and rounding of the detrital grains.

The detrital grains of the Wadhwan sandstones are in

the sand-size range and are believed to be transported from

a distance of a few hundred kilometers, considering the

location of the Aravalli highlands with respect to the study

area. This distance of transportation is not sufficient to

bring about rounding and sorting of detrital grains within

the sandsize range exhibited by the Wadhwan sandstones.

It is now a well established fact that the lower

Cretaceous sedimentary rocks of Saurashtra were deposited in

faulted troughs (Biswas, 1982). A recent study of these

sediments, specially their facies, helped in constructing

their tectono-sedimentary model (Casshyap and Aslam 1992).

The Lower Cretaceous sedimentary rocks including the Wadhwan

Formation of Saurashtra basin were deposited in a failed

rift. The development and infilling of the Lower Cretaceous

Saurashtra failed rift was concomittent with the

pericratonic rifting and opening of the Arabian sea to the

west.

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79

Fault-bounded basement uplifts along incipient rift

belts within continental blocks shed arkosic sands mainly

into adjacent linear troughs (Dickinson, 1985; Dickinson and

Suczek, 19 79). These authors have demonstrated that in such

a tectonic setting, a spectrum of lithic-poor quartzo-

feldspathic sands forms a roughly linear array on Qt-F-L and

Qm-F-Lt plots linking these arkosic sands with the craton-

derived quartzose sands that plot near the Qt and Qm poles.

However the Qm-F-Lt plot of Wadhwan sandstones (Fig. 19B)

shows that the points are mostly located on the Qm-Lt leg of

the diagram and lie in the transition zone between the

fields of continental block provenances and recycled orogen

provenances. The basement uplifts may shed sands having

affinity with detritus derived from recycled orogens

provided erosion has been insufficient to remove cover rocks

from basement (Mack, 1984). This may explain the false

signatures of recycled orogen provenance in the case of the

Wadhwan sandstones.

From the foregoing discussion, we can now construct

a plate-tectonic model for the tectonic setting of the Lower

Cretaceous Saurashtra basin during the deposition of the

Wadhwan sandstones. An incipient rift developed within the

Precambrian Aravalli continental block. The metasedimentary

and granite rocks of the Aravalli craton were deeply

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weathered under the warm and humid climate during Lower

Cretaceous. Thus most of the labile constituents of the

source rocks v/ere destroyed by weathering, and quartzrich

detritus was shed into the Saurashtra rift. The relief of

the provenance was low and erosion processes were not strong

enough to remove the cover rocks from the basement.

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CHAPTER V

SUMMARY AND CONCLUSIONS

Several prominent rift basins including the

Saurashtra basin developed in Western India at different

stages of evolution of the Indian subcontinent duing

Mesozoic. The Saurashtra basin developed in Early Cretaceous

conciding with uplift of northern Jurassic basin. The Kutch

and Saurashtra basins represent parts of an elongated

extensional trough where up and down rifting during

Jurassic-Cretaceous time brought about basin formation and

sedimentation, first in northern part (Jurassic of Kutch) and

latter in southern part (Early Cretaceous of Saurashtra).

The Early Cretaceous (Upper Tethonian to Albian:

145-97 m.y.) sedimentary rocks which are exposed in the

northeastern part of the Saurashtra basin comprise two

formations: Dharangadhra Formation (500m thick) and V7adhwan

Formation (50m thick) which are unconformably overlain by

the Deccan Traps of Late Cretaceous age.

The present study of the sandstones of Wadhwan

Formation (Early Cretaceous) of Surendranagar area mainly

aims to reconstruct their provenance and plate tectonic

setting of their deposition on the basis of petrofacies

study. A critical study of various factors influencing

detrital mineralogy of the sandstones and their provenance

interpretation has also been made.

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The field work was carried out for the purpose of

the collection of sandstone samples from different quarries

located around the Surendranagar town. Thin sections were

made from these samples and 36 sandstone samples showing

undisturbed fabric were selected for petrographic study.

The textural attributes of the Wadhwan sandstones,

such as size, roundness, sphericity and textural maturity

were studied with a view to interpreting the provenance of

the sandstones, and estimating the influence of texture on

the detrital modes and petrofacies. Interrelationship of

various textural attributes of the Wadhwan sandstones were

studied with the help of bivariant plots.

Statistical parameters of grain size of the Wadhwan

sandstones were computed with the help of cumulative

frequency curves and formulae according to the method of

Folk (1980). The sandstones are mostly medium grained (78%),

some fine grained (19%) and very few coarse grained (3%).

Their M ranges from 0.88 0 to 2.65 jz$. The Wadhwan

sandstone^ are generally moderately sorted (61%) to poorly

sorted (33%) and occasionally moderately well sorted (6%),

their O", values ranging from 0.62 to 1.53 s6. The sandstones

are mostly strongly fine to fine-skewed (64%) and mesokurtic

(50%). Their SK^ values range from -0.01 to 1.0 and. K^

values from 0.70 to 1.5.

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In various samples of the Wadhwan sandstones,

roundness of grains range generally from subangular to

subrounded. The mean roundness of individual samples ranges

from 0.32 to 0.41. According to their mean roundness the

individual samples are almost equally divided among

subrouned class (17 samples) and subangular class (19

samples). The aggregate data on grain roundness shows a

unimodal distribution with subrounded as the modal class.

The detrital grains of the Wadhwan sandstones are

mainly of low sphericity. Their mean sphericity values range

from 0.38 to 0.56 in various samples.

According to their textural attributes sandstones of

the Wadhwan Formation are mostly submature (80%), few are

mature (17%) and very few immature (3%).

Bivariant plots of various textural parameters, such

as mean size versus roundness, mean size versus sphericity,

mean size versus sorting, sorting versus sphericity and

sorting versus roundness show generally weak relationship.

However sorting versus sphericity plot shows a medium

relationship.

A study of grain to grain contacts of the Wadhwan

sandstones provided an idea about the degree of compaction

to which they were subjected. The average percentages of

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84

various types of grain contacts in the sandstones are;

floating, 7.9 percent; point, 60.25 percent; long, 24.50

percent; concavo-convex and sutured contacts, 7.3 percent.

Abudance of floating and point contacts suggest that the

Wadhv/an sandstones have suffered little compaction and

therefore their original texture and packing are largely

preserved.

Detrital composition of the Wadhwan sandstones was

evaluated both quantitatively and qualitatively for the

purpose of (i) petrographic classification of the

sandstones and (ii) for the interpretation of their

provenance. Detrital quartz is the predominant constituent

and all the sandstones examined are quartzarenites. The

average composition of the sandstones is quartz, 98.3%; rock

fragments, 1.0%; feldspars, 0.19% and other minor

constituents (mica and heavy minerals etc), 0.57%. Among the

detrital quartz, the quartz of igneous origin (both common

and vein quartz) predominate which forms 91.0% of total

detrital quartz. The remaining grains of quartz belong to

recrystallized metamorphic quartz and stretched metamorphic

quartz. Rock fragments averaging 1.0% include chert and lov/

rank metamorphic rocks. Feldspars are not common and occur in

some samples. Feldspars average 0.19 percent. The feldspar

grains belongs to mainly orthoclase which arc weathered. The

other minor constituents are mica and heavy minerals.

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85

Muscovite is more common than biotite. Opaques, tourmaline

and zircon are the main types of heavy minerals.

The clay matrix, averaging 1.6 percent, comprises

mainly kaolinite. The clay minerals appear to be both

allogenic and authigenic as indicated by their crystal habit

and morphology observed under SEM. Allogenic kaolinite was

derived by intense weathering of granites and gneisses in

the provenance, while the authigenic clay is the product of

diagenesis.

The cementing materials in the Wadhwan sandstones

are iron oxide, silica, and carbonate. The iron cement

occurs in the form of coatings around the detrital grains as

well as patches, which show replacement and corrosion of

detrital grains. The silica cement occurs in the form of

overgrowth on detrital quartz grains. The calcite cement

occuring in very few samples shov/s patchy distribution and

has corroded quartz grains.

A critical analysis of the various factors

influencing the detrital mineralogy of the Wadhwan

sandstones and hence the provenance and petrofacies

interpretation was carried out to arrive at a meaningful

conclusion. The various factors examined included

paleogeography, source rock composition, distance of

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86

transport, paleoclimate, depositional environments and

diagenetic modifications.

The paleogeographic reconstruction of the Saurashtra

rift suggests that the provenance of the sandstones was

located tov/ards northeast/ in the Aravalli highlands, a few

hundred kilometer from the study area. The Precambrian rocks

of Delhi and Aravalli Supergroups identified as the

provenance of the sandstones consist of mainly quartzites

and phyllites which are intruded by granites. Detrital

mineralogy of the Wadhwan sandstones matches the composition

of the identified source rocks. The sandstones were mainly

derived from metasedimentary rocks and granite-gneisses.

The Lower Cretaceous period was marked by warm and

humid climate in the study area which was responsible for

rigorous weathering of the Precambrian basement rocks in the

provenance resulting in destruction of much of the feldspars

and labile constituents. Paleoclimate was therefore a

leading factor in the formation of highly quartzose

sandstones of the Wadhwan Formation.

The sandstones are mainly texturally submature

because they were deposited in rather protected environments

of estuaries and embayments• The compositional maturity of

the sandstones is not the result of depositional reworking,

as the sandstones do not show a comparable degree of

textural maturity.

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Diagenetic processes such as dissolution/

replacement and compaction have brought about little

modification of the original detrital constituents.

Dissolution of feldspars has created about 2.0 percent of

secondary porosity. The replacement of quartz grain by iron

oxide and carbonate cements is only partial and localized.

The grain to grain contacts of the sandstones indicate very

little compaction.

The plate-tectonic setting and provenance of the

sandstones were interpreted with the help of Dickinson's

(1985) method of recognizing detrital modes and plotting

them on Qt-F-L and Qm-F-Lt triangular diagrames. The

detrital modes recognized and their average percentages are:

Qm (91.6%) Qp (7.1%); K-feldspar (0.19%) and Ls (1.0%). The

petrofacies analysis of the sandstones suggest continental

block provenances with source on stable craton which has

been recognized as the Aravalli craton. The continental

block provenance that supplied detritus to the Saurashtra

rift was, deeply weathered. A low relief marked the

continental block provenance permitting detritus a long

residence time in soil. The fault-bounded basement uplifts

along incipient rift belts within continental block are

known to shed arkosic sands into adjacent linear troughs,

but quartz-rich detritus was deposited into the Saurashtra

rift because of v/arm and humid climate, low relief and long

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residence time in soil. The false signature of recycled

orogen provenance in the case of Wadhwan sandstones may be

attributed to insufficient erosion that failed to remove

cover rocks from the basement.

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100

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Page 110: PROVENANCE AND CLASTIC PETROFACIE9 OF WADHWAN …ir.amu.ac.in/7229/1/DS 2243.pdfother parts of Gondwanaland during Jurassic-Cretaceous time also invaded parts of the western margin

APPENDICES

Page 111: PROVENANCE AND CLASTIC PETROFACIE9 OF WADHWAN …ir.amu.ac.in/7229/1/DS 2243.pdfother parts of Gondwanaland during Jurassic-Cretaceous time also invaded parts of the western margin

KAR.RCSI7

• NAME OF sssssrsssss

X S S S 3 S S S X S S S

1 . 5 5 0 1 . 5 0 0 1 . 7 0 0 1 , 9 0 0 1 . 6 0 0 0 . 8 8 0 1 . 9 3 0 1 . 6 6 0 1 , 4 0 0 1 . 6 5 0 1 , 5 0 0 1 , 8 0 0 1 . 5 0 0 1 . 4 5 0 1 . 6 0 0 2 . 1 9 0 1 . 1 5 0 1 . 7 0 0 2 . 0 5 0 1 , 6 0 0 2 . 6 5 0 1 . 6 6 0 2 . 4 8 0 1 . 9 8 0 1 . 8 6 0 1 . 1 6 0 1 . 2 6 0 1 . 6 0 0 1 . 8 1 0 1 . 8 6 0 1 . 4 8 0 2I08O 1,530 2.150 1.700

sBBsaasrssss 61.

Z S S 8 S S S S X 3 S S

BLOCK =

Y

'.»

SIZE Vs

27-MAY-1093

R0UNDNEv*5S ;rsrssrsss = r:

• ij t *

.380

.370

.400

.380

.390

.370 ,360 .410 .360 .340 .350 .330 .370 .350 .330 .380 .350 .350 .380 . tHO .3«0 .360 .3*»0 .340 .340 .320 .370 .380 .370 .350 .3 50 .390 .360 .360 .320 .360

xssssssas 660 ssssssssx

0, 0, 0. 0, 0, 0, 0, 0, 0, 0. 0, 0. 0. 0, 0,

0, 0, 0, 0, 0. 0, 0, 0, 0, 0. 0, 0. 0. 0.

0, 0. 0, 0, 0,

S s S

sas

Dx . 0 . 1 6 3 . 0 . 2 1 3 . 0 . 0 1 3 0 . 1 8 7 :S:JH 0 . 2 1 7

' 0 . 3 1 3 '0 • 06 3 '0 ,21 ' 0 , 0 8 ^ 0 . 2 1 3 0 , 2 6 3 VM= . 0 . 5 6 1 •O.Ol i 0 . 3 3 7

• 0 . 1 1 3 0 .Q3^

. 0 . 0 5 3 0 . 7 6 7 0 . 2 6 7 0 . 1 4 7

• 0 . 5 5 3 0 . 4 5 3 0 . 1 1 3 0 . 0 9 7 0 . 1 4 7 0 . 2 3 3 o'Ali 0 , 1 8 3 0 , 4 3 7 0 . 0 1 3

Dv 0 . 0 1 7 0 . 0 0 7 0 . 0 3 7 0 . 0 1 7 0 . 0 2 7 0 . 0 0 7

- 0 . 0 0 3 0 . 0 4 7

- 0 . 0 0 3 - 0 . 0 2 3 - 0 . 0 1 3 - 0 . 0 3 3

0 . 0 0 7 - 0 . 0 1 3 - 0 . 0 3 3

0 , 0 1 7 - 0 , 0 1 3 - 0 , 0 1 3

0 , 0 1 7 0 . 0 1 7 0 . 0 1 7

- 0 . 0 0 3 0 . 0 2 7

- 0 . 0 2 3 - 0 . 0 2 3 - 0 . 0 4 3

0 . 0 0 7 0 . 0 1 7 0 . 0 0 7

- 0 . 0 1 3 - 0 . 0 1 3

0 . 0 2 7 - 0 . 0 0 3 - 0 . 0 0 3 - 0 . 0 4 3 - 0 . 0 0 3

DXS

0 , 0 2 6 0 . 0 4 5 0 . 0 0 0 0 , 0 3 5 0 . 0 1 3 0 , 6 9 4 0 , 0 4 7 0 , 0 0 3 0 , 0 9 8 0 . 0 0 4 0 . 0 4 5 0 , 0 0 8 0 , 0 4 5 0 , 0 6 9

0 . 2 1 8 0 , 3 1 7 0 , 0 0 0 0 . 1 1 4 0 . 8 7 8 0 . 0 0 3 0 , 5 8 9 0 , 0 7 1 0 , 0 2 2 0 , 3 0 6

0 , 0 1 3 0 . 0 0 9 0 . 0 2 2 0 , 0 5 4

oioli 0 , 0 0 0

1 3 , 0 7 0 0 , 0 0 0

rsasss Dy

:3sssa 0 0 0 0

0 0 0 0

rsaaaa Bsaass

ssssssxa S D saaasass .000 .000 ,001 ,000 ,001 ,000 ,000 .002 .000 .001 . 000 .001 .000 .000 .001 .000 .000 .000 .000 .000 .000 .001 .001 .001 .002 .000 .000 .000 .000 .000 .001 .000 .000 .002 .000 aaaaai

0,000 saaaasas

isaasaa: xDv aasssBi -0.003 -0.001 0.000 0.003

-0,003 -0.006

•5«50i -0.002 0.001 0.001

.?:SSl

0.016 0.000

-0!006 -0.003 0.024

-0,003 •0.002 0.001

-0.002 $.003

0.001 -0,019 0.000

asvaaaaaa:

r s 0,1925. Prcent«ne= 3,7o730 r Squar Or CoeffI*^rIentof determination a 0.16829 standard errors 1,14412

aasaaasssassssssassBssssassasssssaaaasaasaasasaaasaaaaaaaaaaaaaaaaaaaaaa: -1 to tl is ranac of r IF r < 0.3 the Correlation beween varlableg is weak, r 0,3 to 0,7 mertinm. r > 0,7 strono

Page 112: PROVENANCE AND CLASTIC PETROFACIE9 OF WADHWAN …ir.amu.ac.in/7229/1/DS 2243.pdfother parts of Gondwanaland during Jurassic-Cretaceous time also invaded parts of the western margin

'^ KAR.RES;10

NAMK -OF BLOCK = sssrsszssrss:==r:=s:

X Y S 8 X S S P S S 3 = S S S Z S S S S S :

27-MAy-l993 20:37 P«ae 1 SIZE VS SHAPE

Dx

1 . 5 5 0 1 . 5 0 0 1 . 7 0 0 1 . 9 0 0 1 . 6 0 0 0 . 8 8 0 1 . 9 3 0 1 . 6 6 0 1 . 4 0 0 1 . 6 5 0 1 . 5 0 0 1 . 8 0 0 1 . 5 0 0 1 . 4 5 0 1 . 6 0 0 2 . 1 8 0 1 . 1 5 0 1 . 7 0 0 2 . 0 5 0 1 . 6 0 0 2 . 6 5 0 1 . 6 6 0 2 . 4 8 0 1 . 9 8 0 1 . 8 6 0 1 . 1 6 0 1 . 2 6 0 1 . 6 0 0 1 . 8 1 0 1 . 8 6 0 1 . 4 8 0 2 . 1 0 0 2 . 0 9 0 1 . 5 3 0 2 . 1 5 0 liZ22-_

6? s B s r r s s r s s s

0 . S 6 0 0 , 5 6 0 0 , 5 5 0 0 . 4 4 0 0 , 4 7 0 0 , 4 5 0 0 , 4 1 0 0 . 3 8 0 0 . 4 6 0 0 . 4 1 0 0 , 4 1 0 0 , 4 0 0 0 , 4 1 0 0 , 4 1 0 0 . 4 4 0 0 , 4 5 0 0 . 4 7 0 0 . 4 4 0 0 , 4 ? 0 0 . 4 5 0 0 , 4 1 0 0 . 4 1 C 0 , 4 2 0 0 . 4 2 0 0 . 3 8 0 0 , 4 4 0 0 , 4 4 0 0 , 4 9 0 0 . 4 5 0 0 . 4 3 0 0 . 4 2 0 0 , 4 5 0 0 , 4 2 0 0 . 4 1 0 0 . 4 7 0 0 . 4 0 0

7660 s s s s s s s s s s s

- 0 . 1 6 3 - 0 . 2 1 3 - 0 , 0 1 3

0 , 1 8 7 - 0 . 1 1 3 - 0 , 8 3 3

0 . 2 1 7 - 0 . 0 5 3 - 0 . 3 1 3 - 0 . 0 6 3 - 0 . 2 1 3

0 . 0 8 7 - 0 . 2 1 3 - 0 . 2 6 3 - 0 , 1 1 3

0 . 4 6 7 - 0 . 5 6 3 - 0 , 0 1 3

0 , 3 3 7 - 0 , J 1 3

0 , 9 3 7 - 0 , 0 5 3

0 . 7 6 7 0 . 2 6 7 0 , 1 4 7

- 0 , 5 5 3 - 0 , 4 5 3 - 0 , 1 1 3

0 , 0 9 7 0 . 1 4 7

- 0 . 2 3 3 0 , 3 8 7 0 . 3 6 7

- 0 . 1 8 3 0 . 4 3 7

- o . o n TRTS

s s s s s s s

DV

0 0 0

• 0 0 0

• 0 • 0 0

• 0 . 0 •0 . 0 - 0 .0 0 0

. 0

. 0 0

-0 >0 • 0 • 0 •0 •0 •0 0 0

•0 • 0 0

• 0 • 0 0

• 0

,119 .119 ,109 ,001 .029 ,009 .031 .061 .019 ,031 ,031 ,041 ,031 ,031 ,001 ,009 ,029 001

DXS DyS DxDv : S S S S B B B S S S S 3 S S S S S S 3 S 3 S B 8 S S S S a S :

-0.021 0.009

001 ,031 ,021 ,021 ,061 ,001 ,001 ,049 ,009 .011 ,021 ,009 ,021 ,031 ,029 ,041

0,026 0.045 0.000 0,035 0.013 0.694 0.047 0.00 3 0.098 o.ooa 0.045 0.008

045 069 013

..218 0.317 0,000 0.114

013 878 003 589 071

,.022 0.306 0.205 0.013 0.009 0.022 0.054 0.150 0,135 0,033 0,191 0,000

0 .014 0 ,014 0 .012 0 .000 0 .001 0 .000 0 . 0 0 1 0 . 0 0 4 0 .000 0 .001 0 . 0 0 1 0 . 0 0 2 0 . 0 0 1 0 .001 0 . 0 0 0 0 . 0 0 0 O.OOl 0 .000 0 . 0 0 0 0 .000 0 .000 0 .001 0 .000 0 .000 0 . 0 0 4 0 .000 0 .000 0 .002 0 .000 0 . 0 0 0 0 .000 0 .000 0 .000 O.OOl

km

- 0 . 0 1 9 - 0 . 0 5 5 - 0 , 0 0 1

0 . 0 0 0 -0-002 - 0 . 0 0 7 - 0 . 0 0 7

0 . 0 0 3 - 0 , 0 0 6

0 .008 0 , 0 0 0 0 . 0 0 4

- 0 , 0 1 6 0 . 0 0 0

- 0 , 0 0 7 - 0 . 0 0 1 - 0 , 0 0 1

0 . 0 0 2 - 0 . 0 1 6 - 0 . 0 0 6 - 0 , 0 0 9

0 .001 0 , 0 0 1

- 0 , 0 0 6 -olSoi

0 , 0 0 5 0 .003

- 0 , 0 0 8 0 , 0 0 6 S:8i? B Z S S S S S S S S S S B S B B S B B S B S S B a a S S a S :

0,000 0,000 BBBssBSBSssBSBBsssassasaaaaaaa:

r = -O.J521 Prcentaoe= -2,3t280 * .,«.^ r Squar nr Coeffleclentof determination s 0.16950 standard errors -0,89720

iBsssBssBssssBsssBsssSBssssBSBSsBSBSsssssBssBsassaBsaBBBsaaaaaaaaaaaas •1 to 41 is r«nae of r - , ^. . IF r < 0.3 the correlation beween variables Is weak. r 0.3 to 0.7 mer'lijm. r > 0,7 . trono

Page 113: PROVENANCE AND CLASTIC PETROFACIE9 OF WADHWAN …ir.amu.ac.in/7229/1/DS 2243.pdfother parts of Gondwanaland during Jurassic-Cretaceous time also invaded parts of the western margin

KAR,RES;7

NAME OF asBrsrsssss

X aasrssBBSSs

1.120 0.720 l.OJO 0.890 1.000 1.050 0.930 0.800 0.760 1.000 0.790 0.900 l.llO 1.040 0.990 0.910 1.160 1,210 0.900 1.050 0,960 0.890 0.770 0,670 1,090 0,780 0.930 0.840 1,120 0,860 0,920 0.620 0.840 0,830 1,100 1.530

BLOCK s

Y sssssssss

0,380 0.370 0.400 0.380 0.390 0.370 0.360 0.410 0.360 0.340 0,350 0.330 0.370 0.350 0,330 0.380 0.350 0.350 0,380 0,380 0.380 0.360 0.390 0,340 0.340 0.320 0.370 0.380 0.370 0.350 0.350 0.390 0.360 0.360 0.320 0.360

BXBsatsaBSBsastfSBaass 34,

r :

.090

SORTING sss~S7Ssss—:

nx S S S S S S B S S S B :

0.173 -0.227 0.063 -0.057 0,053 0,103 -0.017 -0.147 -0,lfl7 0.053 -0.157 -0.047 0,163 0.093 0.043 -0.037 0.213 0.263 -0.047 0.103 0.013

-0.05^ -0.177 -0,277 0,143 -0,167 -0,017 -0.107 0.173 -0.087 -0.027 -0,327 -0.107 -0,117 0,153 0.583

sss—saBSSss: 13.070

s -0.1228 Prcentaqes 1 r Squar Or Coeff

,50716 ('•clentof d«

27-MAY-1993 20110

VS ROUNDNFSS SSSSSSSSZSSB

DV

0.017 0.007 0.037 0.017 0.027 0.007 -0.003 0.047

-0.003 -0.023 -0,013 -0.033 0.007 -0.013 -0,033 0.017

-0.013 -0.013 0,017 0.017 0,017

-0.003 0.027 -0.023 -0,023 -0,043 0.007 0.017 0.007

-0.013 -0.013 0.027

-0,003 -0.00 3 -0.043 -0.003

S B S S B B S B : DXS

0.030 0.052 0,004 0.003 0.003 o.on 0.000 0.022 0.035 0,003 0.025 0.002 0.027 0,009 0.002 0.001 0.045 0.069 0,002 0.011 0.000 0.003 "•921 0.077 0,020 0,028 0,000 0.011 0.030 0,008 8:?8; i-.m 0.023 0.340

rSSBBSSBBXBXBBBSaSSSa 0,000

zxssasssssBSBssssasas

'termtnatIon = 0.

Paae 1

:ssssssxsBBS9CBaasBs Dys

ESSSBBXBB 0.000 0.000 0.001 0.000 0,001 0.000 0.000 0,002 0.000 0,001 0.000 0.001 0.000 0.000 0,001 0.000 0,000 0.000 0,000 0,000 0,000 ?:88! 0,001 0,002 0,000 0,000 0,000 0,000 0.000 0.001 0.000 0,000 0,002 0,000

aasaaaaB 0.

w S B B B ^ i B S

17020

DxOv SSSSSBSBBBB

0,003 -o.oof .8:8Sf o.oo! 0.001 O.OOQ

-0.007 o.ooi -0.001 0.002 0.002 0.001 -0.001 -0.001

•oIooS -0.003

-S:8?i t'M

•8:S8I -8:8?? 0.000 -0,002 0.001

O.ooi 0.000 -0.009 0.000 0.000

-0.007 •0.002

mmmmmmMmmm* 000

standarfi «»rror* '^•^21^2 _ - -

-1 to *l Is ranae of r -IF r < 0 3 the correlation beween variables is weak, r 0,3 to 0.7 medium, r > 0,7 strona

SaSBSB8BBB:


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