SEDIMENTOLOGY OF THE GODAVARI DELTA AROUND RAZOLE, EAST QODAVARI

DISTRICT, ANDHRA PRADESH

\

A DISSERTATION StAmttted in partial fidfiUnaU of the requirementM

for the award tf the degree of

0iUSittt of $I|tlO£!op()P IN

GEOLOGY ^

BY

TADALA RAMABRAHMAM

DEPARTMENT OF GEOLOGY FACULTY OF SCIENCE

ALIGARH MUSUM UNIVERSITY ALIGARH (INDIA)

1994

BS2600

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7<f^

1 7 FEB ^''O

Ref. No.-

PHONE : (0571 ) 2 6 6 1 5 TELEX : 664-230-AMU-IN

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

/Geol. Dated 2 ^ /^- fU

CERTIFICATE

PROFESSOR B.D. BHARDHAJ

I certify that the. work presented in this dissertation

has been carried out by Mr. Tadala Ramabrahmam, under

my supervision. The work is an original one and has not

been submitted for any other degree at this or any

other University.

(B.D. Bhardwaj)

TO MY LOVING

SISTER & BROTHER-IN-LAW

ACKNOWLEDGEMENTS

I wish to express my deep sense of gratitude to my supervisor Prof. B.D. Bhardwaj for his support, guidance, constructive criticism and encouragement throughout the course of this study.

I wish to thank Prof. Iqbaluddin, Chairman Department of Geology, A.M.U. Aligarh and Director, Remote Sensing Application Centre for resource evaluation and geo-engineering, A.M.U., Aligarh for providing necessary facilities during the course of this research work.

I am thankful to Dr. Adal Singh, Mr. Md. Erf an Ali Mondal, Mr. Mohd. Asif and to Dr. A.H.M.Ahmad for all the help and cooperation I received from them during the course of this study.

A token of deep appreciation to B.T. Ashok and Syed Jalal Khundmiri for the guidance and kind help all through the course of my study as well as in the compilation of this dissertation.

I acknowledge the help and cooperation received from Mr. Adil Anwar, Mr. S.A. Rashid, Mr. Asad Umar, Mr. Haris Umar, Mr. Arif Khan and Mr. Uma Shankar.

I wish to express my heartfelt gratitude to Mrs. and Mr. Kodi Venkateswara Rao, Mr. Adinarayana who have always supported me in all my academic endeavours and showered their love on me.

Thanks are also due to Messrs Z.Husain, Salimuddin and A. Ali, Department of Geology A.M.U., Aligarh for library facilities, painstaking cartographic designs and prepartion of thin sections, respectively.

(TADALA RAMABRAHMAM) 111

CONTENTS

Page No.

CERTIFICATE

ACKNOWLEDGEMENTS

LIST OF FIGURES

LIST OF TABLES

LIST OF PLATES

11

111

VI

XI

Xll

CHAPTER - I INTRODUCTION

Location and Environs of the area

Godavari River

Geomorphological Setting

Methods of Investigation

Field Method

Laboratory Method

1

2

2

4

4

4

5

CHAPER - II FACIES DESCRIPTION 7

Trough Cross Bedded Sandy Facies (St) 9

Planar Cross Bedded Sandy Facies (Sp) 11

Horizontal Bedded Sandy Facies (Sh) 13

Ripple Cross Laminated Sandy Facies (Sr) 15

Parallel Laminated Fine Sandy Facies (Fl) 18

Lenticular Sandy Facies (Si) 18

Massive Silt and Mud Facies (Fm) 20

IV

CHAPTER - III DISTRIBUTION OF GRAIN SIZE IN RELATION TO

SEDIMENTARY STRUCTURE 22

General 22

Ripple Cross Laminated Sandy Facies (Sr) 27

Planar Cross Bedded Sandy Facies (Sp) 40

Trough Cross Bedded Sandy Facies (St) 43

Horizontal Bedded Sandy Facies (Sh) 44

Lenticular Sandy Facies (SI) 45

Parallel Laminated Fine Sandy Facies (Fl) 46

Massive Silt And Clay Facies (Fm) 46

Vertical Variation in Grain Size 49

CHAPTER - IV MINERAL COMPOSITION OF GODAVARI SEDIMENTS 52

CHAPTER - V FLOW PATTERNS

Vector Mean

Vector Strength

Variance

Interpretation

62

63

63

66

66

CHAPTER - VI DELTA MODEL 68

CHAPTER - VII CONCLUSION

REFERENCE

73

76

LIST OF FIGURES

Page No

Fig. - 1 Map of the study area and location of trenches. 3

Fig. - 2 Log probability plots of grain size distribution

in Trench No.l. 29

Fig. - 3 Log probability plots of grain size distribution

in Trench No. 2. 30

Fig. - 4 Vertical variation in facies in relation

to Mean size, S. deviation, Skewness and

Kurtosis in Trench No. 1. 31

Fig. - 5 Vertical variation in facies in relation

to Mean size, S. deviation, Skewness and

Kurtosis in Trench No. 2. 31

Fig.- 6 Log Probability plots of grain size distribution

in Trench No. 5. 32

Fig.- 7 Vertical variation in facies in relation

to Mean size, S. deviation, Skewness and

Kurtosis in Trench No. 5. 33

VI

Fig.- 8 Log probability plots of grain size

distribution in Trench No. 9. 34

Fig.- 9 Log probability plots of grain size

distribution in Trench No. 10. 35

Fig.-10 Vertical variation in facies in

relation to Mean size, S. deviation,

Skewness and Kurtosis in Trench No. 9. 36

Fig.-11 Vertical variation in facies in

relation to Mean size, S.deviation,

Skewness and Kurtosis in Trench No. 10. 36

Fig.-12 Log probability plots of grain size

distribution in Trench No. 3. 37

Fig.-13 Log probability plots of grain size

distribution in Trench No. 4. 38

Fig.-14 Vertical variation in facies in

relation to Mean size, S.deviation,

Skewness and Kurtosis in

Trench No. 3. 39

Fig.-15 Vertical variation in facies in

relation to Mean size, S.deviation,

Vll

Skewness and Kurtosis in

Trench No. 4. 39

Fig.-15 Log probability plots of grain size

distribution in Trench No. 6. 41

Fig.-17 Vertical variation in facies in

relation to Mean size, S.deviation,

Skewness and Kurtosis in

Trench No. 5. 42

Fig.-18 Log probability plots of grain size

distribution in Trench No. 8. 47

Fig.-19 Vertical variation in facies in

relation to Mean size, S.deviation,

Skewness and Kurtosis in

Trench No. 8. 48

Fig.-20 Log probability plots of grain size

distribution in Trench No. 7. 50

Fig.-21 Vertical variation in facies in

relation to Mean size, s.deviation,

Skewness and Kurtosis in Trench No. 7. 51

VILL

Fig.-22 • The mineral composition of

Godavari sediments in

Trench No. 1. 57

Fig.-23 The mineral composition

of Godavari sediments in

Trench No. 2. 57

Fig.-24 The mineral composition

of Godavari sediments in

Trench No. 3. 58

Fig.-25 The mineral composition

of Godavari sediments in

Trench No. 4. 58

Fig.-26 The mineral composition of

Godavari sediments in

Trench No. 5. . 59

Fig.-27 The mineral composition of

Godavari sediments in

Trench No. 6. 59

Fig.-28 The mineral composition of

Godavari sediments in

Trench No. 9. 60

IX

Fig.-29 The mineral composition of

Godavari sediments in

Trench No. 10. 60

Fig.-30 Average mineral composition

of Godavari sediments. 61

Fig.-31 Map showing variations in

flow direction from general

flow direction. 64

Fig.-32 Generalized secjuence of

Godavari river delta. 70

Fig.-33 Block diagram showing

bedforms and stratifcations

of the Godavari delta. 71

LIST OF TABLES

Page No.

TABLE - I Size Frequency Distribution

(percent) of Godavari River delta sand 24

TABLE - II Grain size characteristics of Godavari

River delta 25

TABLE - III Grain size parameters of sub-population in

individual sample 26

TABLE - IV Mineral composition of Godavari sediments 53

TABLE - V Com.putation of vector mean and vector

magnitude of cross bedding azimuth 65

XL

LIST OF PLATES

PLATE - I

Fig. 1-2

Photographs showing trough cross bedding

bounded by cross bedding

Page No.

10

PLATE - II

Fig. 1-2

Photographs showing large scale

and small scale planar cross bedding 12

PLATE - III

Fig. 1-2

PLATE - IV

Fig. 1-2

Photographs showing parallel laminations 14

Photographs showing ripple cross laminations 15

PLATE - V

Fig. 1-2

Photographs showing climbing

ripple laminations, small scale

ripples and massive mud 19

CHAPTER I

CHAPTER I

INTRODUCTION

The study of the modern sediments provide valuable

information regarding the process and products of the known

environments, this information can be of great help in the

interpretation of the ancient sequences.

Keeping this in view the recent past the attention of

sedimentologists have been attracted to the modern sediments

specially the river deposits because they are the principal

agencies which provide weathered material. These weathered

products form sedimentary sequences. Some part of the stream

load is deposited on the land, forming alluvial plains and

some part is extended towards the sea forming coastal plains

and delta.

In the present study an attempt has been made to study

the sedimentology of delta sediments of Godavari river

around Razole. The delta sediments offer excellent

opportunity for studying the modern delta environments. The

present investigation is an intigrated field study, facies

analysis, mineral composition, and flow pattern in a small

area with a view to identify various lithofacies and their

characteristic features.

LOCATION AND ENVIRONS OF THE AREA

The study area is approximately 50 sq. Km. It is

situated in East Godavari district, Andhra Pradesh (Figl).

By and large the major part of the area is covered by

alluvium.

GODAVARI RIVER

The Godavari river which attains a width of

considerable proportion about 4.8 Km. down stream of

Rajahmundry divides into two primary distributaries at

Dowlaiswaram. At Dowlaiswaram, the fluvial system of the

Godavari has been effected by a Dowlaiswaram Barrage. The

water in the resultant reservoir is distributed by an

extensive network of irrigational channels spread over the

vast deltaic plain.

The primary distributary flowing eastward is known as

the Goutami Godavari, where as the one flowing south is

known as the Vasishta Godavari. In the lower reaches each of

the above two primary distributaries subdivide into several

secondary distributaries. Each of these secondary

distributary channels empties itself into the Bay of Bengal

independently.

Fig. 1. Map of the study area and location of trenches.

GE0M0RPH0L06ICAL SETTING

The Godavari river is the second largest river in India

ranking next to the Ganges, rising in the Western Ghats at

"TRIAMBAK" at an altitude of 1067 meters above mean sea

level near Nasik. The Godavari flows for 900 miles before

emptying into the Bay of Bengal.

The water resources division of the U.S. Geological

Survey (1962) has included the Godavari river in the list of

the larger rivers in the world. The river runs across the

peninsular India from West to East, and on it's way to the

sea it is met by sixteen major tributaries.

The Godavari basin is roughly triangular in shape, the

major drainage trend of the rivers of the peninsular India

including the Godavari is towards the East and South east is

due to the uplift of the Western Ghats and slightly tilt of

the peninsular India mass to the east during the Mesozoic

age Krishnan (1983).

METHODS OF INVESTIGATION

Field Methods : The area under investigation was divided

into ten locations and the data were collected from both the

banks. The method employed in the investigation was to dig

trenches with the help of a showel and khurpa. The trenches

were made without proper orientation to expose the primary

sedimentary structures. The depth of the trenches varies

from location to location depending upon the height of the

sand deposits made by the river during it's flood period.

Generally, the depth of the trenches range between 1.5 to 2

meters and the length between 1 to 1.5 meters. After

digging, the walls of the trenches were smoothened with the

help of a knife. Then the trenches were left for drying by

exposing them to air current or sun light. When sediments

become dry, the stratifications and other sedimentary

structures were visible clearly. Vertical facies of

sedimentary sequence were examined in trenches both in

longitudinal and transverse sections parallel to flow and

sketches were drawn to scale to illustrate different

facies,their relationship, bedding type, texture and primary

sedimentary structures. In all over 30 samples from various

facies were collected vertically at suitable intervals from

each trench for laboratory investigation of grain size and

mineral compostion.

LABORATORY METHOD

The grain size analysis was carried out by sieving

samples at 4 2 scale of Wentworth using ASTM sieves of 22 cm

diameter, twenty five samples from different localities,

including three from over bank deposits. In each case 100

grams of sample were sieved for 15 minutes using Ro-tap

Sieve shaker and fractions from different sieves were

collected.

The weight percent frequency and cumulative weight

percentage were computed and cumulative weight frequency

curves were plotted for each trench. To determine the

sediment properties, statistical parameters of size

frequency distribution given by Folk and Ward (1957) and

Visher (1965,1969) were .computed.

The heavy minerals were extracted from eight samples.

The material falling in next to model class was taken for

heavy mineral analysis. The separation was done according to

the centrifuge method of Taylor (1933), using bromoform of

specific gravity of 2.89 as separating medium. The heavy

mineral crop was washed with alchohol, dried, weighed and

mounted permanently in canada balsom. The slides were

studied using a swift automatic point counter fitted to a

petrological microscope for mineral composition. Since the

opinion differed as to the total number of grains that

should be counted to obtain a reliable estimate of mineral

composition of the given samples Potter and Pettijohn

(1963). Successively 200, 300, 400 and 500 grains were

counted from randomly selected slides. It was found that

counting of 100 to 300 grains per slide was sufficient.

However 200 grains per slide were counted for determining

the total model composition of the sands.

CHAPTER II

CHAPTER II

FACIES DESCRIPTION

The term facies was introduced by Gressly in 1830.

Gressely and Prevost in (1638) recognised various

sedimentary facies on the basis of lithology in Jurassic in

Eastern France. De Raff et al, (1965) introduced common

usage of facies on the basis of lithology, structure and

organic aspects of cyclecal representation in a number of

facies.

During the last few decades fluvial sediments have been

extensively studied in known environments with special

reference to various sedimentary facies. (Mial, 1980;

Walker; 1980; Jackson; 1976; Middleton; 1978; Klovan; 1964;

Young, 1975).

These studies have been used to understand the ancient

sediments and the environments of deposition responsible for

their deposition . A single example of present day variation

in physiochemical and organic setting of sedimentation

illustrates facies in the stratigraphic record to define

the specific sedimentary environment.

In the present study an attempt has been made to

recognise facies on the basis of lithology, primary

sedimentary structures, particularly in the studies of

modern depositional environments.

Delta models have been discussed and developed by

Coleman and Wright, 1975; Galloway, 1975; Reading, 1978; and

Walker, 1976.

Three dimensonal facies models, was suggested by Allen

(1965) for meandring streams and braided streams of Donject

type was described by Mial (1977).

Willings and Rust (1969) and Doeglas (1962) described

the modern streams while Cant and Walker (1976), Killing

(1968), and Steel (1974) described models from the ancient

sediments.

Mial (1985) proposed a classification based on eight

architectural elements for the fluvial sediments. The facies

code consist of two parts in that prefix indicate dominant

lithology and a suffix for sedimentary structure in each

facies.

In the present study seven different facies were

recognised in the vertical sections in the trenches on the

basis of grain size, bedding type and sedimentary

structures. The facies recognised were coded individually

following Mial (1985).

COARSE TO MEDIUM SANDY FACIES

1 Trough crossbedded sandy facies,(St)

2 Planar cross bedded sandy facies, (Sp)

3 Ripple cross-laminated sandy facies, (Sr)

4 Horizontal bedded sandy facies, (Sh)

8

FINE GRAINED FACIES

5. Parallel laminated fine sandy facies, (Fl).

6. Lenticular sandy facies, (SI)

7. Massive silt and clay facies, (Fm).

COARSE TO MEDIUM SAND FACIES

Trough cross bedded sandy facies (St): Trough cross bedded

facies occurs interbedded with planar cross bedded facies,

plate I (Fig.l & 2). The individual units range in thickness

from 8 to 50 cm. ( > 4 cm. thick, Reineck and Singh 1980).

Large scale stratification are abundant. In vertical

sections parallel to current flow, troughs are well

depicted by scours and in these sections traces of foresets

are commonly symmetrically curved and tangential to the

underlying erosional surfaces plate I(Fig.l & 2). In most

trenches foreset angle is about 141 and the scale of cross

bedding is about 25 to 50 cm. The large scale cross

stratification in lower part of the sequence comprises

coarse sand. The average grain size of the facies is

decreasing in the down stream. The formation of cross

bedding is controlled by current velocity, flow

characteristics and the rate of sediment supply. The large

scale cross bedding (>4 cm) occuring in Cosets, are formed

by the down stream migration of a symmetrical mega ripples,

dunes and sand waves Allen (1962 ; 1963) Jopling (1963).

PLATE - I

Jig.l. Showing trough cross bedding bounded by planar cross bedding.

Pig.2. Showing trough cross bedding and horizontal bedding.

10

Mckee (1957b), Lahee (1952) suggested that scour and filling

are responsible for the formation of trough cross bedding.

Scour filling is due to down stream migration of ripples.

Cosets of trough cross stratification indicate

unidirectional flow with appropriate range of water depth

and velocity to form three dimensional large ripples,

Singh, I.B. (1977); Reineck and Singh, (1986), Large scale

cross stratification can be formed by infilling of scour

pockets related to migrating the lee face of advancing

dunes, Jopling (1963).

According to Harms et al (1963), the mechanism of

scouring and infilling of the scour pockets develop a

tangential variety of stratification due to velocity and

high depth ratio.

The periodic occurance of fine grained material within

the sets, with truncational characteristics and tangential

contacts suggest a temporary, periodic increase in current

velocity, resulting in an increased supply of suspended

material. Discontinuties within the large scale cross

stratification may be related to grain size variation

during transportation. Jopling (1963).

Planar cross bedded sandy fades (Sp): Planar cross beds as

large in solitary sets and cosets plate II(Fig.l & 2). The

mean thickness of sets decreases vertically from 85 to 19

cm, from bottom to top of the sequence in most of trenches.

11

PLATE - II

Pig.l. Showing large scale cross "bedding.

Pig.2. Showing smt*ll scale planar cross bedding.

In channel sand bodies of this facies, the overlying and

underlying surfaces are erosional. The large planar cross

stratification units thickness range from 26 to 75 cm, these

planar cross stratifications were also observed to be

inclined normally in the current direction.

According to Harms et. al, (1982) planar cross

stratification may be deposited by migrating two dimensional

large ripples. Allen (1963) concluded that cosets of planar

cross beds are formed by migration of a symmetrical ripple

having straight and parallel crets and the scale of strata

is grouped on the basis of amplitude of the ripples.

Planar cross stratification are alphatype (Allen,

1963). They are sharp at scoured bases and tops, set

thickness ranges from 5 cm to 5 m, grain size and sorting

characteristics are similar to St facies Mial (1977). The

more common planar cross bedding consist > 30 cm thick units

and the bounding surfaces of the set laminae become

tangential. A cross bedding surface more or less common is

called planar cross bedding Reineck and Singh (1986).

Horizontally bedded sandy facies (Sh)

Horizontally bedded sandy facies show inclination less

than 4 degrees plate III(Fig. 1 & 2). The thickness

increases laterally, colour of this facies is grey and the

grain size is fine to coarse. Individual beds are generally

13

PLATE - I I I

1

P i g . l . Showing r ) a r a l l e l l a m i n a t i o n s i n medium sand .

equal to subequal in thickness and locally contain

lenticular bedding. The Sh facies displays mica flakes along

its laminae. The bedding surfaces are generally devoid of

ripple marks, indicating deposition by relatively high

velocity flow regime.

Bridge, (1978) described the origin of horizontal

bedding under turbulent boundary layers. The formation of

horizontal laminated facies can also take place under two

different conditions, ie. in shallow water and during flood

stage Mial 1977. The deposition may be attributed to an

increase in flow regime due to local shallowing of the basin

floor and seasonal increase in discharge or to sheet like

flood (McKee et al. , (1961). Horizontal stratification

consist of coarse sand may be interpreted as indicating

transportation in planar sheets under high energy

conditions Casshyap and Kumar (1987), Desloges and Church,

(1987). According to Coleman (1969), horizontal

stratification are formed by rapidly migrating trains of

exceptionally small bed forms.

Ripple cross laminated sandy facies (Sr) :

The ripple cross laminated facies consist of coarse

sand and thick beds, plate IV(Fig.l & 2). The thickness of

this facies ranges from 20 to 60 cm. The thickness

decreases vertically. In most of the trenches, Sr facies

15

PLATE - IV

Pig.l. Showing ripple cross laminati stratification. ons au base and planar

Fig, 2, SJiowxii^ ripiol e cross laminat ions and trough cross bedding,

16

overlain by trough cross stratification. The crest of the

laminae are inclined in the direction of current flow. The

angle of inclination ranges from 8| to 201. Individual

units may have perhaps deposited by waning flood.

Ripple cross laminations are developed, when the excess

suspended sediment is continuously available for deposition

which is deposited above the earlier formed rippled layer

Reineck (1963), McKee (1965), Singh and Kumar (1974). The

ripple cross laminations in which laminae is in phase are

interpreted, as the result of abundant supply of sediment

in suspension , no erosion on stoss side takes place and

laminae is in phase are completely, buried and preserved.

The ripple laminae is in phase are produced only when angle

of climb is greater than the stoss side slope. The ripple

cross lamination marked with high angle of climb, indicates

high rate of deposition which may have resulted from

deceleration of flow, with a corresponding increase in

sedimentation as occurs during waning stage of floods

Lindholm (1987).

Climbing ripples may be produced by straight crest,

undulatory or small linguoid current ripple or even by wave

ripples Reineck and Singh (1986).

17

FINE GRAINED FACIES

Parallel laminated fine sandy facies (Fl) : Parallel

laminated structures are sets of laminae in which individual

laminations are parallel to the lower set boundary Harms

and Fahnestock (1965). The structure is commonly observed in

fine sand and silt. The laminations show alternating dark

and light colour bends. The thickness of the laminae ranges

from 1 to 1.5 cm. The laminations do not show any kind of

undulations. This structure is mostly observed in over bank

deposits plate V (Figl).

Parallel laminations are developed in fine sand and

silt. The fine sand parallel laminations is formed when the

flow velocity is high and water depth is shallow under

upper flow regime. When such conditions exist the ripples

and dunes are destroyed, in such conditions water surface

is smooth like glassy appearance (Collenson and Thomson

1982).

Lenticular sandy facies (SI) : This facies is marked by the

presence of ripples, and well developed in bank deposits.

The thickness of the set comprising the laminations of

silt and clay ranges from 10 cm to 25 cm. Each laminae mud

is about 4 cm thick. The height of the ripple ranges from

1.5 cm to 3 cm and length of the ripple varies from 15 cm

to 20 cm.

18

PLATE - V

? i g . l . Showing climbing r ipp l e laminat ions from overbank deposi t s .

P ig ,2 . Showing small sca le r i p p l e s i n s i l t under massive mud,

19

Lenticular bedding may develop by current or wave

action depositing the sand alternating with stack water

conditions, when mud is deposited Reineck (1960a,b). The

sand lenses are made up of foreset laminae of current

ripple, when ripples migrate a muddy substance, the supply

of sand or silt is laminated, the isolated ripple trains as

lenticular bedding may be preserved Lindholm (1987).

Therefore it is interpreted that the lenticular

laminae were developed due to fluctuations in the current

velocity. Unsteady sediment transport associated with the

turbulent brushing process formed the lenticular laminae

Bridge and Best (1988).

Massive silt and mud facies (Fm): Massive silt and muddy

facies may have been deposited by suspended load after the

flood and may be interpreted as over bank flood sediment

plate V(Fig.2). This facies may also associated with minor

creavas splay deposits, mud layers gives idea about the

number of flood episodes occured during the deposition of

particular sedimentary unit. These facies occupies the top

portion of the bank deposits and generally lying above the

cross bedded sandy facies. The thickness of this facies goes

up to 4 m at some places.

Massive units are the result of rapid sediment supply

from high energy flows Fielding (1986). Massive units may be

interpreted as the result of sediment transportation in

20

planar sheets under very high energy conditions. Rust (1972)

and Lindholm (1987), described massive units formed by

sedimentary gravity floods which lack a mechanism to

produce primary structures. The structures are destroyed

due to upward movement of pore water by bioturbation mollted

nature of concentrations present in the sandy massive

units, indicate the product of post depositional phenoraenon

silt and clayey massive units are interpreted as having

formed by heavily laden water current during waning

periods of floods stage.

Similar interpretation of massive units having fine

sand and silt representing rapid deposition by suspension

fallout from possible flood flows Morison and Hein (1987).

21

CHAPTER III

CHAPTER III

DISTRIBUTION OF GRAIN SIZE IN RELATION TO SEDIMENTARY

STRUCTURE

General: Grain size distribution of sediments are

important tools to understand the process and products.

During last few decades the environment of deposition has

been described on the basis of grain size distribution (Folk

and Ward, 1957; Mason and Folk, 1958; and Friedman,

1961; 1979). The statistical parameters such as mean size,

standard deviation, skewness and kurtosis of fluvial

environment were developed and described to understand the

fluvial processes.Inman(1949) distinguished three

populations (traction, saltation and suspension) on the

basis of shape and size of sediments. Moss(1962;1963;1972)

using the shape and size of the grains distinguished

subpopulations in traction, saltation and suspenions. He

further opined that fine sediments transported in suspension

usually have an upper size limit of about 0.07 to 0.1 mm,

saltation have an upper size limit of about 0.25 to 0.17 mm

and traction have an upper size limit 0.5 to 0.25mm.

Ten trenches were dug in study area to study the

vertical and lateral variation in grain size distribution.

Samples were collected from Tatipaka, Razole, Sivakodu, Rama

22

Raju Lanka, Sakinetipalli, Rameswaram, Doddipatla,

Elamanchilli, Chinchinada and Narsapur (Fig.l). The data is

listed in Table I.

Cumulative frequency curves were plotted on log

probability paper following Visher (1965;1969). The grain

size distribution was grouped broadly into three types of

probability plots mainly on the basis of number of

subpopulations and their percentage and sorting. The mean

size sediment ranges from 2.6^ to 0.03 0. Out of 23 samples

11 samples show medium sand, 8 samples are coarse, 3 samples

are fine and 1 sample is very coarse Table II.

The mean size of overbank deposits ranges from 2.1 ^ to

1.9^ . Out of 3 samples, 2 samples are fine sand and 1

sample is medium sand.

Inclusive graphic standard deviation values of the

samples under study range from 1.4 0 to 0.4ffl . Out of 23

samples, 13 samples were moderately sorted, 5 samples

moderately well sorted, 4 samples poorly sorted and 1 sample

well sorted Table II and III. Out of 3 overbank samples, 2

samples were poorly sorted, 1 sample moderately well sorted.

Sorting of sediments depends upon competency and stability

of currents. If currents are relatively of constant

strength, sediment will be moderately sorted to well sorted,

but fluctuating current will give rise to poor sorting. In

this study, most of the samples are moderately sorted, which

23

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26

indicate currents of moderate competency and persistency.

The inclusive graphic skewness (Skj ) values of the

samples under study area ranges from -0.07 pf to + 0.2 d.

Kurtosis values of the studied samples range from 2 d

to 0 . 8 f .

Ripple cross laminated sandy fades (Sr)

R.G. Walker (1963) has recognised three distinct types

of ripple-drift cross laminations in upper carboniferous

formation in S.W. England.

Type I: It is characterized by strong erosion of laminae on

the stoss side of the ripples and absence of grading.

Type III : It is characterized by an absence of erosion on

the stoss sides. Concentration of mud in the ripple troughs

and an upward gradual decrease in grain size and ripple

amplitude.

Type II: It is an intermediate form with some characteristics

in common with type I and III. He suggested that type I is

formed in fluvial and shallow water environments at a time

of net deposition of sediment Type III formed by turbidity

currents. Type II suggests hydrodynamic conditions

intermediate between fluvial or shallow water traction and

turbidity currents.

Ripple cross laminated sandy facies was analysed for

grain size at Tatipaka trench. Where this facies is well

27

developed seven samples were analysed (Tablelll). The bulk

of each sample from Sr facies showing two to three

populations (saltation, suspension or traction, saltation,

suspension) at lA, 2A, 5A, 9B and lOA samples (Fig.2-11),

consist three populations and 3A and 4B, samples consist two

populations (Fig.12-15). Sediment size of inflection points

of three population samples at coarser end between traction

and saltation range from -1.25 gf to 0.0^ and for those at

finer end between saltation and suspension from 2.5 of to 5.0

0. The inflection points in two populations coarser ends is

-0.25 0 to -3.9 0 and finer end is 5.0 0 , the above data

suggests the sediment load of Sr facies has been transported

largely by saltation and contains about 60 to 99 percent

whereas traction load comprises about 10 to 38 percent and

suspenstion load 0.5 to 3.7 percent. On the basis of above

results, the bulk of the sediment of this facies was

deposited under low flow regime conditions (Mial, 1978).

Overall the sand of Sr facies have a mean size (Mz)

ranging from 0.53 0 to 2.43 0 with standard deviation (CTI)

0.76 0 to 1.110, suggesting that the sediment is moderately

well sorted to poorly sorted, Skewmess (Skj ) ranges from -

0.14 ^ to 0.28 0, coarse skewed to fine skewed and Kurtosis

(Kg) from 0.82 r to 1.550 platykurtic to very leptokurtic.

28

99 99

u < u

< <D O a a

z UJ u a.

> u z 111

o u cc (1.

Ill

>

3

- 2 .0 1.0 2.0 3.0 4.0

GRAIN SIZE IN PHI UNITS

5.0

Fig. 2. Log probability plots of grain uize distribution in Trench No. 1.

29

99.99

U) - I < o

CD < OD O

a

z I j j <J tr lU a >-u z u r> o u a u. u >

3 Z

-2.0 1.0 2.0 3.0 ^.0

GRAIN SIZE IN PHI UNITS

Fig. 3. Log probability plots of grain size distribution in Trench No. 2.

30

0 0

? 0.75

a 111 a

15"- -i i-L. • • '

I

J U_ 0.01 0.1 1.0 0 0.01 01 1.0 0 0.01 01 10 0 0.01 0.1 1.0 2 00

MEAN SIZE S.DEVIATION SKEWNESS KURTOSIS (Mz) ( 0 ^ 1 ) (SKI ) (KG)

Fig. 4. Ver t ica l va r i a t i on in facies in r e l a t i on to Mean s i z e , S. devia t ion , Skewness and Kurtosis in Trench 1.

a. u t-Ul

Z

a u o

001

10

2 0 001 01 1.0 2 000 01 0.1 10 2 00 15 OS 0.5 0

MEAN SIZE S.DEVIATION SKEWNESS (Mz) ( O - I ) (SKI)

001 0.1 10 200

KURTOSIS (KG)

Fig. 5. Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench 2.

31

99 99

u —I < o

ffi < CD O

a

z Ul o tr 111 a. >• o z UJ O UJ

z

-2.0 -1.0 00 1.0 2.0 3.0

GRAIN SIZE IN PHI UNITS

4.0

Fig. 6. Log probability plots of grain size distribution in Trench No. 5.

32

0 0 r rjrw

»/> (T u • -

u z 2 0251 X a. UJ

o

is"- -L. J 0010.1 1.0 2.000.01 0.1 1.0 2.00-1.5-0.5 0.5 0

MEAN SIZE (Mz)

S.DEVIATION ( O - I )

SKEWNESS (SKI )

I I I 001 0.1 1.0 2 00

KURTOSIS (KG)

Fig. 7. Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 5.

33

99.99

<

CD

< m o a a.

z hi u CE U l

a

bJ 3 a u cr

>

3

3

-1.0 0 0 1.0 2.0 3.0 4.0

GRAIN SIZE IN PHI UNITS

5.0

Fig. 8. Log probability plots of grain size distribution in Trench No. 9.

34

99 99

- J <

01 < CD o a. 0.

z

a. UJ 0. >-o z i i j O bJ oc b.

>

Z o

-2.0 -1.0 00 1.0 2.0 3.0 40 5.0

GRAIN SIZE IN PHI UNITS

Fig. 9. Log probability plots of grain size distribution in Trench No. 10.

35

ao

K III • -U

tei O

1-0

1.0

Fig . 10,

J J . L JL L JL 0.010.1 1.0 2 000010.1 1.0 2.00-1 S -OS O.S 0 0.010.1 10 2 0 0

MEAN SIZE (Mz)

S.DEVIATION (a-l)

SKEWNESS (SKI )

KURTOSIS (K6)

Ver t ica l va r i a t i on in facies in r e l a t i on to Mean s i z e , S. devia t ion , Skev/ness and Kurtosis in Trench No. 9.

aor

z 5 1.0 X 0. w o

2X) u. JL I.S 2.0 2.500.1 1.0 20 0 -1.S-0.S OS 0 0.1 10 2 0 0

MEAN SIZE ( M l )

S.OEVIATION (O-II

SKEWNESS (SKI)

KURTOSIS (KG)

Fig. 11. Vertical variation in facies in relation to Mean size, S. deviatii Kurtosis in Trench No. 10 Mean size, S. deviation, Skewness and

36

9999

<

0 < (D O a. a

z

UJ

a.

bi 3 O UJ

a.

>

3

00 1.0 20 3 0 4.0

GRAIN SIZE IN PHI UNITS

Fig. 12. Log probability plots of grain size distribution in Trench No. 3.

37

99.99

UJ

< o

CD

< CD O

a. a.

u cr UJ Q. >-<J

z Ul <s UJ cr

UJ

>

3

-2.0 -10 00 1.0 2.0 3 0 4.0

GRAIN SIZE IN PHI UNITS

Fig. 13. Log probability plots of grain size distribution in Trench No. 4.

38

001

111 z z X

a bi O

15'

F i g . 1 4 ,

JL 0 200-1.5-0.5 0.5 0

SKEWNCSS (SKI)

0.01 0.1 1.0 2.0 0

KURTOSIS (KG)

0.01 0.1 10 2.000.01 0.1

MEAN SIZE S.DEVIATION ( M I ) ( O - I )

Vertical variation in facies in relation to Mean size, S. deviation, Skev/ness and Kurtosis in Trench No. 3.

0.0 r

lit

u z

a u o

075

15«- _i_

* I I I

_ l _ l 0010.1 10 2.0000101 10 0

MEAN SIZE (Mz)

S. DEVIATION ( < r - n

0 01 01 1 0 0

SKEWNESS (SKI)

0.1 1-0 2 0 3.0 (

KURTOSIS (KG)

F i g . 1 5 . V e r t i c a l v a r i a t i o n i n f a c i e s i n r e l a t i o n t o Mean s i z e , S . d e v i a t i o n , Skewness and K u r t o s i s i n T r e n c h No. 4 .

39

Planar cross bedded sandy fades (Sp)

The planar cross bedded sandy fades (Sp) have been

observed in all the trenches. The similar fades have also

been reported by Frazier and Osanik (1961) from point bars

of Mississipi river, Harms et al.(1963) in Red river,

Lousiana, McKee(1938) in the flood plain deposits of the

Colorado river, Arizona, Coleman(1969) in the channel bar

sediment of the Brahmaputra river. The floods may have

formed the sandy layers as indicated by trough cross

lamination.

The probability plots of eight samples collected from

different trenchs of Sp fades exhibit two to three

populations (Fig.2-17). This fades is well developed in

trenches and exposed sections at Rama Raju Lanka.

The sediment size corresponding to inflection points at

coarser end between traction and saltation ranges from -1.25

0 to 0.7^ and for those at finer end between saltation and

suspension from 1.90 0 to 5.0 0 . The bulk of sediment load

consists of traction 16 to 64 percent, saltation 70-90

percent load. Suspension load occurs in subordinate type 10

to 16 percent.

Overall sand is medium size with mean size (Mz) ranging

from 0.03 0 to 1.90 0 and standard deviation (cj-I) ranges

from 0.45 0 to 1.010 poorly sorted to well sorted Skewness

values showing that the sediment is coarse skewed to fine

40

99.99

UJ - J < o

0

tL

t£ Ui a. >•

z UJ

o UJ (T U. UJ

>

3

99.9

99.6

-99

98

95

90

60

70

60

- 50

40

H30

20

10

2

1

0.5

0.2

0.1

005

JL -L _L J_ •2.0 -1.0 0.0 10 2 0 30 4 0 5 0

GRAIN SIZE IN PHI UNITS

00

Fig. 16. Log probability plots of grain size distribution in Trench No. 6.

41

OOr

(T U t-Ui

z 5 10 z a bJ

o

zo"- " * - I - - i -1.0 2 0 3.0 0 0.1 10 2.0 0 1.5 0.5 0.5 0 10 2.0 3.0 4 0 0

MEAN SIZE (Hz)

S.DEVIATION ( O - I )

SKEWNESS (SKI)

KURTOSIS (KG)

Fig. 17. Ver t ica l va r i a t ion in facies in r e l a t ion to Mean s i z e , S. dev ia t ion , Skewness and Kurtosis in Trench No. 6.

42

skewed and range from SKj -.06 d to 0.23 gf, and kurtosis

ranges from (KQ) 0.1 0 to 2.02 d mesokurtic to very

leptokurtic.

This facies at Rama Raju Lanka the sand deposit is

medium sand with mean size (Mz) 1.31^. Moderately sorted(Q-

I) 1.01 (, near symmetrical SKj 0.06j^, and very leptokurtic

KG 2.013^ .

The average of eight samples of planar cross bedded

facies shows that the sand facies comprises of medium sand

(MZj) 1.06 (, it is moderately well sorted ((j-I) 0.90 j^,

fine skewed (SKj^)O.ll^ and leptokurtic (KQ) 1.11 d.

Trough cross bedded sandy facies (St) :

Trough cross bedded sandy facies occurring in the study

area results from infilling of trough shaped scours by

migrating dunes (Fig.12-17,19,21,22) The type of dune and

it's association with scours are still controversial. Allen,

(1963, 1965); Harms and Fahnestock, (1964). A better

understanding of large scale cross bedding in a

unidirectional current regime Jopling (1963). Harms et. al.

(1963) stated that the mechanism of scouring and infilling

of the scour pockets developed a tangential type of cross

stratification in relatively high velocity and a high depth

ratio.

43

The cumulative probability plots of sand facies with

large scale trough cross bedding for grain size analysis of

five samples in the study area collected, at Tatipaka,

Sivakodu and Razole, show intersecting plots with one or two

inflection points. The first inflection point between

traction and saltation range from -1.25 Of to 2.5 Jf and

second point from saltation and suspension lies between

1.3 ( to 5.00^ . The bulk sediment load consists of traction

10 to 77 percent, saltation 35 to 65 percent and suspension

load occurs subordinate type 5 percent.

This facies consists mostly of coarse sand with mean

size (Mz) varying from 0.23 Cf to 1.23j^ ; moderately sorted

Ca~I) 0.710 to 1.23^. It is near symmetrical (SKj ) 0.006^

to 0.028 0) and commonly mesokurtic (KG) 0.78 of to 1.41^.

At Tatipaka, Sivakodu and Razole the large scale trough

cross bedded sand facies is coarse grained (Mz) 0.822^

moderately sorted {0~ 1) 0.31 C . It is fine skewed (Sj j )

0.035 (/i and mesokurtic (KQ) 1.00 0.

Horizontal bedded sandy facies (Sh)

Horizontal laminations in turbidites may be related to

migration of long wave length antidunes, Middleton and

Hampton (1973), Moss (1972). Horizontal bedding can develop

at all motion intensities from the small ripple stage. The

mega ripple stage, while due to flow unsteadiness,

44

bedforms sometimes fail to develop. The horizontal bedded

sandy facies (Fig.26-27) graphic plots of cumulative weight

percentage yield two sediment populations, saltation and

suspension. The saltation populations constitutes 98

percent, supension 1.3 percent. The sediment size at

inflection point at coarser end, between saltation and

suspension 0.5 0 to 3.5 fij and for those at finer end, 3.5^

to 5.0 .

The facies is fine grained with mean size (Mz) 2.0 ^

moderately well sorted (cj-I) 0.69 (, symmetrically skewed

(Sj j ) 0.02 ( and mesokurtic (KQ) 1.05 (J.

Lenticular sandy facies (SI)

This facies is well developed at Rameswaram,

statistical parameters of this facies showing two

populations saltation and suspension(Fig.28, 29) . The

sediment size corresponding to inflection points at coarser

end between 0.5 0 to 4.25 0 and for those at finer end

between 4.25 ( to 5.00 0 . The sediment load consist of

saltation 98 percent and suspension 1.3 percent.

Sand size is fine grained with mean size (Mz) 2.67 (,

standard deviation (Q- I) 0.69 ]? moderately well sorted;

near symmetrically skewed (Sj j ) 0.01 ( and kurtosis (KQ)

3.42 ( is leptokurtic.

45

Parallel laminated fine sandy facies (Fl)

Veiry small scale ripple fine sand facies was analysed

for grain size at Elamanchilli trench (base of overbank

deposits). One sample was analysed (Table III) and data were

plotted on log probability paper as shown in (Fig.18,19).

The sample from Fl facies consist of two populations

(saltation and suspension).

Sediment size corresponding to infelection points at

coarser end between saltation and suspension ranges from 1.0

J3 to 4.1 of and for those at finer end, ranges from 4.1^ to

5.0 . It constitutes 98 percent saltation load and 1.0

percent suspension load. It may be inferred that sediment

load of Fl facies has been transported largely by saltation

load.

The mean size of Fl facies is (Mz) 2.7 p fine sand,

with standard deviation ^ I ) 0.68^ moderately well sorted,

skewness (Sj j ) 0.090 (J fine skewed; and kurtosis (KQ)

0.778 ^ platykurtic.

Massive silt and clay facies (Fm)

This facies is well developed in overbank deposits of

Godavari river. Probability plots of two samples exhibit two

populations saltation and suspension. Sediment size of

inflection points at coarser end of saltation and

suspension 0.5 m to 3.5 0, and those at finer between 3.5

46

99.99

< o

< OD O

a a.

o a III a. y-

3 O Ui

a

z O

• ^ -

-2.0 -10 1.0 2.0 3.0 * 0

GRAIN SIZE IN PHI UNITS

99.9

996

99

98

9S

90

80

70

60

SO

40

30

20

10

2

1

0.5

0.2

0.1

OOS

Joo

;

F i g . 1 8 . Log p r o b a b i l i t y p l o t s of g r a i n s i z e d i s t r i b u t i o n i n Trench No. 8 .

47

00 r

(A a. ill » -Ui z

a. tii o

20

4.0' 0.010.1 10 2.000.010.1 10 2.000.010.1 1 0 ^

MEAN SIZE S.DEVIATION SKE\WNESS (Mz) ( o - I ) (SKI )

t M • I

0.01 0.1 1.0 0

KURTOSIS (KG)

Fig. 19. Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 8.

48

0 to 5.0 0 (Fig.20;21). These samples constitutes saltation

load 64 to 71 percent and suspension load 27 to 37 percent.

This facies is consists of fine sand with mean size (Mz)

1.96 0 to 2.67 0, poorly sorted (orl) 1.005 to 1.447 0". It

is coarse skewed to fine skewed (Sj j ) 0.176 ^ to 0.288 0

and mesokurtic to leptokurtic (Kg) 0.91 0 to 1.19 d.

Vertical variation in grain size :

As per cumulative plots, the verticle variation in

grain size shown at various down stream localities along the

distributary channels of Godavari. The mean sand size is

increasing upward from 0.53 0 to 2.49 0 at the base, 0.033 0

to 2.67 0 middle part and 0.233 0 to 2.0 0' at the top. All

trenches show two cycles of sediments occurring in the 1.5

to 2.0 meter thick seguence. The grain size parameters

exibits a slight vertical variation in most trenches.

However, there is a tendency of increasing mean size from

base to surface.

The grain size characters show distinct change in

sorting. The lower part of the sequence is poorly sorted and

the middle part is well sorted, whereas the upper part

again show poor sorting.

49

99.99

u <

ffi

< CD O CC

a.

IE

a.

UJ 3 a u b.

UJ >

3 Z

•2.0 -1.0 0.0 1.0 2.0 3 0 4.0

GRAIN SIZE IN PHI UNITS

Fig. 20. Log probaility plots of grain size distribution m Trench No. 7.

50

0.0

Ui

UJ

Z z

a bJ o

1.5

3.0>-

SKl -0 17

KG 0.91

Fig. 21. Vertical variation in facies in relation to Mean size, S. deviation, Skevmess and Kurtosis in Trench No. 7.

51

CHAPTER IV

CHAPTER IV

MINERAL COMPOSITION OF 60DAVARI SEDIMENTS.

Twenty samples spreading all over the area under

investigation were examined for determining the mineral

composition and other petrographic characters. The

volumetric proportions of the sediments is listed in Table

IV The following minerals were recognised from the samples

collected from various localities; quartz, opaques, garnet,

amphiboles, pyroxenes, sillimanite, kyanite, staurolite,

sphene, epidote and zircon (Fig.22-29).

Quartz : Quartz is most prominent mineral and on an average

20.54 percent in Godavari river sediments. Generally grains

are angular to subangular but some in grains rounded out

lines are common. The angular grains show fractures, while

subrounded grains are marked with smooth surfaces. The

grains show straight/wavy extinction.

Opaques: Opaques are most abundant of all the minerals and

comprised on an average 27.58 percent of the sediments.

Generally, opaques are subrounded to subspherical. In plane

polarized light most of the grains are dark coloured.

Garnet: Majority of garnet grains are subrounded to sub

spherical. Two varieties of garnets were recognised,

almondite type showing pink or purple red colour and

52

TABLE:- IV MINERAL COMPOSITION OF GODAVARI SEDIMENTS.

SAMP. /WHiaOLES

No. ACTINXI7E/

aJART7 OP/XaJES GAWET HOfi taf lO HYPER- DIOP- SILLIM- IOTA- STAURO- SPHBC EPI- ZIR- TOTACC

tme SIDE ANITE NITE Q T E DOTE CON

1 28.10 24.« M.fB 22.28 1.80 1.24 4.65 0.50 - - 0.75 0.30 97.76

2 21.55 21.51 18.26 20.12 0.95 0.46 3.71 1.0 0.65 0.25 1.50 0.25 90.21

3 27.61 18.75 20.40 16.Z3 1.87 1.06 5.0S 0.33 0.50 0.33 1.06 0.45 93.64

4 20.0B 26.07 16.76 21.03 1.06 1.10 4.03 1.15 0.58 0.35 1.36 - 92.52

5 18.13 24.73 5.64 22.36 0.48 1.03 6.47 0.11 0.69 0.24 1.49 - 81.35

6 13.30 42.76 16.81 9.95 1.25 1.16 2.03 0.27 0.79 0.26 0.95 1.40 90.91

9 15.95 33.Z3 12.05 20.80 0.85 0.75 4.60 0.31 0.56 0.09 1.85 2.00 92.92

10 19.64 29.20 16.30 18.65 2.37 0.70 6.00 - 0.25 - 1.13 0.12 94.36

Avg. 20.54 27.58 14.98 18.92 1.32 0.93 4.56 0.52 0.57 0.25 1.26 0.75

53

grossutorite showing light brown colour. It constitutes on

an average 14.98 percent in composition (Fig-30).

Amphiboles:

(a) Actinolite: Grains are fresh and unaltered. The colour

of these grains showing green to greenish blue. The

grains are subangular to subrounded in shape.

{h) Hornblende: The hornblend grains are greenish brovn to

light brown in colour and are elongated. Hornblend

grains displaying pleochroism in shades of dark

brownish red are rarely observed. The average

percentage of amphiboles is 18.92 in Godavari river

sediments (Fig.30).

Pyroxenes:

(a) Hyperthene: Generally hyperthene is prismatic in shape.

It commonly displays light green to purple pleochroic

scheme and green to greenish yellow. It constitutes on

an average 1.32 percent in the sediments (Fig 30).

(b) Diopside: Diopside grains are subrounded to well

rounded. Colour of these grains are in shades of light

grass green in pleochroic scheme. It constitutes on an

average 0.93 percent (Fig.30).

Sillimanite: One set of prismatic cleavage is very common

in sillimanite grains. Large grains showing inclusions of

54

quartz and opaques. Most of the grains are subrounded. The

average percent of sillimanite in Godavari river sediments

is 4.56 (Fig.30).

Kyanite: In kyanite, grains show two sets of prismatic

cleavage. They are generally colourless and rarely showing

light blue colour. A few rounded grains are observed. It

constitutes on an average 0.52 percent (Fig.30).

Staurolite: Staurolite grains are prismatic. The grains

display two types of pleochroic schemes. One deep rust brown

to honey brown, and the other orange to yellow. Most of the

grains show straight extinction. Inclusions are rarely

observed. The average composition of staurolite in Godavari

river sediments is 0.57 percent (Fig.30).

Sphene: These grains occur either as irregular or sub

rounded, grains showns brown in pleochroic scheme. Number of

irregular cracks are commonly observed and on an average

constitutes 0.25 percent (Fig.30).

Epidote: Epidote commonly occurs as subrounded to irregular

grains in shape. Most of the grains display distinct

pleochroism either bright green grass to greenish yellow,

few grains showing shades of olivine green in pleochroic

scheme. It constitutes on an average 1.26 percent in

Godavari river sediments (Fig.30).

55

zircon: Most of the zircon grains are either euhedrai or

subhedral in shape. These grains are not showing any

growths, few of the grains have corroded prismatic faces,

perfect crystals which either prismatic or prismatic

pyramidal are common, indicating euhedrai grains show

variation in colours and are rounded. Zoning is common in

these grains are free from inclusion and constitutes on an

average 0.75 percent in Godavari river delta sediments

(Fig.30).

56

Fig. 22. The mineral composition of Godavari sediments (in percent) in Trench No. 1. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphibol-es; (5) Hyperthene; (6) Diopside; (7) Sillim-anite; (8) Kyanite; (9) Epidote; (10) Zircon.

Fig. 23. The mineral composition of Godavari sediments (in percent) in Trench No. 2. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphibo-les; (5) Hyperthene; (6) Diopside; (7) Silli-manite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon.

.c-

0.30(10)

mil

F i g . 22

0.25(12)

F i g . 23

57

Fig. 24. The mineral composition of Godavari sediments (in percent) in Trench No. 3. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon.

Fig. 25. The mineral composition of Godavari sediments (in percent) in Trench No. 4. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote.

0.3302) .33(11)

F i g . 24

K >

0.35(11) 0.58(10)

^< P

F i g . 25

58

Fig. 26. The mineral composition of Godavari sediments (in percent) in Trench No. 5. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote.

Fig. 27. The mineral composition of Godavari sediments (in percent) in Trench No. 6. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon.

o €-

0.11(11)

F i g . 26

o

F i y . 27

59

Fig. 28. The mineral composition of Godavari sediments (in percent) in Trench No. 9. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon.

Fig. 29. The mineral composition of Godavari sediments (in percent) in Trench No. 10. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Staurolite; (9) Epidote; (10) Zircon.

|0.09(12) 0.31(11) '0,560o;

% s/

F i g . 28

F i g . 29

60

Fig. 30. Average mineral composition of Godavari sediments (in percent). The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon.

0.25(12) 0.5?()i)

F i g . 30

61

CHAPTER V

CHAPTER V

FLOW PATTERNS

Sorby (1859) was the first to systematically measure

the cross-stratification, but did not publish.Brinkman

(1933) was the first to give a clear concept of paleocurrent

study. Potter and Olson (1954) used the cross-stratification

as a tool for determining the paleocurrent. Recent studies

of the dispersal patterns and basin analysis with the help

of primary sedimentary structures of modern environments,

were taken by Williams (1971), Picard and High (1973), Smith

(1970), Coleman (1969) and Killing (1969). The present study

aims at recognition in variation in flow patterns with the

help of primary sedimentary structures (cross

stratification). Suitable trenches were selected in the down

current direction and orientation of the cross-bed foreset

planes were recorded. Two types of cross-stratifications

namely plain and trough are occurring in the study area. In

case of planar cross-stratification, dip azimuths were

directly measured with the help of clinometer compass,

whereas for the trough cross-stratification, azimuth of the

acute bisecrix of the curved surface was taken as a true

azimuth of the foreset surface. A total of 415 measurements

of the cross- stratification azimuths spread over 8

localities were made.

62

The rose diagrams (Fig31) show distribution of dip

azimuth at locality level and sector level. The arrow

indicating vector mean ( v) and vector magnitude (L%).

Vector mean ( v), were calculated by following vector

simmition method of Curry (1956). The results are shown in

Table No. V.

VECTOR MEAN

Vector mean ( v) is the most commonly used and accepted

parameter dealing with the orientation data (Curry 1956;

Potter and PettiJohn, 1963). Curry (1956) stated that the

vector mean provides a unique value of central tendency,

irrespective of choice of origin of measurements.

The vector mean values determined for 4 localities

ranges from 106 to 197 and at sector level is 165 . At

sector B, the vector mean was determined for 4 localities and

C O * the values ranges from 75 to 230 and at sector level xs

0 180 .

VECTOR STRENGTH

This parameter is necessary to determine the magnitude

of the resultant of cos and sin components. Curry (1956) and

many others indicate that 'L' is the vector strength or

consistency ratio, provides some indication of dispersion.

The vector strength (L%) was calculated at locality level

and at sector level. At sector A, the vector strength ranges

63

Fig. 31. Map showing variations in flow direction from general flow direction. Rose diagram showing frequency distribution of cross stratification azimuths in 30° class interval in percent, Numbers within Circle represents Trench Number. Arrow indicates vector mean.

64

TABLE NO. V COMPUTATION OF VECTOR MEAN AND VECTOR MAGNITUDE

OP CROSS-BEDDING AZIMUTH

SECTOR UXAQTY UDCAU7Y LEVa SECTOR LEVEL

NUfBER

n V L I S ^ n V L I S ^

(in degree) (in percent) (in degree) (in percent)

57 106 89.83 28.73 825

A

B

2

3

«

5

6

9

53

58

67

39

41

46

190

197

127

162

Z30

75

87.55

92.00

82.81

84.98

90.24

82.00

31.00

35.15

34.75

32.86

28.38

35.00

963

1255

1206

1080

806

1880

235

180

165

140

78.02 21 461

53.0B 68 4630

10 54 ICS 87.00 32.00 1053

n = Number of o b s e r v a t i o n s

V = Vector mean

L% = Vector magnitude

1 = Standard d e v i a t i o n

2 S = Variance of c r o s s - s t r a t i f i c a t i o n d ip azimuths.

65

from 82.81 to 92 percent at locality level and is 78.02

percent at sector level. At sector B, the vector strength

values ranges from 82 to 90 percent at locality level and

53.03 percent at sector level.

VARIANCE

The degree of scattering around the mean is measured

quantitatively in order to define the population of vector

azimuth. The variance (S) of foreset dip azimuth at the

sector level varies from 461 to 4630 in the area under

investigation. These values are the indication of the

scattering of dip azimuth about the mean and are numerically

equal to the square of standard deviation. The variance

significantly shows large variance in the current direction.

The variance values of cross stratification azimuths of

Godavari delta sediment A 481, B 4636. Sector A is minimum

value of 4000-6000 generally attributed to fluvial sequences

(Potter and PettiJohn 1963), and Sector B value fall within

the range and the inflated sector variance may be

integration of the various flow-systems represented by

regional components. This variation is due to variability in

attitude of superimposed bed-forms within the channel fill

of Godavari sediment.

66

INTERPERTATION

Synthesis of the data reveals that the current

direction obtained from the orientation data, by and large

coincides with the present flow direction of the river. But

it is not applicable for all over the area under

investigation. However, Godavari river shows large variation

in flow pattern from those indicated by the orientation

data. The nature of the river system prevailing at the time

of the deposition of that particular cross-stratified unit.

The Godavari river being of the distributary channels

of nature, did not flow constantly in the same direction for

a long distance due to the presence of bars, developed in

the earlier cycle of the deposition. The sediments deposited

on the bank during floods show large variation in the

current direction from the main flow.

67

CHAPTER VI

CHAPTER VI

DELTA MODEL

The detailed study of the sedimentary structures and

facies architecture of Godavari river delta showing various

types of flow regimes. A depositional environment is a

complex of physical, biological, chemical, tectonic and

climatic conditions, prevailing at the time of deposition

Shepard and Moore (1955). The first three of these

attributes are of local character and determine the

environment of depositional site. While tectonic setting and

climatic conditions are broader controls which impress

certain common character on sediments deposited in the basin

under different local conditions and tie them into a

consangeinous association. Seasonal variations control the

deposition, so that at the time of high discharge the river

transports more gravels than sand. The coarse clasts at the

base represent deposition by lateral accriation. On other

hand fine sediments represent vertical accriation on top of

channel bars (Smith 1974, Cant 1978). During low discharge

smaller thickness of fine clasts sediments suggest

preservation and rapid shifting channel bars. In the present

study, an attempt has been made to develop a depositional

model for the river Godavari. Eight trenches were made on

the river channels and two from overbank deposits. The

trenches dug in the channels are characterized by coarsening

68

upward sequence (Fig.32). The block diagram shows

generalised sequence from river channels to overbank

deposits (Fig.33).

The bottom of the trench shows parallel laminations of

current ripples. The current ripples represent a supply of

coarse sand in large amount and parallel laminations

indicate fine grains and zero current velocity. Current

ripples underlain by trough cross bedding, these large scale

trough cross bedding are supposed to form in the upper part

of low flow regime (Simon and Richardson, 1961). The

formation of crossbedding is controlled by current velocity

and flow characteristics and rate of sediment supply and

infilling of scours by migrating dunes.

Trough cross stratification, overlain by planar cross

stratification (Fig.32), the sediments were migrated in the

bar surface and slip on the avalanche face resulting in

planar cross stratification Morison and Hein (1987). The

planar cross stratification perhaps forms due to migration

of bars. In turn the planar cross stratification overlain by

pebbles bed in coarse sand laminations suggesting unstable

high seasonal floods Morison and Hein (1987).

Overbank deposits showing upward fining sequence, with

small scale ripples overlain by climbing ripple

laminations. Small scale ripples and climbing ripple

laminations may have developed by current or wave action,

69

L

MASSIVE MUD

CLIMBING RIPPLE LAMINATION

SMALL RIPPLE BEDDING

PARALLEL LAMtNATIONS

PLANAR CROSS BEDDING

TROUGH CROSS BEDDING

CURRENT RIPPLES

PARALLEL LAMINATIONS

OLDER SEDIMENTS

FI6.( 32) GENERALIZED SEQUENCE OF 60DAVARI RIVER DELTA .

70

Fie,'. 33. Block diagram showing Bedforms stratifications of the Godavari Delta.

ind

71

depositing sand, silt and clay with stack water. These

climbing ripple laminations overlain by muddy massive unit,

which indicate the slow moving conditions.

The sedimentary structures and sediment size differ in

the sequence developed in the channel and the overbank.

Generally the channel deposits show coarsening upward cycle,

where as the sequence developed an the overbank has fining

upward sequence.

72

CHAPTER VII

CHAPTER VII

CONCLUSION

The river Godavari is the greatest river of South India

running from Triambak to Bay of Bengal (900 miles). It

deposits vast quantity of sediments, resulting in formation

of Godavari delta. Under the area of investigation, the

river shows straight flow pattern carrying sediments of

various size.

Seven sedimentary facies have been recognised namely,

trough cross bedded facies (St), planar cross bedded facies

(Sp), ripple cross lamination facies (Sr), horizontal bedded

facies (Sh), parallel lamination bedded facies (Fl),

lenticular bedded facies (SI), and massive mud silt and clay

facies (Fm).

The cross-stratifications both planar and trough are

most abundant facies. They are produced by the migration of

sand ripples in the down stream with lateral growth of

channel bars. The ripple drift cross laminations second in

abundance and occur in two forms. One in which laminae are

in phase and other in which laminae are in drift. Low

current velocity and abundant supply of sediment is

responsible for the formation of this facies. Whereas, the

horizontal laminated facies developed in sands deposited in

a upper flow regime. Apart from these facies, there are

73

other distorted facies i.e., parallel laminated facies

developed in zero current velocity. Climbing ripples are

post depositional and produced due to unequal loading.

Massive muddy facies covers the large part of the deposits

is regarded as post depositional structure. Lenticular sandy

facies is another type of facies produced due to short lived

current carrying sands.

Towards the down stream of the distributary channels

the mean size of sand decreases whereas sorting slightly

increases, skewness changes from negative to positive, while

kurtosis remains almost unchanged.

On the basis of mineral composition, it is concluded

that the provenance of the Godavari river sands consist

chiefly of the precambrian khondalites, charnokites, and

calc-granulites, and to a smaller extent of the Dharwars and

the Gondwanas. The Deccan traps consist more than half of

the drainage basin of the Godavari river, but there is no

specific heavy mineral species present in the sands of

Godavari river sediments studied, which points out to the

Deccan trap provenance. All the samples of Godavari river

sands the total heavy mineral content by weight is

relatively high in the results presented in the foregoing

paragraphs.

The distribution of the dip azimuths of cross

stratifications show variations in current direction from

74

general flow pattern due to development of a distributary

channels. It is quite clear that there is a lateral and

vertical variation in the sedimentary facies, texture and

mineral composition of the deltaic sediments of the Godavari

river investigated. It is summarised that these variations

may be used to decipher the down stream direction of the

paleoestuarine channel and also the various environments of

deposition of a paleodelta which had a geological setting

similar to that of the modern Godavari delta.

75

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