Lithofacies and Sedimentary Structures of Yamuna River Around Brindaban

Dist. Mathura

DISSERTATION SUBMITTED IN PARTIAL F U L F l t M E M T OF TME

REQUIREMENTS FOR THE AWARD OF THE DEGREE O F

Mnittx of ^Ijilosiopljp IN

Geology

BY

SYED DANISH RAZA M. Sc .(Alig.)

DEPARTMENT OF GEOLOGY ALIGARH MUSLIM QNIVERSITY

ALIGARH (INDIA) SEPT. 1986

o i l / - vv/ -' ^^ -"• '••*

DS926

,D. Bhardvvaj M . S c , Ph.D.(AMU) S u p e r v i s o r

Telepl'.onc No. : 5615

DEPARTMENT OF GEOLOGY ALIGARH MUSLIM UNIVERSITV

AUGARH-202001

Date.Sep.tember 4^1986

I certify that the work presented

in this dissertation has been carried out

by Mr. Syed Danish Raza, M.Sc.(AMU),under

my guidance. The work is an original one

and has not been submitted for any other

degree at this or any other University.

( B.D. BharcSwaj )

C O N T E N T S

Chapter-I

aiapt9r~XI

Chapter-XIX

INTHOSUCTION

Yamuna Hiver

Gaoiaorphic features

Study area

SaapXing and AnaXyticaX Techniques

^kncKvXedgement

ULIHOFACIBS

Overbank Deposits

Point bar deposits

SmW^ntMiY STHUCTIBES AM) fLiM PATTERNS

aippXe Drift Cross Lmination

Cross Bedding

ConvoXute Bedding

HorisontaX Bedding

wavy Lamination

Massive Units

FXow patterns

Vector ii^an

Vector strength

Variance

• • •

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Page

X

3

4

5

5

8

9

9

X2

X6

X6

2 i

26

^

32

33

34

35

35

36

Chapter->IV GRAXH SIZE ANALYSIS • • • 37

- l i -

Chapt03C-V tUHERAL Ca^POSlTlON • • • ^^

Chap t e r -V l FLUVIAL / CDEL • • • A^

kode l - A • • • ^^

M©d«l - S • • • 46

O i a p t e r - V I I CoriCLUSION • . . 48

Hefe rances • • • SO

L I S T OF F I G U R E S

Facing page

Figure - X i ap of the stuciy area • ••

Figure - 2 Showing iithofaeies distribution

Figure - 3

Figure - 4

Distribution of sedimentary structures in bank deposits

Distribution of sediii^ntary ••• structures in point bar deposits

16

16

Figure - 5 Map showing variation in current direction froia general flow patterns 34

Figure - 6 Histograms shmving mechanical ABCD em£|>osition of Yamuna sands ••• 38

Figure - 7 Cumulative curves for Yamuna sands • •• 38

Figure - 8 Representative trenches of bank deposits • •• 44

Figure - 9 Representative trenches of bar deposits • • •

Figure - 10 f4odel - A

44

44

Figure - 11 Model - B 44

L I S T OF P L A T E S

Facing l>ag«

Plate - I F ig . 1-2

Field photf^raphs showing ripple d r i f t crest lai&ination • • • 16

Plat© - 2 Fig0^2

Field photographs shewing cross bedding • •• 21

Plate - 3 Fig. 1-2

Field photographs showing convolute bedding • • • 26

Plate - 4 Fig* 1

Fig . 2

Field phot«^raphs showing horizontal bedding

Field photographs shmving oassive unit

• • •

• • •

30

30

Plate - 5 Photographs (fi Ulcro) of various ^^d.nerals of Ysaauna sand «•• 4C

L I S T OF T A B L E S

Table - 1

Table

Table

Table

2

3

4

Vector mean* Vector magnitude standard deviation and variance of cross bedding dip azimuths »•«

Grain size frequency distri­bution (Percent) of Yamuna sands••

Statistical parameters of size frequency distribution •*•

Mineral coi^osition of Yamuna sands •••

34

37

37

39

N

M^THURA CITY

S o I I KM

h Fig.l Map Of The Study Area .

C H A P T E R - I

INTHODUCTION

The Study of 8«dloi«ntaxy processes and products in

a knovm environment is helpful in reconstructing the

ancient sedimentary deposltional environments. The deposi-

tional processes leave their imprints in the sediments

deposited during geologic past. Passega (1962) established

that the study of recent sediments searve& as the mediocre

mean in understanding the ancient sedimentation* Friedman

(1961» 1967, 1979) on the other hand strongly supported

the significance of study of recent sedimentation in

interpreting the ancient sedimentary environment if Boam

limitations are kept in consideration. Visher (1969) while

admitting that ancient sediments show some minor deviation

from their modern analogous. However» Gees (1965), Kleven

(1966) and Sevon (1966) told that the study of modern

sediments is not of great importance because of so many post

deposltional changes.

Sedimentary enviroiment can be defined in terms of

physical, chemical and geomorphic variables. The study of

the physical processes is most important and provides the

basic information for geomorphic interpretation. The factors

such as changes introduced during diagenetic, epigenetic,

chemical and biological transformation, mixing of environ-

-2-

latoral and v«rtieal fades variation* timo and othar

factors must also bo takon into con*iteration* Notwith­

standing » tiM abovo sionti<m0d views th« studios of tho

recent sediments provide the iMist tool for the reconstruct-

tion of the ancient envir(»»M»nt of deposition* •

Meandering and Braided are the two laain typss of

river sys^ua noted in the geological literature* Many studies

have been made in the recent years on oodern rivers* Allen

(1965» l97o)t Miali (i976» 1977>, Shelton «nd Noble (1974}>

Friectean (1979)* JfUist (1978) in order to determine how the

sedimentary structures and other bedding characters are

formed* In the present study an attempt has been made to

determine th« nature of sediments depcMiited by the action

of lateral accretion on point bars and the vertical deposits

on flood plains due to overbank flooding of the yamuna river*

To achieve these objects the different faeiee a nd their

internal struc^res in relaticm to differwit bed-forms have

been recognised to reconstruct the appropriate fluvial

GT'Odei for Yamuna river under the following heads*

1* The flood plains and river channel facies on the exposed

surface along trenches and in cuts on the banks*

2* Various sedimentary structures» their geometry* lateral

and vertical association and orientation were examined

and a local flow pattern was worked out*

.»

3. ni« s«diiB«nts w«r« anaXystd for grain size and mlnara-

logical charactars. On tha baaia of tha abova studiaa it

haa baan posaible to raconstruct two aaparata fluvial

modala each for bank daposita a nd point bar daposita of

Yamuna rivar«

YAMlAiA RIVER

Tha Yaonina rivar is one of tha most important rivar

of Gangas rivar syatem of North India anc oceupiaa wastarn

most position in this systam* As tha sourca of Yamuna

river is concemad, tha Yamuna rivar originata? from tha

Yamnotri glaciar at an alavation of 6320 m abova maan aaa

laval naar B«idurpunch in tha ly^saooria rangaa of lowar

Himalayaa of Uttar Kashi (U«P«)« During ita coursa from

Uttarkashi to Allahabad a larga numbar of smaller straama

join tha main rivar at various loealitiaa» Of tha wastarn

atraam tha Riahi Qanga joina tha Yanuna rivar at ita right

bank naar Banas» a^ila tha two othar straan^ tha Utna and

Kanuman Ganga mat tha main rivar on its laft bank* Thara

ara alao savaral atraama originating frcm tha lowar

Himalayan rangas and ridgas join tha Yamuna rivar* Aftar

joining tha Toria rivar» which is tha main sourca of watar

in tha mountainaoua r4Bigaa» tha Yamuna rivar antars tha

Musaooria hilla and than braaks tha hills to ba joinad by

Qiri and Ahaan rivara* Aftar flowing up to a diatanca of

u

200 km the Yamuna river emerges from SiwaXik ranges into

plains near Saharanpur in Uttar Pradesh, vthiere it flows

in a broad curve through Delhi* Mathura» Agra and then

Joins Ganga at Allahabad city having an elevation of 100 m

above niean seal level. During its course from Uttar Kashi

to Allahabad it covers a distance of 1 3 ^ km and exhibits

various patterns i.e* steep drainingy braided and

meandering*

GEOMQKPHIC FEATURES

In the study area the following geoo»rphic features were

observed:

(a) Lateral Accretion Deposits:- These deposits

include the point baxs and margin bars vmich have been

formed as a result of the lateral migration of the channel*

These deposits mostly consist of sand and occupy the marginal

boundaries of an active channel*

(b) Vertical Accretion Depositsi- These deposits

include natural levee and back* swamp deposits a nd have

been developed as a result of the suspended load of the

available flood water. These deposits are characterised by

fine grained sediiMnts anali occupy the overbank flood plains*

..»

(e) Splayst> Splays axe also included in

ovezbank flood plains deposits* These deposits are formed

as the bed load materials accumulate locally and spread

from channels onto adjacent flood plains*

STUDY AREA

The present area of investigation lies in Mathura

district of Uttar Pradesh between 77®40 to 77°43' east

longitude and 27**30* to 27**45* north latitude falling

within the Survey of India toposheet no.54 E/lO covering

159 sq« km between Magla Garhi village (situated in the

northeast at a distance of one kilometer) to Mathura city

(Fig. 1) showing the meandering patterns*

SAMPLING AND /U4ALYIXCAL TECHNIQUES

The method employed in the present investigation

to study the various characters of Yamuna sand was to dig

trenches with the help of a showel and Khurpa at different

localities* A total of 25 trenches were dug* The trenches w«

were made to expose the primary ^sedimentary structures*

The width of the trenches ranges between 1*25 to 4 m and

length from 3 to 4 m* However, this depth width ratio was

either decreased or increased depending upon ^ e height of

the river deposits* Most of the trenches wese dug parallel

(}

to th« direction of flovv of river but three dimensional

trenches were also dug wherever needed* The trenches were

made si&ooUi with the help of a chopper and were left

exposed to air and sunlight to dry them* The process of

making them dry proved helpful in observing the stratifi­

cation and other sedimentary structures* Samples from both

the banks of river as well as from the point bar deposits

were collected to determine the e^chanical and mineralogi-

cal characters of the sediments* The whole area was

divided into six sectors* Each sector was comprised of at

least 2 to 3 localities a nd stratigraphical section were

measured at each locality* The study of the sedimentary

structures present was made in the light of their shape»

orientation* size asn6 li^ology constituting them* * The

vertical and lateral relationship of the structures was

determined* Further* to study their characteristics, photo­

graphs and sketches were also aade* Ttie azimuth of the

planer cross stratificati(m were measured with the help of

a clinometer compass* in ease of trough cross stratifica­

tion the azimuth of the acute bisectrix of the curved

surface was taken a s the true azimuth and the data

collected were grouped into 30^ classes* The vector mean

(GV)t vector magnitude (£ .) and standard deviation for each

sector and locality were calculated using vector sumndtion

method (Curry* 1956}* The rose diagrams were also plotted

with the help of dip azimuth of cross stratification

forset to show the direction and modality of the current.

For the grain size analysis the samples were collected

from both bank as well as from bar deposits at a regular

interval of 50 m. At some places distance was changed

according to requirements* As a whole 15 samples were

selected for grain size analyses* The size analysis was

carried out by a seiving 0^2 i^entworth scale using ASIM

22 cm diameter sieve* In each sample 100 gm sand was sieved

for 20 minutes using Eo tap sieve shaker and fractions ircm

different sieves were collected* The weight percentage

frequency and cumulative weight percentages were computed

and frequeniy cumulative curve and histogramc;es were plotted

for each of the 15 samples* To compute the characteristics

of size frequency dletributlon the parameters given by

Folk and MarA (1957) were used* Out of 15 samples, 10

sasqples were selected for heavy mineral analysis* The heavy

mineral separation was carried out from the fraction next

to the modal class by using the centrifuge method defined by

Taylor (1938)* The bromoform of specific gravity 2*67 as

the separating liquid was used* The heavy mineral crop

was weighed ami permanent mounts were prepared for all the

samples for further mineralogical study*

ACKNOWLEDGEMENT

Bio author is gxateful to Or. Bi^-^ Bhardwajt

D«par1»«nt of Qaology, AyM«U« Aligarh for suggesting

tho probXwi and supervising the investigation* He is

very much thankful to Prof. V»iC. Srivastava, Chairman»

Department of Geology, A.M.U. Aligarh, for providing

the laboratory facilities. Thanks are also due to all

his colleagues who helped him in various ways*

cs ,fV1^

A

Fig.2 5howin3 Lithofacies Distr ibution In Yamuna River Sediments .

cl

cs|

c cs!

^M/Msismm/M

^W^MA

c

A & B BANK FACIES

C POINT BAR FACIES

C H A P T E R - II

IKe lithofacl«8 r«cogni8«d in th« Yamima riv«z

S9dliB«nt8 ar« mainly sandy and aiudcty* each of tiimm is

definad in tazmt of iithology and aedioantary structuraa*

Thasa facias viT9 ax«siinad in ovarbank daposita and in the

channel deposits separaUily (Fi^* 2 AB).

OV£aSAf#; DEPOSITS

1* Sandy Facias S* The sandy facias is made up of

sand bads and present in every trench dug on ^ e banks of

YaiBuna river (Fig* 2 A)« The reaults of the grain size

analyses show that the sand cosipriaing the sandy facias is

not coarse but very fine* The individual sand beds are

25 to 3U era thick* However, the thicker units are also

present* Most of the sand beds ar9 separated by a thin

layer of raud» giving an idea about the varioua cycles of

depositions* The sandy facias occupies the lower portion of

the bank deposits and shows a decrease of grain size

towards the top of the sequence* The primary sediisentary

structures present are crosa bedding* horizontal bedding*

ripple drift cross laminations and wavy l«aination at the

top* The crosa bedding are of planar and trough type* Both

u

Xarg« and small scale cross biding occur in size from

few nm to 40 cm* Bie thickness of sand beds co: prising

horizontal bedding is 2 to 3 m» The coarse sand occur at

the basal part of the bed and coioprised of trough cross

bedding followed by finer material having small scale

cross bedding* ripple drift cross lamination and convolute

bedding in turn (Fig* 2A)* 4o8t of the sand shoiRis a grey

colour with siiea flakes and organic matter at the base* The

sandy fades has been traced up to 2 ksis laterally*

Xnterpretationt

The sandy facias gensrally occupy the lower part

of the bank deposits with 8ilt» clay or laud deposition at

the top* The presence of thick sand beds representing minor

crevase splays or exceptional floods*

Muddy Fades t- Muddy fades is mainly comprised

of silt and clay which is brown to grey in colour* This

fades exhibits rootlets and organic materials with the

occurrences of the sand beds which are 4O-20 cm thick. The

brown grey colour of the mud is because of mixing of organic

Ciaterial with silt and clays* Muddy fades occupies the top

portion of the bank deposits and generally lying above the

sandy fades* The thickness of the muddy sequence is up to

5 IB but no v^«re th«y ar9 greater than 5 ra* A nuni;>«r of

sediBuintary s true tiaras has bean observad in tha E»jddy

faeiaa* Hm^evmr, the siasaiva units are alao preaent* Among

the aedicientary atructuxea are convolute bedding* ripple

drift eroaa laiaination «nd wavy lamination* The convolute

be hiding occurs in t^e upper part of the deposits where the

sediment is clay or silt size and individual units in which

the convolute bedding are foui a ranging in size between

20 to 30 cm* Th9 other prosdnent aedii&entary structure w^ieh

is frequently seen is ripple drift cross lamination

occurring in phase and out of r^aae* Bie individual units in

which this stricture is piresent is 30 to 40 cm tttick* Hie

muddy fades is also charaeteriaed with a decrease in

grain size from bottom to top and generally occurring as the

sheet deposits and has been traced laterally for a conside]>>

able diatance (Fig. 2B)»

In terpre tation t

The sediments of muddy facias have been deposited

from the suspended load after the flood* Ihey can be

interpreted aa overbank flood sediments of minor distribu­

tary channels and the intercalated beds of the sandstone

laay be (Ascribed as minor crevase splays and mud layers

give an idea about the number of flood epiaodes occurred

A '•>

during th« deposition of a particular sediiaantary unit*

POXNT BAR DEPOSITS

Point bars are th« i^tt s»rominent geCMEiorphic

foaturoa of a Bwandoring etr«am and maxioura sodiaontation

tak«ts placa on th« point bars* Tho siza and ahapa of a point

bar is largaXy dapandant on tiia siza of moving stroaffi* In

the BEialler straams point bars are the aienpie depositional

features on the convex aide of the nieanders dipping gently

towards the channel* On the other hand in the large rivers

point bars cosipoaed of the scroll bars alternating with

awales* In ttya point bar ctepoaita sandy faciea and audldy

faeiea have been identified (Fig* 2C)*

Sandy Faeieai- Sandy faeiea in point bar deposits

are exeluaively made up of the sand «fhich ia larger in aize

ae coi (>ared to sandy units preaent in the b«nk deposits.

The strueutng preaent in the sandy faeiea of point bar

depoaits are also larger in size than preaent in the bank

deposits*

The generalized sequence (Fig* 2C) reconstructed (m

the baais of various trenches dug in the point bars show

that the b«ial 4 m thick aequence of the sand is aarked by

the cross bedding* The trough cross bedding of large scale

is th6 co{amon@8t typ« primary s«diiaentary struetura

occurring in eosets and occupies ilia baaal part of the

^int bmr <^po«its. Th@ othar atructteraa praaont ara

planer cross badding* horizontal badding and rippla drift

cross laminations* Tha planar cross bedding generally

overlies the trough cross bex^ed units and at varioua

localities sfid chase two types of cross bedded units ate

separated by an intercaXated bed of horizontal bedding«

Ihe size of the sandy unita corriprising the cro&s bedding

of either types is greater in the basal portion s» coiapared

to the units presents in the upper part of the point bars*

Hie lower 4 m of the sand is isainly represented by the

structures such as trough croaa beddingy planar cross

bedding and horizontal bedding* However* the upper 1 m of

the fine sand is represented by ripple drift cross laiaina-

tions or by oassive units showing general fining upward

sequence* Ihe topmost part of the facias is occupied by fine

silt and clays repreaenting the mud facies of a point bar

depoaita (Fig* 2 C)*

Interpretations

Sandy facies of point bar was deposited vii9n the

channel migrates laterally* Moat of the aand which is prea«it

in the form of cross bedded unite was deposited due to

rdgraticm of sand on the gentler slope of the longitudinal

and transverse bar8» or by infilling of the trough shaped

seourst or by migrating bedforos during the {>eriod of

rapid sedioumtation*

Muddy Faeiets* The overXying 3 to 4 m thick

sequence eosfurised of silt and clay is represented by muddy

facies of point bar deposits* Ihe sediments of muddy facies

are Iwninated and the most cociton sediaentary structures

present are ripple drift cross laminations either in phase

or out of phase and small scale cross bedding of both

trough and planer types* Ihis fMsies generally present as

the thin venear on the top of a point bar a nd lasrk the top

of a genetically related sequence* Thn individual beds in

this facias are IQ to 20 cm thick, ^in the lower part of

the iBu dy facies the small scale trough and planar cross

bedding is observed as overlying on the ripple drift cross

laminationsr occurring in the single sets* The top of tt»

facies is marked by laassive beds which do not show any

sedinentary structure* The total thickness of the mud facies

Show large variaticm and the thickness rnriges between 2 to

3 m (Fig* 2 C)*

Interpretatient

niis facies represent the upper part of the point bar

deposits and show a general fining upward cycle of sedioken-

1.1

tation* Th9 structur* present in thoa diigg««t that most

of th« d«po8iticm took placo by a moving eurront of low

volocity and 8i«p«naion«

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PLATE-I

Fig !

EXPLANATION Cff THE PLATE

Fig. - I Showing rippl© drift cross lasinations in which the ripple laminae are in phase

rig* - 2 Figure showing the in drift nature of the laminae

C H A P T E R - III

SEDIMHNTARY STHUCTUHES AMD FLOsV PATTEIihS

STRUCTIME MORPHOryPE

I1i« river Yarauna* in the area under study displays

a meandering pattern in the plane view (Fig* 1)« The

Rain feature of a laeandering r iver are point bars (deposi -

t ional feature) and scour pool (erosional f ea ture) . This

nature of siraultaneous deposition and erosion maintains the

cieanciering in the channel* Bie point bars build l a t e r a l l y

and downstream across the flood plan «^i le the scour pools

are formed due to erosion on t^e inner part of the loops*

The river Yiuaimna transport a huge quantity of sand» s i l t

and clays* Most of the sand i s deposited as a point bar

deposits while the f iner material i s deposited on bank

deposits* /^ong the most coniuon sedimentary structures

present are ripple d r i f t cross laminations» cross-bedding*

convolute bedding* wavy laminations and massive units

( f ig* 3 and 4)*

RIPPLE DRIFT CROSS LAMINATION

The structure produced by c l icking ripples had

generally been referred to as 'ripple dr i f t cross laminaticms"

li H

tmiter (1963 and X969)» Jopling and vvalker (1968) ,' sup^r-

ituposed ripple laminae in rhyl im" Mckoe (1^5), or

cliiTDing ripple cross laciinations Allen (1971a and 1973a)•

Hippie drift cross l ioiinations are the internal

structures developed as a result of the forward aiigration

and simultaneous upv^axd gro«rth of the ripples* Their develqp-

cent requix^s a continuous supply of excess sedioMint to a

current or wave Eucher (1919)> Heniek (1961), Allen (1963)

and nalker (1963). .ckec (1965) also suggested two types

of the ripple drift cross laminations*

1* Hippie iMiinae in phase

2* Hippie laminae in drift*

in ripple drift laednae in ^^hase* ihm crests of the

successive clioybing ripples lie directly above the others*

Aitnough there may foe a slight shift of the crests that is

always in down current direeticn (ilate 1» Fig* 1)*

In the fieldt the ripple drift in phase are

frequently <^served and occupying the top positions in the

banks deposits as well as of the bar deposits* they do not

sho«v any shifting of the crests and lie directly abo^m one

another* The thickness of the individual units ranges

between 3 as to 6 cm* However» the eraplitudes of the individual

rippl«s is 4 cm and wave langth up to 10 cm or raora

(Plate 1, Fig. 1}«

In the ripple lausd-nation in drift» the crest of the

successive ripples do not lie directly above the others

and exhibits a shifting of the crest in dotftnn current

direction (Plate 1» Fig* 2)* The lacdnae are not continuous«

This type of laminae is developed in an environment w.'hero

the less sediaent is available to a comparatively high

velocity current* G@nerally the stoss side of the ripple la

eroded and lee side is preserved*

on the basis of the preservation of the stoss side*

the ripple drift can be divided into two types*

Type - A • are those in which both sides lee* and stoss are

preserved*

Type » B t are those in which only lee side is preserved*

All the variations exist from cases where the stoss

side laminae are completely preserved through a partly

preserved stoss side into the forms wdth the stoss side

completely absent* In the field the ripple laminae in drift

of both types are observed* they occur mostly together in

point bar deposits and also in bank deposits occupying the

i ^

upper portion. c^n«rallyt they are underlain by a muddy

layer* The thiclcness of the individual units ranges froia

2*5 cm to 6 cm and the forset laminae inclined at an angle

of 13^• The drift laminae of type-A generally pass©8 into

tlte lamination of type-i*

interpretations

Buchor (1919), Heniwk il9i»3b) and Kck«e (1965) have

observed that the ripple drift cross lasninationa are

developed where the excess suspended sediment is conti­

nuously available to a current or weve«which is in turn

deposited above the earlier forraed rippled layer. Field

observations reveal that the ripple laminae in drift and in

phase both asQ developed simultwieously. A slight change in

the depth of flow» supply of sediment and in the velocity

of current results in th9 different arrangeraent of the crest

of the rippled layer. The continoous supply of the sediEients

helps in the fonaation of ripples in the sand which irdgrate

continuously without makirg any permanent structure« are

burried by suspended sand and preserved to give rise a

series of superiisposed ripples. They may developed in phase,

if the velocity of the water is less and depth is more or

in drift if the velocity of the prevailing current is

slightly higher and depth is less.

Rippl.« la> ina« in phase aire deposited v/hen th«

rlppXo foxi ed in sand by wm® ara not eroded and both $toss

and lee sides are preserved as they were formed originally,

before starting of a ne^ cycl@t the suspended sand is

deposited taui eompletely covers the earlier foriaed rippled

layer without shifting the crest of the ripples. Coleman

(1969), tUenek and Singh (1962) describes that this

phen<»aena takes place in an environn^nt of the lower flow

regime vvhere the velocity of the prevailing current is

coE^aratively slow*

Jopling and talker (1968) expressed tlw origin of

the rippla drift cross latrdnation in t ria of the suspensions

bed load ratio* They concluded that if the nuch sediment in

suspension is available there will not be erosion of the

stoss side of earlier toxm96 rippled layer artd v<iixi completely

be preserved under a cover of sand* This overlying sand is

again rippled and shows a slight shift of crest in down

current direction to represent the ripple drift of type-A«

un the other handp the ripple drift cross lamination of

type^B are formed when the ratio of the stispended load/bed

load decreases* Unoer such conditions stcos sidas of ttiO

ripples are eroded away before they aro preserved*

PLATE-2

Fig.— I

Fig— 2

EXPLAMATION OF IliE PLATE

F i g . - I Planar c ross bidding bounded by ho r i zon ta l bedding bo low and i^ov^^

Fig» - 2 figux® shomlm tlio trough cross bodding occuring in cosets

f^ .«.

CBOSS BEDDING

A QXOS9 b«d is defined as a single layer or a

sirtgle sedimentation unit ccmsisting of intezt^al laoninae

(forset laffiinae) inclined to the principal surface of

sediioentation otto (193&)* iXkee and weir (1953) defined

the cross bedoingi as **The arrangeraents of layers at one

or more angle tc the original dip of the fomation" and

the ccosL betiding unites as ona with layers of deposits at

an angls to Uie original dip of the formation*

!• Planer Cross Beddings- A cross bedded unit v hose

boundli^ surfaces are more cr less planar surfsees.

2* Irougtt Cross Beddings- A cross bedded unit whose

bounding surfaces are trou^ shaped*

un the basis of theix thickness they are further

divided into two typest

1* ctoall Scale Cross Beddings- In which the thickn^s

of individual units is less than 5 cm.

2. Large Scale Cross Beddings- The thickness of the

individual units is greater tiian 5 cia* Ihey laay either be

trough or planar* Both types of cross bedding f very much

common in Yamuna sodiswnts.

PLAJtim CBCtSS BEDDING

Planar cross bodding is very ouch ccmoiKm in Yamuna

8ediA»nts and occurring both in cosats a« well as in

inciividual bads. Thay ara ciostiy overlain by ripple drift

cross laminaticms convolute bedding or by massive units

(Fi9«3 and 4), The thickness of individual unit set

ranges be^een 3 cm to 30 era* But generally they axe 2& cm

thick* The thickness of individual Iseiinae in small scale

cross bedding is 2 m^ to 3 isca with an inclination of 18^ to

the basal surface while in large scale planar cross bedding

the thickness wid inclination oi laiainae is greater. The

individual units are 3 to 5 cm thick and lamin^Mi inclined

at an angle of 30^ (Plate 2, Fig. 1).

Interpretations

Planar cross bedding are formed in different ways,

Allen (1963) concluded that the planar cross bedding is

deposited by the migration of straight crested parallel

symmetrical xippios ofid the thickness of the individual set

is controlled by the araplitude <^ the ripples concerned*

Exceptionally thick coluon of the planar cross bedding tjem

u ••)

deposited as a result of acretion on oblique ot longitudinal

baxs* However* Harms (1975) described theia tc be foriaed by

the ndgration of sand waves under unidirectional flow.

The planar cross bedding of large size in the present

area seeam to have been <^poeited due to the migration of

sand on the gentler slope of the longitudinal and txansverse

bars* The sand taigrates continuously in the fona of climbinsi

exceeds the gentler slope and sand starts slipping d<Mn on

the steeper slope or on the (Wala»ehe face of the bar

concerned. lh» aaigrating sand is deposited in down current

direction parallel to the slope avalanche face and latter

is preserved as large scale cross bedding* /hile the sniall

scale planar cross beddinq is produced due to n^ration of

straight crested sraall riindies or in other v«>rds v e can say

that the size of ripple controls the size of cross bedding.

Reniek mitk Singh (1980) concluded that small scale cross

bedding is formed by the niigration of current ripples*

THftOUQK CfiOSS BEDDINQ

Trough cross bedding is frequently encountered in

sediments of Ymiuna river in bank deposits as well as in

bar deposits either in coset or in single set* In a section

transverse to the direction of flot t observations reveal

that the sets are arranged in a nested pattern in which

each set ie bounded below by a concave upward* eroeional

surface to i~/rdch t\w laioinae are approximately parallel*

n the ott^r hand» the boundaries of the set® are parallel

to the flo\.' direction* if they are observed in a section

parallel to the flov./ direction* Bie infillod trough may be

eyoTuetrieal or aeeymetrical and the thickness of the

individual yets are variable in their size and geon^etry.

Trough crusa bedding occurs frequently in the area

und@r study gonerally overlain by ripple drift cross

laainationt horizontal lamination and mud layers (i ige* 3

and 4 ) . Imjividual units are 2 mm to 40 mt. titick as the

large scalo trough bedding is concerned while the small

scale cross boading is 1«5 cm to 5 era thick* In large scale

trough cross bedding the inclination of the lamination sets

is of uniform thickness ami is gentler in the upper part and

steeper in tite lower portion of a single unit* They all dip

in d<mnstreaBi direction and the inclination of the laminae

it 5^ to 25^ and the forset laminae are f ew EK. to 2 cm thidc •

On the other hand in the snail scale trough cross bedding

the laminae dip in down current direction with an inclination

of 3^to 15^ «id the individual forset laminae are few to

0*f> eia thick (Plate 2, Fig* 2>*

('•:

Xnt«rpr«tationi

!ti@r« is a gen&ral agreanient araong sediie^ntolegists

that tha large seal® trough cross boduing are deposited by

infilling of scours* Those result when piles of brush or

stumps becoroe stranded in shaXlc ' streams and subsequently

filled by sandi) Allen (1963, 1965c) • Harms and Fahnstock

(1964) and Land and Hyat (1966) concluded that the large

scale trough cross bedding axe forised by the infilling of

large trough shaped scours by nsigrating dunes* Jopling

(1963* 1965) was of the opinion that the large scale trough

beddif^ i© fon^d by infilling of scour pockets with lee

face of advancing dunes* Jopling (1963) and Harms, @t al

(1963) accounted tor t^e aechanism of the infilling*

According to th ra the infilling of the scour pocket and the

develoi:^ent of trough cross bedding is favoured by a

relatively high velocity and a high dspth ratio (shallow

basin)* However* Sundborge (1963) related ;hese structures

to the tranquil Horn rather than high velocity flow* Allen

(1963) believed that the small scale trough bedding were

developed by forward migration of the lingoid or lunate

asymmetrical ripples* Field observations revealed til\at the

large scale trough cross bedding in Yamuna sediments \*wre

SiOstly developed as a result of scour filling* These scour

are generally developed in mott of the river bed due to the

PLATE-r3

Fig. _ I

Fig. -2

EXPLANATIOM ( IHE PLATE

Fig* • 1 Gonvolut« bedding •> both troughs and crcistG axe rounded

Fif|» - 2 Convolute bedding - crests are pointed and troughs are roumled

erosion by a high velocity current* The small scale

trough cross bedding is produced by the migration of the

small current ripples and their shape and sise are contro­

lled by the type of ripple producing them. The sfaall

trough cross bedding is produced by small lingcid ripples*

They may also be developed by the laigration of ripples in

which one ripple clings onto the back of ^ e next ripple

downstream*

catNoWTE aBmim

B)e convolute bedding are the internal structure in

which the laminae seein to hove been folded usually with

broad syncline and narrow anticlines* In Yamuna sediments

two types of the convolute be>uding were observed in v^ich

the either both trough and anticline are broad or with a

corfibination of sharp and broad anticlines (Plate 3» Figs* 1

and 2)* In a tiuree dimensional view convolute laminations

generally appear a s a more or less regular pattern of synirae-

trical or inclined isolated cones separated by depressions*

The laminae in convolute bedding may be intensively folded

but they always are ccmtinuous*

Originally the term convolute bedding was proposed

by Kuenen (1932) to describe the ** laminae showing destruction

f-4 !••

that gradually incraasec up«»ard to intensiva but rathar

regular fold and then dies out gradually*** In geologic

literature the convolute bedditm is known by different

names. Fearnsides (191u) described as curled bedding»

ivdglorini (195a) m crinkled bedding, Richi (1950) as

intrastratal contortion, Ksiazhiewoz (1951) as slip

bedding. Teen Haff (1956) as ccmvolute lamination* K.unen

(i953a)t Potter and Petti John (1%3) defined the convolute

bedding » internal struc^ire showing marked crumpling ox

complicated folding of laaiinae of rather well defined

sedimentation unit*

The convolute beddir^ in the field is generally

observed in fine sediments occupying the top portion in the

bank deposits* These generally underlain or overlain by a

massive and undisturbed layers (Fig* 3)^ however, soaetiiaes

show an erosional upper contact (Fig* 4)* On the basis of

the nature of their axial planes they can be divided into t»

two types •— Type A and Type 0*

Type - A I- The convolute landnations in which

the anticlines and troughs, both are rounded snd axial

plane is vertical (Plate 3, Mg* 1)« The anticlines are not

so broad and rounded as the trough* The thickness of the

individual unit of the convolute bedding ranges from 10 cm

to 30 cm* The individual laminae show large variation in

f^''}

and alternato v ith dark and JLightar colourad laminae*

Typa - B •* In typa~B« the axial plana la

inclined dipping in dovm current direction (Plate 3> Fig«2).

The laminae have been folded intenalvely and show no Blgn of

faultily)* The troughs are broad and rounded and the

anticlinea Are sharp and pointed. The individual units of

convolute bedding ranges frooi 10 cm to 30 cm in thickness

and generally overlain by a mudd layer or by ripple drift

cross laminations (Fig* 3)*

Elnsele (1963), Wunderllch (1979) and DeBoer (1979)

described the convolu e bedding from the present day @

environsient of tidal zone deposits* Oeober (1979) also

described them from intertidal shoals* In fluvial environ­

ment they are c oijnonly found in flood plain deposits and

even in upper point bar deposits Mckee (1966) and Coleman

(1969). Coleman and Oagliano (1965) reported them from the

natural levees of distributary channel of the mlsslsippl

delta*

interpretation!

The convolute bedding is a complex and polygenetic

structure* Howaver» irrespective of dlffounces in interpre­

tation and diversity exhibited by the structure Itselft It

appears that l^a struMStur* ariaea in raeponaa to a vaxtieal

pattarn of {urtssura acting upon easily daformad plaatie and

laminated sediiMHit. SeteraX explanation have been proposed

for the gienesis of eonvolute bedding* Kuen@n (i953a)

believed that convolute bedding developed from the defonaa-

tion of the ripple marica* iiiilli«B (I960) auggested that

convolute beddlt^ is produced by differential liquefaction

of a sedimentation unit* Lateral intrastratal flow ci these

liquefied units produces contortion* Mckee et al (1962) and

i4ekee siid Gold Serg (1969) developed eonvolute bedding in

laboratory by placing differential load fxcm above and

concluded that vertical forces reaulting from overloading

are important in the generation of convolute bedding* Sander

(1965) .ias of the opinion that Uie convolute bedding is

produced by the action of great shearing on an cohesive

sedlioent layer* v unci rlich (1967a) believed that the

convolute bedding resulted frocsi the liquefaction of the

eediiaents* The liquefaction is achieved by overloading» by

aeisciic tyaves or by other shocks cauaing a disturbance in

the sediaent packing* Lava (1974) and Allen (1977) suggested

that within a layer with an initial stable denaity gradient

the process of liquifaction and reaedicientatifm into a

lighter packing might result in a short lived denaity

instability which could be relevant to the formation of

convolute lamination* Lave (1975) regarded the convolute

PL A T E - 4

Fig I

F,g._ 2

EXPLANATION OF TliE PLATE

Fig# - i Horizonta l bedding

Fig* - 2 Massive u n i t ov@rlyir^ convolute bedding

f", '

boddlng as th« »vat«r Escape structura producsd during

dtwatorlng and consolidation* Reneik and Singh (196Q)

descxibad that under the action of localised differential

forces a hydrostatic sediotnt layer is throvnn into

convolution prociucing convolute t>edding» Hoivever» Collinson

and Th<»kpson (1982) regarded that the convolution involves

the plastic deformation of partially liquefied sedisHint

soon after deposition. The literature available reveals

that the convolute bedding may be developed in several ways*

But in the laresent area it looks that it has been developed

by escape of water after the exposition of the sediismts*

or by differential loading*

HmiZmVAL BEDDINQ

Horizontal bedding is made up of parallel and aliaost

horizontal sand layers* Each layer may range from few imx to

1 CIS* Hanas anc Fahnatock (1965) described that horizontal

bedding consists of the tabular sets of laminae in sand

s i z ^ siaterial within which the laminae are horizcntal or

nearly so* The sand is well scorted and laminae are excep­

tionally thin (appr* 1 mm)*

In the field t horizontal bedding is observed mainly

in bank deposits and also as pockets in the point bar

deposits* The horizontal nature of the bedding has been

ti t.

developed due to deposition on an earlier hoxisontal

surface* The horizontal bedding is overlain by large acaXe

plan ir cross bedding and underlain by finer material* Most

of the units cos^^rised the sandvith .ica flakes and some

organic tiiaterial at the base* The units are 30 era to 1 m*

thick although some exceptionally thick units are also

observed ranging in thickness up to 3 and 1/2 loeter*

noBiBtimeB the laminae show v^uriation in colouTf alternating

light and dark bands and are 1 era to 4 cm thick (Plate 4,

Fig. 1).

Interpretations

^imon and iiiehardson (1962) concluded that the

horizontal bedding i as developed in the upper or shooting

flow regime specially in that part of the upper flow regime

with plane bedfoj^os* Allen (1964) vvas of the opinion that

the horizontal bedding are t e product of high flow regime*

However* Jopling (1964b) proposed that the down current

UiOvement of dunes under essentially steady flow conditions

lead to the formation of t e horizontal bedding*

The mode of the deposition of the horizontal bedding

is not well understood* Kumar and Singh (1978) described

that horizontal bedding inay develope in two ways and can be

divided at follovt«t

f}

!• Horizontal Bedding of High mexgy (upper flow regime)t-

This type of horizontal bedding occurs in seferal deciraeter

thick iaiaination is very fine but rather indistinct. They

are associated «vith parting lineation and represent a p-

product of deposition under high velocity currents*

2* Horizontal Bedding of Low Energyt- This type of

horizontal bedding is produced as a result of deposition

ttom suspension cloud® diue to reduction in the turbulance

of flew* In such cases lamin«i;ion is fine to thick and very

distinct* Differentiation between adjacent laminae is well

siaxked*

^AVY UUaNAriOfd

Mck^e anc keir (1953) «iS0d the term lamination for

those bedding or layers whoso thickner s ranges from 1 lm

to 1 era* Pettijohn (197S) f-ar the structures produced by

rippling* Heinak and Singh (198U) used the terra wavy

bedding for the catitinuous alternating mud and sand layers*

The individual seta of la inae are developed in very fine

material such as silt and clay*

Wavy laesination in the field are observed in point

bar deposits as well as in the bank deposits and occupy the

.•i J

upper portions of the sequenco (Fig«« 3 and 4) . The

individual units are 5 cm to 20 eta thick with &n aispXitud«

of 3 or 4 cia. Th« individual X«bin«e ar« alternating with

darker and lighter colours having a thickness of 0.5 ma to

2 VSBlm

Interpretation:

The literature available reveals that the wavy

laciination i s developed v4ien the deposition of the fine

material take place in a calm and quiet environioent* s the

flood receeds iiie velocity of the tran8|>orting aediura

beccraes nearly etraight and i t l>eccNRU(8 unable to transport

further and deiNMiited and becccae sett led* the pest^-depesi*

tional condition disturb the previously deposited lacdnation

and thus wavy lamination i s produced*

The term massive bedding i s 9<»3stises used to

describe taote or Je u& homogenous looking sedioents and

apparently do not show any v is ib le structure* How#yerf they

may show internal lamination i f they are exposed to x-rays»

Hamblin (1965}« The massive bedding can be developed in fins

sand as well as in coarse grained sedimmmts* The massive

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uni ts ax« coBQ^iised of s i l t , fin* sand M%6 SOB« post-

<i«}>oaitional products l ike clay ba l l s and kankairs* Itie

thickness of th9 individual beds irango batv^aan lo to

30 em and shc^s l a t e r a l variat ion in t he i r thickness for a

consiaaxa£>l€! distance* Ihey occupies the top portion of the

sequence and occur as the separating layer (Plate A,

Fig , 2 , 3 , 4)*

Gonad of the oassive beds are also produced by thm

strong Oioturbation act iv i ty* Ani&als also play an

important rola In the developiacmt of massive bedding by

destroying the prioiaxy layering of sedlcmnt and thoroughly

Lix t em up to produce aiassive units* j*erner (1963) found

tha t loany {Aicro~organisi& living in the pore spacer of

sediaients can destroy the primary bedding Mid produce

hoiaogeneous looking sand* Massive bedding may also be produced

when water i s dxainad out during ec^^action or v^&n genera*-

t ion of gas bubbles moving upvvaxd causes destruction of

bidding Forstner ot a l (1965). Eenlek and Singh (19@0)

described the massive bedding as the oiixtuie of unsorted

sedisMWit without any well defined s tructure*

¥Lm PATTERN

Xh< direction of current flow existing in an area

can be deterndned with the help of systematic measurMoent of

cross beciaing ancl oth^r current generated sedimentary

etruetures* Further* a detailed study of these oieaeureiiiefite

makes possible to determine tbe conditions prevailed during

the deposition of the fSomation and the existing flow

patterns*

Hie present area under study was divided in to s ix

sectors (A9 B» C* Dt £ and F) ^kd each sector was divided in to

several loca l i t i e s to determine the local flow pat terns*

AS a whole the three hundreds measuriMBent of the cross

bedding aziuiuth were taken and the data was plotted in t^e

form of c i rcular histogram (Fig* 5)«

The vector mean (QV) arid vector iiagnitude CU<) for

each sector a nd each loca l i ty v^re calculated separately by

follov^ing vector suisnition method (Curray* 1956). The

r e su l t s are presented in Table •

Vector Mean (QV) t - the table-1 shmvs that the

QV values detenuined for tlie sectors as vwll as for the

l o c a l i t i e s are not saiae* The QV values for the a l l aectors

ranges between 13S* to 225® (Table - 1)*

Vector Strength (L^:) t - Vector strength i s a lso knomi

as tite consistancy r a t i o . The vector strength was calculated

a t the local i ty level as well as at the sector l e v e l . The

M vaJluis deterialnecl for aXl sector ranges b«twd«n

67«71;w to 87«3^:« Hoimv9i^, at local i ty level i t ra^ee

between 83.66;. to 99*9%> (Table - 1)«

Variance (S^) i - The variance of the foreset dip

aiimuth varies at the sector level as well as at the

local i ty levels* The S^ values deterrained for the a l l sectors

ranges between 762.22 to 2431*19 (Table - 1) .

Table v 2 7 Si£Q f requency D i s t r i b u t i o n ( P e r e e n t ; of Vaimina Sands*

u u a n U t v Dianieter i n PHI (# ) S c a l e A J - I Q I U ^ ^ ^ ^ ^ ^ ^ ' III r I T -- - • - • • - • - - - r - - - • II Til I I I I I

^„"T*" t a k a n lUuh f^^sh Moch i esh lk&&h ^iesh m&h iA&Bh num©©! i n gfcis. . 5 to 1 ,0- 1 , 5 - 2 , >- 2 . 5 - 3 . 0 - 3 . 5 - > 4.0

I .O 1.5 2.W 2 . 5 3.U 3 . 5 4 . 0

1 l o o O.UU 0 . 0 0 O.IB 4 . 9 8 62 .92 14 .77 11 .50 5 . 5 1

2 IOC 1.99 5 .88 1.99 1.857 3 .163 3 .954 lQ.905 70 .224

3 100 0 .036 0.S76 2 .536 43 .492 33.439 15 .83 3.674 2 0 . 4 7 1

4 10. O.C/4 0 .041 0 .271 2 .599 48.4153 19 .248 17.17 12 .148

5 IOC 0.052 0 .195 0 .822 1.296 8.555 22 .913 46 .744 1 9 . 3 9 1

6 lOCi 0 .008 0.072 0 .34 0 .838 4 . 2 4 4 .692 10.904 7S .S85

7 100 Q.004 0 .038 0 .57 1.238 10.335 26 .687 40 .677 2 0 . 4 5 1

8 100 0 . 0 0 0 .024 0 .026 0 . 0 5 2 .336 3.764 9.866 B3.432

9 100 U.0II5 0.08*» 0 .374 0 . 5 4 3 6 .452 24 .739 40 .545 27 .202

10 l o o 0 .004 0 .004 a .043 0 . 9 8 1 17.839 19 .348 30 .546 3 1 . 2 4 1

11 100 O. lOl 0 .582 4 . 7 1 5 13 .042 5 7 . 9 5 15 .043 6 .448 2 . 0 9 1

12 100 Q.OC' 0 .002 0 . 0 0 3 0 . 7 6 0 .412 1.216 4 . 8 1 9 3 . 4 9

13 100 0 .05 0 .203 3 .137 11.166 52 .097 16 .32 8.87 8 . 1 5 1

14 100 0 . 1 1 1 0 .133 0 .25 2 .624 38.714 12 .443 10.399 3 5 . 3 2 1

15 100 0 . 0 7 0 .226 1.136 1.662 8 .369 21 .219 3 9 . 8 2 6 . 9 8 3

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CM • CO

CO • CM

<n •

CM

«

^

«n •

CO

CO

• CO

3

• ^ CM CO in CO 0» O •-« CM CO t*" ^ <^ »4 11^ #4 ^

C H A P T E R - IV

GRAIN SIZE ANALYSIS

£»ize distribution of sodisiontry particles has

be&n described in several ways and many sediioentologist

have mads useful contributions to decipher t)vs environ­

ment of the sediiiientry colous.ns* Task (1932) established

a system of iseasureis^nts based on the millimeter scale*

Kruasbein (1934) established the system of phi notation in

which 0 equals the Ic^ of the ratio of grain diameter

(car..) to standard diameter (nsi). itere» following Folk

and iiiard (1957) the s ta t i s t i ca l parameters of yat>una

sediments were calculated and the results are shc^n in

Table 2 ami 3« The grain siM analysis of modern sediioents

i s of great importance as i t provides informations

regarding the affects of ths known processes prevailed

during their deposition*

The Table 3 indicates that the six samples out of

f ifteen contain maxirauoa sand in 2*5 to 3p class and their

weight percentage ranges between 38*71 to 62.92. The other

four samples contain maximisa sedimMut in 3*5 to 40 c lass

and carry 39*8 to 46*77 percent of the sediment by weightt

Howevert maximum sediment i s present in > 40 class with

31*24 to 93*49! . of the total by weight* The data was plotted

70

60

50

40

30

20

10

z UJ

o cc UJ a.

o

LU

5:

80

70

60

50

40

30

20

10

Q m •.— Ln cs i.n n ip vj- vj-

l i t I t I 7 u o m LD CN5 lo m in -J- ^

CM ( ^

CM

M I I I I I I K ~) in '- in c^ in n .n O in o4 in ro in

D I A M E T E R IN P H I ( < / ^ ) 5 C A L E

Fig.6A Hrstogrames Showing Mechenical Composition

Of Yamuna Sands.

t— z: lij u a:

a.

o

UJ

%0

70

60

50

AO-

30

20-

10-

70

60

50

AO

30

20

10

O Ln"— ' i ' CM in n lO VT <r •| I T I <<J I f , A o i n ^ in I tn I ,A I

,-^ (Nl CN ro ro

o to

o i n

D I A M E T E R IN P H I ( ( ^ ) S C A L E

Fig.6 B — H'istogrames ShowingMechanicdl Composition Of Ydmuna Sdnds.

2:

U D: LU Q.

X

o LU

5:

70-

60

50

^0

30

20

10

^^\^c ..^ Q IX)''— l o c M l o n uf>vx<j -

, • ^ rv) &i

' ' i I A M i n »- in (N i-i> ro |A .

o ID '— Ln cN) in ro in ^T - r CM . ^

o in ^ ^ A

D I A M E T E R

CD LD in CN ip ro in A

IN PHI i^) S C A L E

Fig,6 C Histogrames Shov/ing Mechanical Composition

Of Yamuna Sands.

LU

O

cc: LU Q-

o

UJ

90r

80-

70-

60-

50-

40-

30-

20-

10-

o in "— ip CM ip ro ip vj -<r '^ <>i &^

fi- C<J rt ' ^

D I A M E T E R IN PH\ ( ( ^ ) S C A L E

Fig.6 D— Histogrames Showing MechanicalCompos'ition

Of Yamuna Sands.

z o

a

o

Lu >

3

5 «) 1 - 5 ^ Jo 2 ^ S5 3% 5tr

PARTICLE SIZE IN PHI( ^ )UNIT

Pig.7—Cumulative Curve* Showing Mechanical Composrtior Of Yamuna Sands.

r\ )

in the form of Histogrames and cumulative curves

(Fig&« 6 A^D and 7) represent the average mechanical

composition of the sac^lae* tAoBt of the histogrames show

a unisiOdel seciiment distribution except two samples

repretenting a blraodel distribution (Fig* 6 ABCD)* The

graphic csean values calculated tor all samples range

between 2.8 to 4«1&* uf the fifteen samples» ten sar ples

are ii^derately sorted, three samples are very well sorted

and the remaining two samples are well sorted* The

frequency distribution in five samples is very negatively

skev^ed, four sacaple® axe very positively skewed, three are

nearly ey®:.etrical, ti»Q are positively skived, while only

one is negativ&ly skewed* The graphic kurtosis values show

large variation* Of fifteen sasiples analyzed, five san^lee

are very leptokurtic, four are very platykurtic, two samples

are i esokurticy two saiaples are leptokurtic while one

sasaple is extremely leptokurtic and platykurtic respectively*

^ E ^^^ i ^ ^ k ^^^ ^^^ r"^ r^^ r™' ^r f"~ f ^

W iv 4J M I - C ^ W - 4 0 ^ t f i t i ^ ( j d t O

ro K> to I M I I I c.) ro »- i i I lo

I - I H * ! * . ! I W H - t O M N J l I I -

U W t O P O I - O i U f o r o t O t o H * » - 4 ^ U >

CO C*> 05 <l I - t t lo ^ - c

M O > N > 4 ^ . ^ ' r O M r O U t - ' » - < C a U I - « ' > 4

i <o i t I c^ I Ci I I I I I i

I 0> -^ i <: I CO Cx' M H» I K> I K* to

t i ~ > i ^ u i r o H > i I . ^ o j i - « M w o T

w M ^ - • ^ - « » ( A ^ < A > ^ - • l » ^ i I » - ^ ^ ^ ^ ^ > { A J

H* N3 fO fo fr- * - I I i I I I I I K>

t O » . . | » - ' H > | | | | t | i l t l

i i r o H > i c ^ ' H ' r o i t I I I I I

r o t - t i i i i i i i i i i u ) i

K > K > M l r o I M h - M i A J M M t O ^ k K )

( ^ C N I M O J 4 ^ U i t ; i O < > 4 ) k K 3 ( O C > > & J U >

^ - ^ 3 * ^ ^ ^ ^ ^ ^ « • l i i i M M M r o

Plagioclase

Microcline

Kyaalte

Garnet

Tourmaline

Hpidot

Zircon

t i io t i te

Hypersthane

S i l l imin i te

Hutile

<»4Uscovitd

Zo i s i t e

Mornblende

Opaque ivilnerale

Rock Fr&gi&ents

1 o~ © »-o o ^ •0 § •* <• 1* o 9 •• •o o H O 0 9 r C

•<

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1 Ji.

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O H>

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1 9 0

0 e» I C9 •

C H A P T E R - V

i aNEHAL CaViPOSITlQN

tlft@en sasipies vtere analysed to detexmlne th«

mln«raloglcal cotaposltion .f tho Yafiiuna sand* The

raaul ta are sr>o«m in rable«^. The min«ral8 pr«a@Rt ara

feXspartpiagioeiaaat a ic roc l ine , kyanlto* 8il l i ininite»

rutiXe> hyparsthanat apldot* sircorit touriBalina» garnat*

i u8covlte» 2oi8ite» a t e . Apart fxKm thata silnaral soma

opaqua fainarals and rock; fragoanta ara also praaant*

QU/itilZ ~ fho riiinaral occuxs as aubrounded to subangulax in

outline» Hovvever, some roundad gralna are also present ,

fhe surfaces of the gralna are e i ther smooth or fractured*

The colour of the grains i s l igh t grey* or pink* The

colourless ^ a i n a are also eoGBiaon* Under crossed nlcols

they represent b r i l l i a n t interference colours. They

generally show wavy extinction but the grains showing

s t r a igh t extinction are also found* The inclusions of

ru t i l e» zircon* apat i te* and opaque ininerala are present*

irELSPAtiS " IWo types of felspars have been ident i f ied

l .Plagloclaae S-> The otineral occurs as prismatic or

subrounded grains with charac ter i s t ic lamellar thinning*

PLATE 5

7

* -

8

I 10 II 12^ 13

EXFLANATlOri Oi HIE PLATE

Fig» - I quartz - subrounded to round©d grain*

Fig» •« 2 Kyenlte - subroundc-d ©Icngated ant rectangular in outl ine ^hcmitig ci®avag©8.

Fig. - 3 Oarnet « subangular to subrounded and hae high relief*

Fig* - 4 Tounoalir^ - <^rismatic c rys ta l

Fig . - & Zircon - ©uhedral form long cyl indr ical

Fig» « 6 Muscovite - PrisKiatic grains with subrounded outl ines•

iig» - 7 Biot i te - long prismatic c rys ta l v^'ith broken end^«

f i g . • 8 Hypersthene - Long prisiaatic crys ta l

Fig» - 9 Si l l imini te - Long cyl indr ica l with curved outlines.»

Fig* - 10 Hutile - Prisiaatic form and shcming dark boundaries•

Fig* - 11 Zoisite * subrounded to rounded grain

Fig* - 12 Hornblende - Elongated platy or lath shaped

Fig* « 13 piagioclaee - Prisinatic subrounded grains*

'ill

The colour is gr«y or a variety of grey colour (Plate 5,

Fig, 13),

2» Mcrocllne S- Mlcrocline occurs In the fona of

prismatic and rounded broken grains. Ihey are colourless

or jrey coloured and representing cross Hatch twinning*

Ki^^JtiE- Kyanite occurs as cylinderical prismatic grains

with rectaiHJular outlines* Majority of ijie grains is

colourless but s(»se grains have a light pink or blue

colour* Ihe coloured varieties are weakly pleochoric and

showir^ inclined extinction* The grains show two perfect

sets of cleavage* Relief of mineral in high (Plate 5» l'ig*2)*

QAriiCT - Garnet is the cosiaonest aineral in Ywmina sand*

Beside the coloured varieties the colourless grains are

also represent* l.o8t of the grains are brown to pink coloured.

Ihe grains are subangular to subrounded in outlines* The

mineral is isotropic (Plate 5, Fig* 3)*

TQUiivtALlNE - Tourmaline occurs as prismatic euhedral to

subrounded grains with inclusions* The colour of the grains

is pale green* pink and show strong pleochorisin from pale

green» pale bro«m to dark green or dark brown* Ihe relisf

'4-i

is mod«rat« and extinction is parail«tl (Plate 5» Fig. 4 ) ,

EPIDOT - Th« caineraX occurs as prissiatie grainf the grains

are angular to rounded. The colour of the grains is pale

green. HovrnveXf some of the grains are colourless. The

coloured grains show pleochorism frc i pale green to

pistachio green* The relief is moderate to high*

ZIHCUH " The grains are 8ui>rounded ixt rounded* euhedral

to subiiedral colourless and of light pink coloured. The

relief is high and extinction is parallel. Sosie of the

grains bear inclusions (Plate 5» Fig. 5 ) .

MUSCOVITE - The grains are long cylindrical, rounded or

flaky. The mineral is colourless and transparent (Plate 5,

Fig* 6)«

BIOTITE * The shape of the grains is prismatic or sub-

rounded with irregular outlines* The colour is pale brown

or greenish grey* The basal section show weak pleochorism

in shades of brown. The flakes of uiotite bear inclusion of

other minerals (Plate &» Fig* 7)*

(lYPEHSTiiENE •> Ihe raineral occur as the prismatic grain

displaying Pleoehorisai* The grains are greenish yellowish

'A

OX girednish brovm* Cleavage is perfect anci extinction

is straight (Plate 5» Fig* 8 ) .

SILLIlvtl^aT£ - Xhe grains are Icmg cylincirical or prismatic

with curveci outlines* They are light yellow or colourless

and show nK>derate to higti xx'lief• The extinction is straight

(Plate 5, fig* 9)*

AUTILE » Hutile occurs as the brisk red or yellow in

colour with dark boundaries. Ti\9 grains are subangular to

subrounded in outlines* The relief is high and show a

parallel extinction* The Pleochorism is vtwak (Plate 5» Fig*ie).

ZOISITE " The grains are prismatic und show two sets of

cleavage* The coloyr is reddish to brownish green> under

crossed nicols it shows deep blim interfer<mce colour

(Plate 5, Fig* 11).

HuHNBLENDE -> The mineral occur as elongated platy or lath

shaped. The colour is dark green* brown groen and black*

Die grains show perfect cleavage* It displays oblique

extinction and pleochorism (Plate b, Fig* 12}*

OPAC^UE MINERALS « The minerals which remain dark even in

plane polarised light are said to be opaque* Following

opaque varieties were observed!

! • XU4EN2IE -> Ihe salnexal i s opaquo in plain pclarisad

l igh t and occurs JB roundftd brokan fragmants* Under

atrong ral lacted l igh t the rainaral ahcma a dark purple

colour and subtoataliic lusture*

2 , t»iAGMHTIT£ "> Tha grains ara octahedral t r iangular and

6MOW broken i r regular outlines* In reflected l ight* i t

shows a Dluish grey colour and a e t a l l i c lusture*

3* HEAivlAIITE - The grains »^B rounded to aubangular in

outline* In reflected l i g ^ t they show a cherry f^ to

reddish colour And submetallic lusture*

The rock fragments are c^ sandstone, >hales, quartzite»

schia t and gneiss* 1Rie grains are mostly angular and show

large variation in the i r sizes*

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V C H A P T E R - V I

FLUVIAL MODEL

Th« various typ® of f JLo r«9im«® and th«ir primary

sodifiiwntary 8tru6tiar«$ can bo used to dttfimi tha flov^

raod«i of a riv9f* Ali«n (1963) ffi«d« a diroet att9n.pt in

intorprtt lng a Davonlan firming upwarci cyeiotham in tarns

of f iow ra@iii»i tfhicii providaa usaful knov9l«»€iga to under-

stamS the f luv ia l oM dal* Hare art attempt has bean

made f o r eona true t ing a f luv ia l model of a meandering

r iver which may be useful in sc lving the probleB» of the

SMoe environnenta• To develope a generalized f l u v i a l

s^odel a to ta l of twelve se lected treivshes vmr^t examined

both from bank deposits and point bar deposits (Figs 8« 9)«

Th9 trenches dug in the bank deposits are characterised by

a finnintj upi ard sequence ^ ith large sca le trough cross

bedding at the base and ripple drift cress laiainationt

convolute bedding or massive unit at the top* The represen*

tative trenches of bar deposits are eiiaracteristically

doniinated by sand with occasional fine sediisents at the top

of bar deposit* The structures observed in them a re cross

bedding cmapriaing sand overlain by fine a i l t and clay

ahowing ripple dri f t cross laminations*

on the basie of lithology and seiiaentary structures

observed, two depositional laedelat Model-A for bank depositB

I ,

and Mod«l-4) for point bar deposits have baon davelopad

in tha study araa (Figs 10 and U)«

/4C)DEL -> A

Tha 9anarai saquanca dv^mlopeti from the study of

various tranehas dug in bank daposlts consist of nlna

units ocfforing In colour, lithoiogy awi sedieientary

structuraa* The lowar part of this modal is raprasanted

by a thick COIOUKJ) of larga seala trough cross badding

followed by larga scale planar cross baduing both eon^jrising

comparatively coarse fiand. .Abcva this ic a thick saquenca

of horixontal baddlng ccMsiprisad of sand than small scsia

cross badding followad by a bed of rippla drift cross

laminations over this lias convolute bedding ami finally

amssiva units co!s$»rising imjd* Although, inassiva units are

encountered evan in lower part of sooa of the depoaits but

not frequently* occasional occurence of wavy lamination is

also encountered in the upper parts of the bank deposits*

The organic matter and rootlets intercalations are observed

generally in them* The grain size analysis of tha sediments

indicate that the sequence startsw ith coarse grained

sedlBients and ends with laasalve clays in most of the

trenches* in this way it can be astabliahed that a finning

upward in tha size of sedlauHits occurs throughout the course

^6!

of rivor* fhe pxrestnc® of the different structures in the

sas^ sized material in<^lcate$exlsteiK;e of different flow

regimes during their deposition* The presence of large

scale cross bedding in coarse Sand is suggestive of

high velocity of current which reduced Its intensity

upward and resul s in giving the staall scale cross bedding*

un the other h«nd» ripple drift cro is lj»&inatlon in the

upper part con [>rlsed of fine material Indicate the further

fall In the velocity of the current* i hile mud layers at

the top representing nearly stagnant .iater condition

possibly after flood time* The convolute bedding is not a

result of the current activity and developed as a result of

post depositional processes*

This model represents a upv^ard decrease in the

grain &lze» scale and type of sadliaontary structures,

indicating a change in*e doposltlonal environment from

bottom to to.* It fvrth&T suggest that various cycles of

deposition representing finning upward @ev-}u«ncG were

responsible for the deposition of this thick sequence on

the bank of Yainuna in the study area*

ihe g«mieral sequence of the bar deposits consist of

large scale trough cross bedding at lower

(IV

part foXXowed by large scal« pXaiiax cross b«iMliig again

trough cross bciilding of coi^>aratiyaXy smaller size and

of finer laateriaX follor/#d by a thin Xayer of fine

materiaX containii^ rippXe c&rift cross Xwnination in them*

Ho¥;ever» this layer is generally ercdded away or is repre­

sented by eoassive units. An over ali decrease in the

size of sediments is also observed. At the tiau^t coarse

sand with utlca flakes or organic matter is found which

passes into fin© aands silt or structureless units or

overlain by a ciud layer at the top. The huge accumulation

of the coarse sand in the foria of large scale trouqh or

planer cross bedding indicate that their development has

been taken place as a ro&ult of a high velocity current and

a rapid acci^nulation. The overlying fine sand silt and

clay ere the result of tho periodic flooding and the

strideture such as ripple drift cross lamination ere

develo|>ed because of the fluctuations in flcw v velocity

during the deposition. Th© patches oi the trough cross

bedding are the result of local infilling of the scours

and the change in the floi- ragliae conditions produces even

horizontal configuratlen of the beds*

C H A P T E R - VII

CUICLUSION

An itegrated study of seaiiDentary structures»

Xithologyt siechanical coi^posltion and the mineral ccKSposi-

tion has enables the writer to develope the fluvial models

for a alluvial meandering river systeia*

The study of the sedicaents in various trenches dug

in the bank deposits as well as in the point bar deposits

of Yasuna river shows a systematic change in grain size and

sediioentary structures from bottom to top*

Ihe sediiaents are on an average moderate to well

sorted and show general decrease in grain size from bottt^

to top* The grains are mostly angular to subrounded* The

K ineralogical study reveals that a nuiBber of rock forming

minerals are present and quartz being the dominating raises

fz(m 38 to ttlsf' by nui^ber* The other lainerals present are

kyanitop garnett tourmalinet biotitOt rauscovite* hypersthene»

hornblende» etc«» Bosm opaque minerals and rock fragments

are also present*

Flow pattern in the study area is based on the

QMiasurMwnts of cross bedding dip azi&MJths* The flow patterns

show a general direction from north to south* The distribution

of sediments is unimodal and bimodal* The frequency size

distribution shows that the sediments are very negatively

skewed to very positively skewed* The grai^ic kurtosis values

show large variations in the sediments, which are very

platykuxtic to oxtreiaely leptokurtlc.

On th« basis of th« above studios, two separate

models hswe been cieveXoped» iWxiieX-A for bank deposits

and i4odeX-B for point bar deposits*

Model-A consist of nine units starting with large

scale trough cross bedding at the base overlain by large

scale planar cross bedding which in turn is overlain by

horizontal bedding* Above the horizontal bedding small

scale trough cross bedding are present which are overlain

by ripple drift cross laiainationt convolute bedding then

wavy laniinaticm and massive units at the top* The model

show a general decrease in the scale of the ^ tuctu jfte

and grain size from bottom to top.. Model-B has been

constructed for point bar deposits which also starts with

large scale trot^h cross bedding at the base sand massive

units or ripple drift cross laminations at the top»

although s^ie intercalated patclMis of horizontal bedding

are present* This model also shovvs a decrease in the scale

of sedimentary structures and in the grain size from bott(»B

to top*

I N D E X T O T H E F I G U R E S

A - Hippie drift crod® laisination

a - Large scale planar cross bGdding

C - Sisall scale planar cross bedding

D - Large scale trough cross bedding

Sotall scalo trough cross bedding

F - Conovolute bedding

G • Horizontal bedding

H - t,vavy lamination

X - Massive unit

s c cs

»

-

-

For Lithology

Sand Clay Clay and silt

a E I E a E N c E s

Alient Jiilill.. 1963

Assyaietrical ripple marks and th«

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Allen» JiiRiL,» 1964b

Studies in f l u v i a t i l e sedicrt^ntatlon.

Six cyelotheim from the lower old red

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Sediiaentation in the Lee of small

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Allen, JmRmL*$ 1970

Physical processes of sedimentations,

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Primary atidis^ntary structuraa f02^ad

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Di@ entetehung Von

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1979 ii# Inael Mdllura (Sudliche l4ord»99)

Dynamlache F^osessa und Sedinantge-

fuga* I* Sudwatt Ubergangszone Mnd

Hochflache* Sanckenbaxgiana marlt

lit P* 59-Xi3#