report on shale

8/10/2019 Report on shale

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CHAPTER-1

INTRODUCTION

1.1 Krishna-Godavari Basin

The Krishna-Godavari basin extends approximately from Nellore in the south to Kakinada in

the north and it includes the two large east coast rivers viz Krishna and Godavari It is one of

the promising petroliferous basins of India. The basin has a half-crescent shape and measures

about 15,000 km z on land and about 25,000 km 2 of the adjoining offshore regions (Kumar,

1983). It is a pericratonic basin as it occurs on the margin of the Indian craton formed of

highly metamorphosed pre-Cambrian rocks. The maximum sediment thickness of the onshore

basin is of the order of 6000 m while in the offshore it reaches as much as 8000 m (Prabhakar

and Zutshi, 1993). Based on geophysical surveys carried out by the Oil and Natural Gas

Commission (ONGC), India, the onshore basin (Fig. 4) is divided into three sub-basins viz

the Krishna, the West and East Godavari sub-basins, by the two prominent NE-SW basement

ridges called the Bapatla and Tanuku Horsts (Mohinuddin et al., 1993). The West Godavari

subbasin is further subdivided into two parts by the Kaza ridge. Three major NW-SE

basement faults namely, the Avanigadda Cross Trend (ACT), Chintalapudi Cross Trend

(CCT) and the Pithapuram Cross Trend (PCT) were identified by ONGC from seismic data of

the onshore basin (Rao, 1993; Mohinuddin et al., 1993). Two of these trends namely the ACT

and the CCT are shown in Fig. 4, while the PCT further northeast is located outside the study

area. The NW-SE Pranhita-Godavari Gondwana graben of early Cretaceous age is located

between Chintalapudi and Pithapuram cross trends and seismic data of ONGC (Mohinuddin

et al., 1993) suggest its extension below the east Godavari sub-basin (Fig.4) though its

offshore extension is not clearly established.


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Stratigraphy of KG Basin

1.2Komatigunta

Komatigunta is situated in Gopalapuram tehsil and located in West Godavari district of Andhra

pradesh.The latitude 1655'22.78"N and longitude 8124'3.51"E.

1.3Dwarakatirumala

Dwarakatirumala is a village and amandal inWest Godavari district in the state ofAndhra

Pradesh inIndia.It located in 1653'2.03"N and 8115'18.29"E latitude and longitudes respectively.

Post Raghavapuram Shale tilt of the basin was best demonstrated by the increased thickness

of Upper Cretaceous sediments in SW/SE directions. The tilt might be due to relative basin

ward subsidence of crustal blocks. This tilt was followed by major marine conditions and was

responsible for the significant thickness of Upper Cretaceous section in SW and SE

directions. Outcrop of this unit are present near Dwaraka-Tirumala town in West Godavari

district. Lithologically, the lower section is argillaceous and is characterized by low gamma-

low resistivity. The upper part is arenaceous consisting predominantly sands- hard, dark

brown, medium to coarse grained and ferruginous. Based on the palynofloral assemblages,
http://en.wikipedia.org/wiki/Subdivisions_of_Indiahttp://en.wikipedia.org/wiki/West_Godavari_districthttp://en.wikipedia.org/wiki/Andhra_Pradeshhttp://en.wikipedia.org/wiki/Andhra_Pradeshhttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Andhra_Pradeshhttp://en.wikipedia.org/wiki/Andhra_Pradeshhttp://en.wikipedia.org/wiki/West_Godavari_districthttp://en.wikipedia.org/wiki/Subdivisions_of_India


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Upper Cretaceous age (Campanian to Early Maastrichtian) has been assigned to this

Formation. While transitional to marginal marine depositional conditions have been inferred

for this Formation, the thick sequence of coarse grained sandstone is inferred due to a

regressive phase.

1.4Raghavapuram Shale: The Raghavapuram Shale was deposited in West Godavari

sub basin and Mandapeta-Endamuru area delimited in the south by MTP fault. It is evidenced

by the onlapping seismic reflections of this sequence onto the sequence corresponding to the

rift fill on either side of each of these areas. This sequence wedges out towards SW in

Gudivada Graben, over Kaikalur Horst and Bantumilli Graben and in SE against Poduru-

Yanam. Wedging out of this sequence towards SW and SE suggests probable slope towards

NE/NW. Both top and bottom of this unit are unconformities. In the wells drilled on the

northwestern flanks of highs, the lower one is an angularunconformity with the underlying

Gollapalli/ Kanukollu Formations showing a dip of 25- 30 degrees NW and the upper one

with Tirupati Sandstone having a dip of 2 degrees SE.

The Raghavpuram shales a middle division of the upper gondwanas of the east coast and of lower

cretaceous age have yielded a very rich assemblage of arenaceous foraminifera consisting of 15

species where as the homo taxial beds of the vammevaram area as well as the marine equivalence of

the tirupati sandstones yet ayaparaz kotapilli, are devoide of micro fauna.the foraminifera of the

raghavapuram shales at the type sections are quiet rich in number of specimens but not in number of

species and genera.


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1.5Loction map


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REFERENCE POSITION AT SAMPLE S4


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OBJECTIVES

To identify and differentiate variours samples of Raghavapuram shale in different

locations.

Characterisation of Raghavapuram shales in different locations by textural, organic

matter studies.


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CHAPTER-2

TEXTURAL STUDIES

2.1Introduction

Texture is a distinguishing feature of sediment. It is the result of the forces acting on

the sediment at the time of and after their deposition. Textural characteristics of riverine

sediments depend on the source area, morphology of the river basin and hydrodynamics of

the fluvial system, whereas characteristics of the estuarine sediments are controlled by

circulation pattern of the estuarine which, in turn, is influenced by the fluvio-marine process.

Normally, the influence of the seasonal hydrodynamic conditions would reflect in the textural

variations of sediments. In marine environment, grain size characteristics of sediments are the

result of the forces acting on them at the time of and subsequent to their deposition. Once the

sediment reaches the site of deposition under marine conditions its characteristics are

influenced by number of factors including the configuration of shoreline, waves, currents, sea

level oscillations and bottom relief. Thus the study of grain size characteristics assumes

importance in deciphering pre and post depositional history of sediments. Grain size

parameters are used as indicators of depostitonal environments (Udden 1914, Wentworth,

1929, Krumbein and Pettijohn, 1938, Folk and Ward, 1957, Friedman, 1979, Passega, 1957,

1964).

Any sedimentary environment is a product of unique set of physical, chemical and

biological conditions in a geomorophic unit (Reineck and Singh, 1980). Statistical treatment

of the data on grain size measurements evidently brings out the discrimination present among

the environments. There have only bee n a few attempts so far to characterize modern deltaic


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environments of india(Rao and Swamy, 1995, Gandhi, et. al., 2000), and they were restricted

to only some of the many sub-environments of the deltaic systems

2.2 Method of Study

Sieve Analysis:

About 150 to 200 grams of each sample is taken in porcelain dish and air dried, taking

all possible care against contamination. In the laboratory, the bulk sample in each case was

reduced by coning and quartering and representative samples of nearly 50 grams weight were

taken for granulometric studies. All the samples were treated with dilute HCL and distilled

water to remove shell fragments and salts. They were then oven dried. The dried samples

were later sieved on a Ro-tap sieve shaker for 15 minutes using ASTM test sieves of 8

diameter with successive sieves spaced at 1/2 phi intervals. Material, thus retained on each

sieve is weighed.

2.3 Particle size analysis:

For determining the silt and clay percentages of the samples the instrument Particle

size analyzer (Malvern Mastersizer 2000/2000E, UK) was used and next the following

methodology was adapted. First 50 grams of each sample are taken in porcelain dishes and air

dried, taking all possible care against contamination.

Samples were repeatedly washed in distilled water for removal of salts and then dried. H 2O2

and Hcl were added to remove organic matter and shell material in the sample and then dried.

Wet sieving is done normally to separate in to mud (-63 m), sand (+63 m to 2000 m) and

gravel fraction (>2 mm). However, in the Laser Particle size analyzer only the gravel portion


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is required to be separated out by sieving because the instrument can analyze grains in the

range of 0.01 m to 2000 m.

Before added the sample (-63 m), the instrument is cleaning is necessary ( three times using

distilled water 700 ml in 1000ml beaker and sample analysis using de-ionised water 0.22

m). Di-Sodium Oxalate is added 0.04 g for the dispersion of the sediment sample then

around 0.5 ml of sediment sample were added upto obscuration range, and run the instrument

for the further analysis. The instrument gives the particle size in terms of volume percentages

in the sizes namely 44 m, 31 m, 23.5 m, 15.5 m, 7.7 m, 3.8 m, 1.9 m and 0.1 m.

These values are converted to weight percentage and finally the individual percentages were

obtained using standard methodology (Folk and Ward, 1957) & also G-Stat software was

used for Grain size statistical analysis, sediment classification, graphic measures, etc.

designed and developed by A.C. Dinesh, Geologist, Geological Survey of India, Mangalore.

A triangular diagram (Shepard, 1954) was used to represent the sand, silt and clay rations of

the sediments. CM diagram (Passega, 1957) was drawn using the data of first percentile (C)

and median (M) of the grain size distributions.

2.4 RESULTS AND DISCUSSION

Table.1. Textural classification and Grain size parameters of sediments from different

sub environments of Komatigunta , dwaraka tirumala ,raghavapuram .

SampleNo. Median Mean SD Skewness Kurtosis remarks

K1 5.078 5.334 1.707 0.227 0.803 S,PS,NS,PK

K2 5.685 5.729 1.449 0.049 0.918 S,PS,NS,MK

K3 5.751 5.857 1.433 0.101 0.911 S,PS,PSK,MK

K5 4.933 5.156 1.636 0.216 0.897 S,PS,PSK,PK

K6 4.715 4.928 1.656 0.208 0.865 S,PS,PSK,PK

K7 5.043 5.143 1.643 0.106 0.882 S,PS,PSK,PK

K8 5.123 5.251 1.492 0.146 0.925 S,PS,PSK,MK


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K9 6.393 6.292 1.596 -0.1 0.86 S,PS,NS,PK

K10 5.272 5.428 1.655 0.153 0.822 S,PS,PSK,PK

K11 5.775 5.775 1.675 0.006 0.787 S,PS,NS,PK

K12 4.422 4.705 1.625 0.278 0.88 S,PS,PSK,PK

K13 6.889 6.778 1.433 -0.137 0.911 S,PS,NSK,MK

K14 5.429 5.494 1.399 0.08 0.975 S,PS,NS,MK

K15 5.984 5.909 1.779 -0.052 0.816 S,PS,NS,PK

K16 3.872 4.287 1.765 0.349 0.958 S,PS,VPSK,MK

K17 6.355 6.406 1.412 0.028 0.892 S,PS,NS,PK

K18 6.501 6.391 1.81 -0.055 0.788 S,PS,NS,PK

K19 6.761 6.705 1.384 -0.087 0.919 S,PS,NS,MK

K20 5.626 5.704 1.496 0.084 0.907 S,PS,NS,MK

K21 6.442 6.418 1.484 -0.052 0.893 S,PS,NS,PK

K22 4.715 4.974 1.554 0.273 0.97 S,PS,PSK,MK

K24 5.13 5.259 1.687 0.114 0.849 S,PS,PSK,PKK25 6.025 5.959 1.632 -0.06 0.851 S,PS,NS,PK

K26 4.891 5.142 1.728 0.213 0.875 S,PS,PSK,PK

K27 4.815 5.011 1.58 0.211 0.93 S,PS,PSK,MK

K28 5.814 6.115 1.724 0.237 0.847 S,PS,PSK,PK

S1 6.341 6.448 1.376 0.102 0.847 S,PS,PSK,PK

S2 5.939 6.124 1.374 0.192 0.886 S,PS,PSK,PK

S3 6.189 6.33 1.309 0.152 0.886 S,PS,PSK,PK

S4 6.421 6.393 1.384 -0.041 0.861 S,PS,NS,PK

S6 6.598 6.572 1.416 -0.036 0.838 S,PS,NS,PK

S7 6.855 6.83 1.258 -0.037 0.871 S,PS,NS,PK

S8 5.855 5.958 1.528 0.094 0.837 S,PS,NS,PK

S9 7.156 7.083 1.148 -0.12 0.947 S,PS,NSK,MK

S10 7.042 6.991 1.248 -0.067 0.873 S,PS,NS,PK

S11 7.07 7.024 1.181 -0.071 0.904 S,PS,NS,MK

s12 7.08 7.046 1.193 -0.055 0.915 S,PS,NS,MK

S13 6.296 6.377 1.358 0.078 0.873 S,PS,NS,PK

S14 6.924 6.882 1.259 -0.059 0.878 S,PS,NS,PK

S15 6.494 6.528 1.487 0.019 0.867 S,PS,NS,PK

S16 6.921 6.904 1.256 -0.039 0.878 S,PS,NS,PKR1 7.382 7.307 1.237 -0.085 0.943 S,PS,NS,MK

R2 6.678 6.656 1.398 -0.034 0.846 S,PS,NS,PK

R3 6.993 6.9 1.364 -0.115 0.902 S,PS,NSK,MK

R5 6.948 6.893 1.198 -0.08 0.89 S,PS,NS,PK

R6 6.723 6.633 1.495 -0.096 0.842 S,PS,NS,PK

R7 6.397 6.376 1.462 -0.047 0.89 S,PS,NS,PK

MS-Medium sand, CS- Corse Sand, FS- Fine Sand, MWSd- Moderately well sorted, MSd-

Moderately Sorted, WS- Well Sorted, SySk- Symmetrically skewed, CSk- Coarse Skewed,


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VCSk- Very Coarse Skewed, Lk- Leptokurtic, FSk- Fine Skewed, Pk- Platykurtic, Mk-

Mesokurtic, Lk- Leptokurtic .

Table.2. Range and average values of grain size parameters of Komatigunta, dwaraka

tirumala, raghavapuram sediments of environments.

Place Name Range Mean SD Kurtosis Skewness

Min 4.287 1.384 0.787 -0.137

Kommatigunta Max 6.778 1.81 0.975 0.349

Avg 5.5325 1.597 0.881 0.106

Min 5.958 1.148 0.837 -0.071

DwarakaTirumala Max 7.083 1.487 0.947 0.192

Avg 6.5205 1.3175 0.892 0.065

Min 6.376 1.198 0.842 -0.115

Raghavapuram Max 7.307 1.495 0.943 -0.034

Avg 6.8415 1.3465 0.8925 -0.0745

Kommatigunta

The Kommatigunta sediments are silt with mean size ranging from 4.287 to 6.778 (av. 5.5325); and

they are poorly sorted with standard deviation ranging from 1.384 to 1.81 (av. 1.597); negitively

skewed to very positively skewed with skewness varying from0.137 to 0.349 (av. 0.106) and shows

platykurtic to Mesokurtic nature with kurtosis varying from 0.787 to 0.975 (av. 0.881).


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Dwaraka Tirumala

The Dwaraka Tirumala sediments are silt with mean size ranging from 5.958 to 7.083 (av. 6.5205);

and they are poorly sorted with standard deviation ranging from 1.148 to 1.487 (av. 1.3175); near

symmetrical with skewness varying from 0.071 to 0.192(av. 0.065) and shows platykurtic to

Mesokurtic nature with kurtosis varying from 0.837 to 0.947 (av. 0.892).

Raghava Puram

The Raghavapuram sediments are silt with mean size ranging from 6.376 to 7.307 (av. 6.8415); and

they are poorly sorted with standard deviation ranging from 1.198 to 1.495(av. 1.3465); near

symmetrical with skewness varying from 0.115 to - 0.034(av. -0.0745) and shows platykurtic to

Mesokurtic nature with kurtosis varying from 0.842 to 0.943 (av.0.8925).

Mean size

The graphic mean size is the average size of the sediments represented by mean size

and mainly is an index of energy conditions.

The variation in mean size is a reflection of the changes in energy condition of the

depositing media and indicates average kinetic energy of the depositing agent (Sahu, 1964).

But there is no predominant variation in mean size for Komatigunta , Raghavapuram ,

Dwarkatirumala Samples.

Standard deviation

The graphic Standard deviation indicates the difference in kinetic energy associated

with mode of deposition or uniformity of particle size distribution. It is an important

parameter in sediment analysis because it reflects the energy conditions of depositional

environment but it does not necessarily measure the degree to which the sediment has been

mixed (Spencer, 1963).


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Skewness

The graphic Skewness measures the symmetrical distribution, i.e. predominance of

coarse or fine-sediments. The negative value denotes coarser material in coarser-tail i.e.,

coarse skewed, whereas, the positive value represents more fine material in the fine tail i.e.,

fine-skewed.

Kurtosis

The graphic kurtosis is a quantitative measure used to describe the departure from

normality of distribution. It is a ratio between the sorting in tails and central portion of the

curve. If the tails are better sorted than the central portion, then it is termed as

leptokurtic, whereas, it is platykurtic in opposite case, or mesokurtic if sorting is uniform

both in tails and central portion.

2.5 Frequency Distribution Curves of different locations.

Frequency distribution curves are used to describe the modality of the sediments. The mode

is the centre of the size class that contains most of the sediment, either in terms of weight

frequency or number frequency. An analysis of modality determines the number of modes in

a distribution. Distribution can be unimodal (one mode), bimodal (two modes), or polymodel

(several modes). A sample having one particular size of sediments dominating over other will

be called unimodal and will be represented on the size frequency curve by more or less

conspicuous peak. Curves with two prominent peaks will be termed by model. Curves with

three or more prominent peaks will be termed poly modal.

Bimodality can indicate the presence of two distinct particle size populations,

supplied from a different source, it perhaps different petrology and abrasion resistance, and

each population may have had a different transport distance. The recognition and


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characterization of the degree bimodality is important for studies of sedimentation and fluvial

geomorphology because incipient motion conditions and transport behaviour are different in

unimodal and bimodal sediment mixtures (Wilcock, 1993).

The frequency distribution curves (FDC) are used to describe the nature of

sediments and exhibit the pictorial representation of weight percentage of different

fractions of sediments.

Komatigunta frequency distribution curves

Unimodal graphs

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k19

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K21


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2.6 Bi-modal graphs

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2.7 Poly modal graphs

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Weight%

Mean Size

k 14


23/48

23

2.8 Komatigunta

0

5

10

15

20

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

W

eight%

Mean Size

K16

-5

0

5

10

15

20

25

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

Weight%

Mean Size

K20

0

5

10

15

20

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

k28


24/48

24

The sediments from komatigunta sample having high amount of silt , less amounts of very

fine sands and clay . But sample No.K26 & K 16 show small amounts coarse sand (0.63 ).

Total sediments in the komatigunta are of bimodal nature with silt. The sediment here are

supplied from more than one source.

2.9 Dwaraka Tirumala frequency distribution curves

0

5

10

15

20

25

30

weight%

mean size

k1

k2

k3

k5

k6

k7

k8

k9

k10

k11

k12

k13

k14

k15

k16

k17

k18

k19

k20

k21

k22

k24

k25

k26

k27

k28


25/48

25

Uni modal graphs

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S1

0

5

10

15

20

25

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S2

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S3


26/48

26

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight

%

mean

S4

0

5

10

15

20

25

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S6

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S7


27/48

27

0

5

10

15

20

25

30

35

40

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight

%

mean

S9

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S10

0

5

10

15

20

25

30

35

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S11


28/48

28

0

5

10

15

20

25

30

35

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight

%

mean

S12

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S13

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S14


29/48

29

0

5

10

15

20

25

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight

5

mean

S15

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

S16


30/48

30

Dwaraka Tirumala

The sediments from sample S8,S15 show small amounts of very fine sand (1.97-2.73 ).

Remaining sediments in the Dwaraka Tirumala are of Unimodal nature with silt. The

sediment here are supplied from one source.

0

5

10

15

20

25

30

35

40

Weight%

Mean

s1

s2

s3

S4

S6

S7

S8

S9

S10

S11

S12

S13

S14

S15

S16


31/48

31

Raghavpuram

Uni modal graphs

0

5

10

15

20

25

30

35

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

R1

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

R2

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

R3


32/48

32

0

5

10

15

20

25

30

35

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight

%

mean

R5

0

5

10

15

20

25

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

R6

0

5

10

15

20

25

30

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

weight%

mean

R7


33/48

33

Raghavapuram

sediments in the Raghavapuram are of Unimodal nature with silt. The sediment here are

supplied from one source.

2.10 CM Diagrams

Passega (1964, 1977); Visher (1969), Kumar and Singh (1978) and several other

workers have used the grain size parameters and the plots of CM patterns to distinguish

between the sediments of different environments. The parameters C (one percentile of the

grain size distribution) and M (the median) were plotted for phi values of the C and M

obtained from the cumulative curves in microns. The relation between C and M is the effect

of sorting by bottom turbulence. The good correlation between C determined by only one

percent by weight of the sample and M, which represents grain size as a whole, shows the

precision of the control of sedimentation by bottom turbulence.

The CM pattern is sub divided into segments namely PQ, QR and RS (passega, 1977).

Segment PQ indicates the coarse grains transported by rolling, while QR parallel to line C=M

represents the main channel deposits. RS parallel to the M axis indicates the uniform

suspension. Points of (1) in the represent deposition from Rolling. Points of (2) represent

0

5

10

15

20

25

30

35

0

0.

41 1

1.

4 2

2.

41 3

3.

4

3.

988

4.

5

5.

01

5.

41

6.

01

7.

02 8 9

13

.28

Weight%

Mean

R1

R2

R3

R5

R6

R7


34/48

34

deposition from bottom suspension & rolling. Points of (3) represent deposition from graded

suspension no rolling. Points of (4) represent deposition from uniform suspension. Points of

(5) represent deposition from pelagic suspension. In the present study an attempt has been

made to identify the modes of deposition of core sediments by CM patterns.

Basic CM diagram represents tractive current and pelagic .Most of samples have fallen under

pelagic suspension of those 4 samples of komatigunta fallen under pelagic. Raghavapuram and

Dwaraka tirumala samples are formed under pelagic.


35/48

35

K12, K6, K24, K5, K27, K22, K8, K1, K10, K14, K20, K11, K15 , K25 are deposited

uniformly during flooding.

K16,k26 are having graded suspension and no rolling(from coarse to fine grading)

K3, K28, S8, K9, S15, R7, R6, K13, S4, S2, S3, S1, R2, R3, S7, S14, S10, S12, S9,R1 are

very fine sediments having pelagic suspension formed at low energy environment like lagoon.


36/48

36

2.11 Scatter Plots

Scatter plots between certain parameters are also helpful to interpret the energy conditions,

medium of transportation, mode of deposition etc. Passega (1957), Visher(1969), Folk

and Ward (1957) and others described that these trends and interrelationship exhibited in the

scatter plots might indicate the mode of deposition and in turn aid in identifying the

Environments. Scatter plots are useful for understanding the geological significance of the

grain size parameters. Inman (1949) and Griffiths (1951) are the earliest workers to notice in

their experiments, the physical relationship between median diameter, standard deviation

and skewness measures. Folk and Ward (1957), Mason and Folk (1958),Friedman (1961,

1967), Moiola and Weiser (1968) have used the values of graphic mean, inclusive graphic

standard deviation, graphic skewness and graphic kurtosis etc., to demarcate the fields of

komatigunta , Raghavaghavapuram, Dwaraka tirumala. Scatter plots viz. mean size vs.

Standard deviation, mean vs. Skewness and standard deviation vs. skewness were drawn to

understand the relationship between different size parameters.

Mean Size Vs standard deviati on

0

0.2

0.4

0.6

0.8

1

1.21.4

1.6

1.8

5.5 6 6.5 7 7.5

standarddeviation

Mean

mean Vs sd

dwaraka tirumala

Linear (dwaraka

tirumala)


37/48

37

All the samples collected from 3 areas i.e Komatigunta, Raghavapuram, Dwaraka tirumala

are having a mean size of 4-9 . The nature of the sediments is dominantly unimodal, of

which, the dominant constituent is silt. As the standard deviation ranges from 1-2 the

sediments are poorly sorted.

0

0.2

0.4

0.6

0.8

1

1.2

1.41.6

1.8

2

0 2 4 6 8

standarddeviation

mean

mean Vs sd

komatigunta

Linear (komatigunta)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

6 6.5 7 7.5

stan

darddeviation

mean

mean Vs sd

Raghavapuram

Linear (Raghavapuram)


38/48

38

Mean Size Vs Skewness

The bivariate plot between Mean size and Skewness (Fig.7b) clearly brings out the values, which fall

in the range of Negatively skewed to very positively skewed , with a mean size range of 4.287 to

6.7 . It further indicates a unimodal nature of sediments with higher percentage of silt.

The bivariate plot between Mean size and Skewness (Fig.7c) clearly brings out the values, which fall

in the range of Negatively skewed to possitively skewed, with a mean size range of 5.958 to 7.083

. It further indicates a unimodal nature of sediments with higher percentage of silt.

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

5.5 6 6.5 7 7.5

skewnes

Mean size

Ms Vs. Sk

Dwaraka tirumala

Linear (Dwaraka

tirumala)

-0.2

0

0.2

0.4

0 2 4 6 8

Skewnes

Mean Size

Mz Vs. Sk

komatigunta



39/48

39

The bivariate plot between Mean size and Skewness (Fig.7d) clearly brings out the values, which fall

in the range of Near symmetrical to very negatively skewed, with a mean size range of 6.376 to

7.307 . It further indicates a unimodal nature of sediments with higher percentage of silt.

Mean Vs Kur tosis

The relation between Mean size and Kurtosis (Fig.8a) values indicates a dominance of platykurtic

(0.67 F to 0.90 F) category followed by mesokurtic (0.90 F to 1.11F), in the size class range of 4.287

to 6.778 i.e. silt.

-0.14

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

6 6.5 7 7.5

AxisTitle

Axis Title

Ms Vs. Sk

Raghavapuram


0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8

kurtosis

mean

mean Vs Kurtosis

komatigunta



40/48

40

The relation between Mean size and Kurtosis values indicates a dominance of platykurtic (0.67 F to

0.90 F) category followed by mesokurtic (0.90 F to 1.11F), in the size class range of 5.958 to 7.083

i.e. silt.

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

5.5 6 6.5 7 7.5

kurtosis

mean

mean Vs kurtosis

dwarakatirumala

Linear

(dwarakatirumala)

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

6 6.5 7 7.5

Kurtosis

Mean size

mean Vs kurtosis

RaghavaPuram

Linear (RaghavaPuram)


41/48

41

The relation between Mean size and Kurtosis (Fig.8a) values indicates a dominance of

platykurtic (0.67 F to 0.90 F) category followed by mesokurtic (0.90 F to 1.11F), in the size

class range of 4.287 to 6.778 i.e. silt.


0.90 F) category followed by mesokurtic (0.90 F to 1.11F), in the size class range of 5.958 to 7.083

i.e. silt.

0.82

0.84

0.860.88

0.9

0.92

0.94

0.96

5.5 6 6.5 7 7.5

kurtosis

mean

mean Vs kurtosis

dwarakatirumala

Linear

(dwarakatirumala)

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

6 6.5 7 7.5

Kurtosis

Mean size

mean Vs kurtosis

RaghavaPuram

Linear (RaghavaPuram)


42/48

42


0.90 F) category followed by mesokurtic (0.90 F to 1.11F), in the size class range of 6.37 to 7.307 i.e.

silt.

CHAPTER-3

GEOCHEMISTRY

3.1 INTRODUCTION

Several factors control the accumulation of organic matter in modern sediments i.e.

rate of supply of organic matter to the depositional environment and/or rate of preservation

(Muller and Suess, 1979; Demaison and Moore, 1980; Arthur et al, 1984; Tissot and Welte,

1978). Settling of organic matter is highest in areas where deposition of fine grained

sediment takes place.

The organic carbon (OC) is often a good index for deciphering depositional

environment. Its plays a major role in controlling the redox potential of the sediment of

source material for petroleum. The amount of organic carbon in marine sediments reflects

the supply and preservation of organic materials from marine and terrestrial sources (Tissot

et al. 1980, Summerhayes, 1981).

Accumulation of organic carbon in the sediments in general, depends on production

and deposition rate (this includes also decomposition and consumption of organic carbon

after deposition), the rate of burial and dilution by clastics, sediment characteristics and

texture.

The variation in carbonate content in the bulk sediments is mainly due to the shell

fragments and tests of organisms, inorganic and organic precipitation, and the supply of

carbonate minerals by the rivers. However, the estuarine environment showed a high


43/48

43

amount of carbonate content consequent on the abundance of shell fragments of molluscas

and other shells with a number of zooplankton tests.

3.2 METHOD OF STUDY

Organic carbon, calcium and magnesium carbonate content were estimated in all

selected sub-samples and examined its distribution in the core sediments.

3.3 `Organic Carbon

Organic carbon is one of the most important content in the sediments (Sverdrup et

al., 1942; Trask, 1939). This organic carbon is determined by the process of titration

between potassium dichromate and ferrous ammonium sulphate. This process is also called

Walkey-Blacks method (Jackson, 1967; Gaudette et al., 1974).

For the estimation of organic carbon, 0.5 gm of powdered sample is taken into a 500 ml

conical flask. To this, 10 ml of a 1N potassium dichromate is added. 20 ml of concentrated

H2SO4is added to the above solution and kept inside the solution for about 20-30 minutes.

Then 170 ml of distilled water is added to the solution, along with this 10 ml of phosphoric

acid, 0.2 gm of sodium fluoride and 30 drops of di-phenyl amine indicator are added. The

solution is titrated against 0.5N ferrous ammonium sulphate which is taken in burette. The

end point of the titration is brilliant green. This process is also carried out with blank, to

estimate error.

Percentage of Total Organic Carbon= (1-T/S)x10

Where S= Blank Titration

T= Sample Titration

Percentage of Organic Matter= 1.724(1-T/S)x10


44/48

44

1.724 is Marine Water

1.34 is Fresh Water

Table.1. TOTAL ORGANIC CARBON (TOC)

Core Sample no. Titration value in

mille liters

Mean size

()TOC

%

Total organic

matter %

R1 18.9 7.307 0 0

R4 18.7 6.9 0.105 0.1824

R6 18.9 6.633 0 0

S2 18.2 6.124 0.37 0.638

S5 18.8 6.598 0.052 0.089

S15 18.7 6.528 0.105 0.182

K11 13.2 5.775 2.788 4.804

K8 10.3 5.251 4.371 7.536

K19 11.3 6.705 3.825 6.594

K16 14.3 4.287 2.185 3.768

K15 12.4 5.909 3.224 5.558

K12 11.4 4.705 3.770 6.500

K20 10.4 5.704 4.316 7.440


45/48

45

K7 13.8 5.143 2.459 4.239

K22 12.4 4.974 3.224 5.558

K17 11.7 6.406 3.606 6.217

K21 10.9 6.418 4.043 6.971

sample wise description:The percentage of mean size, organic carbon of raghavapuram core

sediment samples are presented in Table. 3.2 and percentage of organic carbon, and mean

size () variations are shown in Fig.3.5.

Organic Carbon: The organic carbon contents in Raghavapuram core varied from 0 % to

0.105 % with an average of 0.035%. The organic carbon content in Raghavapuram core

from surface to bottom is observed increasing trend.

Dwaraka tirumala: (S)

sample wise description:The percentage of mean size, organic carbon ofDwaraka tirumala

0

0.02

0.04

0.06

0.08

0.1

0.12

6.4 6.6 6.8 7 7.2 7.4

%organiccarbon

Mean

Raghavapuram

Raghavapuram



46/48

46

core sediment samples are presented in Table. 3.2 and percentage of organic carbon, and

mean size () variations are shown in Fig.3.5.

Organic Carbon: The organic carbon contents in Dwaraka tirumalacore varied from 0.052

% to 0.37 % with an average of 0.175%. The organic carbon content in Raghavapuram core

from surface to bottom is observed decreasing trend.

Komatigunta : (K)

Core wise description:The percentage of mean size, organic carbon ofDwaraka tirumala

core sediment samples are presented in Table. 3.2 and percentage of organic carbon, and

mean size () variations are shown in Fig.3.5.

Organic Carbon: The organic carbon contents in Dwaraka tirumalacore varied from 2.185

% to 4.371 % with an average of 3.437%. The organic carbon content in Raghavapuram

core from surface to bottom is observed decreasing trend.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

6 6.2 6.4 6.6 6.8

%organiccarbon

Mean

dwaraka tirumala

dwaraka tirumala

Linear (dwaraka

tirumala)


47/48

47

Table 2: The Range and average values of mean size ()and organic carbon % of all samples.

Core details Range Mean Size () Organic Carbon (%)

Komatigunta

Max 6.705 4.371

Min 4.287 2.185

Avg 5.570 3.437

Raghavapuram

Max 7.307 0.105

Min 6.633 0

Avg 6.946 0.035

Dwaraka tirumala

Max 6.598 0.175

Min 6.124 0.37

Avg 6.416 0.175

0

1

2

3

4

5

0 2 4 6 8

%organiccarbon

Mean size

komatigunta

komatigunta



48/48

REFERENCES

Dr. T. Karunakarudu, M.sc. (tech), Textural and heavy mineral characteristics of different

sub-environments of Mahanadi Delta, East coast of India

D. Rajasekhara Reddy, T. Karuna Karudu & D. Devavarma, Textural Characteristics of

Southwestern Part of Mahanadi Delta, East Coast of India

Passega, R. 1964. Grain size representation by CM patterns as a geological tool. Jour. Sed.

Petrol

Passega, R. 1977. Significance of CM diagrams of sediments deposited by suspensions.

Sedimentology..

Reineck, H.E. and Singh, I.B. 1973. Depositional Sedimentary environments. Springer-

Verlag, New York

report on shale

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