SEDIMENTOLOGY OF THE GODAVARI DELTA AROUND RAZOLE, EAST QODAVARI DISTRICT, ANDHRA PRADESH
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A DISSERTATION StAmttted in partial fidfiUnaU of the requirementM for the award tf the degree of 0iUSittt of $I|tlO£!op()P IN GEOLOGY ^
BY TADALA RAMABRAHMAM
DEPARTMENT OF GEOLOGY FACULTY OF SCIENCE ALIGARH MUSUM UNIVERSITY ALIGARH (INDIA) 1994 BS2600
7 Dated 2^ /^- fU Ref. No.- /Geol. CERTIFICATE PROFESSOR B.D. BHARDHAJ I certify that the. work presented in this dissertation has been carried out by Mr. Tadala Ramabrahmam, under my supervision. The work is an original one and has not been submitted for any other degree at this or any other University. (B.D. Bhardwaj) TO MY LOVING SISTER & BROTHER-IN-LAW ACKNOWLEDGEMENTS I wish to express my deep sense of gratitude to my supervisor Prof. B.D. Bhardwaj for his support, guidance, constructive criticism and encouragement throughout the course of this study. I wish to thank Prof. Iqbaluddin, Chairman Department of Geology, A.M.U. Aligarh and Director, Remote Sensing Application Centre for resource evaluation and geo- engineering, A.M.U., Aligarh for providing necessary facilities during the course of this research work. I am thankful to Dr. Adal Singh, Mr. Md. Erf an Ali Mondal, Mr. Mohd. Asif and to Dr. A.H.M.Ahmad for all the help and cooperation I received from them during the course of this study. A token of deep appreciation to B.T. Ashok and Syed Jalal Khundmiri for the guidance and kind help all through the course of my study as well as in the compilation of this dissertation. I acknowledge the help and cooperation received from Mr. Adil Anwar, Mr. S.A. Rashid, Mr. Asad Umar, Mr. Haris Umar, Mr. Arif Khan and Mr. Uma Shankar. I wish to express my heartfelt gratitude to Mrs. and Mr. Kodi Venkateswara Rao, Mr. Adinarayana who have always supported me in all my academic endeavours and showered their love on me. Thanks are also due to Messrs Z.Husain, Salimuddin and A. Ali, Department of Geology A.M.U., Aligarh for library facilities, painstaking cartographic designs and prepartion of thin sections, respectively. (TADALA RAMABRAHMAM) 111 CONTENTS Page No. CERTIFICATE 11 ACKNOWLEDGEMENTS 111 LIST OF FIGURES VI LIST OF TABLES XI LIST OF PLATES Xll CHAPTER - I INTRODUCTION 1 Location and Environs of the area 2 Godavari River 2 Geomorphological Setting 4 Methods of Investigation 4 Field Method 4 Laboratory Method 5 CHAPER - II FACIES DESCRIPTION 7 Trough Cross Bedded Sandy Facies (St) 9 Planar Cross Bedded Sandy Facies (Sp) 11 Horizontal Bedded Sandy Facies (Sh) 13 Ripple Cross Laminated Sandy Facies (Sr) 15 Parallel Laminated Fine Sandy Facies (Fl) 18 Lenticular Sandy Facies (Si) 18 Massive Silt and Mud Facies (Fm) 20 IV CHAPTER - III DISTRIBUTION OF GRAIN SIZE IN RELATION TO SEDIMENTARY STRUCTURE 22 General 22 Ripple Cross Laminated Sandy Facies (Sr) 27 Planar Cross Bedded Sandy Facies (Sp) 40 Trough Cross Bedded Sandy Facies (St) 43 Horizontal Bedded Sandy Facies (Sh) 44 Lenticular Sandy Facies (SI) 45 Parallel Laminated Fine Sandy Facies (Fl) 46 Massive Silt And Clay Facies (Fm) 46 Vertical Variation in Grain Size 49 CHAPTER - IV MINERAL COMPOSITION OF GODAVARI SEDIMENTS 52 CHAPTER - V FLOW PATTERNS 62 Vector Mean 63 Vector Strength 63 Variance 66 Interpretation 66 CHAPTER - VI DELTA MODEL 68 CHAPTER - VII CONCLUSION 73 REFERENCE 76 LIST OF FIGURES Page No Fig. - 1 Map of the study area and location of trenches. 3 Fig. - 2 Log probability plots of grain size distribution in Trench No.l. 29 Fig. - 3 Log probability plots of grain size distribution in Trench No. 2. 30 Fig. - 4 Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 1. 31 Fig. - 5 Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 2. 31 Fig.- 6 Log Probability plots of grain size distribution in Trench No. 5. 32 Fig.- 7 Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 5. 33 VI Fig.- 8 Log probability plots of grain size distribution in Trench No. 9. 34 Fig.- 9 Log probability plots of grain size distribution in Trench No. 10. 35 Fig.-10 Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 9. 36 Fig.-11 Vertical variation in facies in relation to Mean size, S.deviation, Skewness and Kurtosis in Trench No. 10. 36 Fig.-12 Log probability plots of grain size distribution in Trench No. 3. 37 Fig.-13 Log probability plots of grain size distribution in Trench No. 4. 38 Fig.-14 Vertical variation in facies in relation to Mean size, S.deviation, Skewness and Kurtosis in Trench No. 3. 39 Fig.-15 Vertical variation in facies in relation to Mean size, S.deviation, Vll Skewness and Kurtosis in Trench No. 4. 39 Fig.-15 Log probability plots of grain size distribution in Trench No. 6. 41 Fig.-17 Vertical variation in facies in relation to Mean size, S.deviation, Skewness and Kurtosis in Trench No. 5. 42 Fig.-18 Log probability plots of grain size distribution in Trench No. 8. 47 Fig.-19 Vertical variation in facies in relation to Mean size, S.deviation, Skewness and Kurtosis in Trench No. 8. 48 Fig.-20 Log probability plots of grain size distribution in Trench No. 7. 50 Fig.-21 Vertical variation in facies in relation to Mean size, s.deviation, Skewness and Kurtosis in Trench No. 7. 51 VILL Fig.-22 • The mineral composition of Godavari sediments in Trench No. 1. 57 Fig.-23 The mineral composition of Godavari sediments in Trench No. 2. 57 Fig.-24 The mineral composition of Godavari sediments in Trench No. 3. 58 Fig.-25 The mineral composition of Godavari sediments in Trench No. 4. 58 Fig.-26 The mineral composition of Godavari sediments in Trench No. 5. . 59 Fig.-27 The mineral composition of Godavari sediments in Trench No. 6. 59 Fig.-28 The mineral composition of Godavari sediments in Trench No. 9. 60 IX Fig.-29 The mineral composition of Godavari sediments in Trench No. 10. 60 Fig.-30 Average mineral composition of Godavari sediments. 61 Fig.-31 Map showing variations in flow direction from general flow direction. 64 Fig.-32 Generalized secjuence of Godavari river delta. 70 Fig.-33 Block diagram showing bedforms and stratifcations of the Godavari delta. 71 LIST OF TABLES Page No. TABLE - I Size Frequency Distribution (percent) of Godavari River delta sand 24 TABLE - II Grain size characteristics of Godavari River delta 25 TABLE - III Grain size parameters of sub-population in individual sample 26 TABLE - IV Mineral composition of Godavari sediments 53 TABLE - V Com.putation of vector mean and vector magnitude of cross bedding azimuth 65 XL LIST OF PLATES Page No. PLATE - I Photographs showing trough cross bedding Fig. 1-2 bounded by cross bedding 10 PLATE - II Photographs showing large scale Fig. 1-2 and small scale planar cross bedding 12 PLATE - III Photographs showing parallel laminations 14 Fig. 1-2 PLATE - IV Photographs showing ripple cross laminations 15 Fig. 1-2 PLATE - V Photographs showing climbing Fig. 1-2 ripple laminations, small scale ripples and massive mud 19 CHAPTER I CHAPTER I INTRODUCTION The study of the modern sediments provide valuable information regarding the process and products of the known environments, this information can be of great help in the interpretation of the ancient sequences. Keeping this in view the recent past the attention of sedimentologists have been attracted to the modern sediments specially the river deposits because they are the principal agencies which provide weathered material. These weathered products form sedimentary sequences. Some part of the stream load is deposited on the land, forming alluvial plains and some part is extended towards the sea forming coastal plains and delta. In the present study an attempt has been made to study the sedimentology of delta sediments of Godavari river around Razole. The delta sediments offer excellent opportunity for studying the modern delta environments. The present investigation is an intigrated field study, facies analysis, mineral composition, and flow pattern in a small area with a view to identify various lithofacies and their characteristic features. LOCATION AND ENVIRONS OF THE AREA The study area is approximately 50 sq. Km. It is situated in East Godavari district, Andhra Pradesh (Figl). By and large the major part of the area is covered by alluvium. GODAVARI RIVER The Godavari river which attains a width of considerable proportion about 4.8 Km. down stream of Rajahmundry divides into two primary distributaries at Dowlaiswaram. At Dowlaiswaram, the fluvial system of the Godavari has been effected by a Dowlaiswaram Barrage. The water in the resultant reservoir is distributed by an extensive network of irrigational channels spread over the vast deltaic plain. The primary distributary flowing eastward is known as the Goutami Godavari, where as the one flowing south is known as the Vasishta Godavari. In the lower reaches each of the above two primary distributaries subdivide into several secondary distributaries. Each of these secondary distributary channels empties itself into the Bay of Bengal independently. Fig. 1. Map of the study area and location of trenches. GE0M0RPH0L06ICAL SETTING The Godavari river is the second largest river in India ranking next to the Ganges, rising in the Western Ghats at "TRIAMBAK" at an altitude of 1067 meters above mean sea level near Nasik. The Godavari flows for 900 miles before emptying into the Bay of Bengal. The water resources division of the U.S. Geological Survey (1962) has included the Godavari river in the list of the larger rivers in the world. The river runs across the peninsular India from West to East, and on it's way to the sea it is met by sixteen major tributaries. The Godavari basin is roughly triangular in shape, the major drainage trend of the rivers of the peninsular India including the Godavari is towards the East and South east is due to the uplift of the Western Ghats and slightly tilt of the peninsular India mass to the east during the Mesozoic age Krishnan (1983). METHODS OF INVESTIGATION Field Methods : The area under investigation was divided into ten locations and the data were collected from both the banks. The method employed in the investigation was to dig trenches with the help of a showel and khurpa. The trenches were made without proper orientation to expose the primary sedimentary structures. The depth of the trenches varies from location to location depending upon the height of the sand deposits made by the river during it's flood period. Generally, the depth of the trenches range between 1.5 to 2 meters and the length between 1 to 1.5 meters. After digging, the walls of the trenches were smoothened with the help of a knife. Then the trenches were left for drying by exposing them to air current or sun light. When sediments become dry, the stratifications and other sedimentary structures were visible clearly. Vertical facies of sedimentary sequence were examined in trenches both in longitudinal and transverse sections parallel to flow and sketches were drawn to scale to illustrate different facies,their relationship, bedding type, texture and primary sedimentary structures. In all over 30 samples from various facies were collected vertically at suitable intervals from each trench for laboratory investigation of grain size and mineral compostion. LABORATORY METHOD The grain size analysis was carried out by sieving samples at 4 2 scale of Wentworth using ASTM sieves of 22 cm diameter, twenty five samples from different localities, including three from over bank deposits. In each case 100 grams of sample were sieved for 15 minutes using Ro-tap Sieve shaker and fractions from different sieves were collected. The weight percent frequency and cumulative weight percentage were computed and cumulative weight frequency curves were plotted for each trench. To determine the sediment properties, statistical parameters of size frequency distribution given by Folk and Ward (1957) and Visher (1965,1969) were .computed. The heavy minerals were extracted from eight samples. The material falling in next to model class was taken for heavy mineral analysis. The separation was done according to the centrifuge method of Taylor (1933), using bromoform of specific gravity of 2.89 as separating medium. The heavy mineral crop was washed with alchohol, dried, weighed and mounted permanently in canada balsom. The slides were studied using a swift automatic point counter fitted to a petrological microscope for mineral composition. Since the opinion differed as to the total number of grains that should be counted to obtain a reliable estimate of mineral composition of the given samples Potter and Pettijohn (1963). Successively 200, 300, 400 and 500 grains were counted from randomly selected slides. It was found that counting of 100 to 300 grains per slide was sufficient. However 200 grains per slide were counted for determining the total model composition of the sands. CHAPTER II CHAPTER II FACIES DESCRIPTION The term facies was introduced by Gressly in 1830. Gressely and Prevost in (1638) recognised various sedimentary facies on the basis of lithology in Jurassic in Eastern France. De Raff et al, (1965) introduced common usage of facies on the basis of lithology, structure and organic aspects of cyclecal representation in a number of facies. During the last few decades fluvial sediments have been extensively studied in known environments with special reference to various sedimentary facies. (Mial, 1980; Walker; 1980; Jackson; 1976; Middleton; 1978; Klovan; 1964; Young, 1975). These studies have been used to understand the ancient sediments and the environments of deposition responsible for their deposition . A single example of present day variation in physiochemical and organic setting of sedimentation illustrates facies in the stratigraphic record to define the specific sedimentary environment. In the present study an attempt has been made to recognise facies on the basis of lithology, primary sedimentary structures, particularly in the studies of modern depositional environments. Delta models have been discussed and developed by Coleman and Wright, 1975; Galloway, 1975; Reading, 1978; and Walker, 1976. Three dimensonal facies models, was suggested by Allen (1965) for meandring streams and braided streams of Donject type was described by Mial (1977). Willings and Rust (1969) and Doeglas (1962) described the modern streams while Cant and Walker (1976), Killing (1968), and Steel (1974) described models from the ancient sediments. Mial (1985) proposed a classification based on eight architectural elements for the fluvial sediments. The facies code consist of two parts in that prefix indicate dominant lithology and a suffix for sedimentary structure in each facies. In the present study seven different facies were recognised in the vertical sections in the trenches on the basis of grain size, bedding type and sedimentary structures. The facies recognised were coded individually following Mial (1985). COARSE TO MEDIUM SANDY FACIES 1 Trough crossbedded sandy facies,(St) 2 Planar cross bedded sandy facies, (Sp) 3 Ripple cross-laminated sandy facies, (Sr) 4 Horizontal bedded sandy facies, (Sh) 8 FINE GRAINED FACIES 5. Parallel laminated fine sandy facies, (Fl). 6. Lenticular sandy facies, (SI) 7. Massive silt and clay facies, (Fm). COARSE TO MEDIUM SAND FACIES Trough cross bedded sandy facies (St): Trough cross bedded facies occurs interbedded with planar cross bedded facies, plate I (Fig.l & 2). The individual units range in thickness from 8 to 50 cm. ( > 4 cm. thick, Reineck and Singh 1980). Large scale stratification are abundant. In vertical sections parallel to current flow, troughs are well depicted by scours and in these sections traces of foresets are commonly symmetrically curved and tangential to the underlying erosional surfaces plate I(Fig.l & 2). In most trenches foreset angle is about 141 and the scale of cross bedding is about 25 to 50 cm. The large scale cross stratification in lower part of the sequence comprises coarse sand. The average grain size of the facies is decreasing in the down stream. The formation of cross bedding is controlled by current velocity, flow characteristics and the rate of sediment supply. The large scale cross bedding (>4 cm) occuring in Cosets, are formed by the down stream migration of a symmetrical mega ripples, dunes and sand waves Allen (1962 ; 1963) Jopling (1963). PLATE - I Jig.l. Showing trough cross bedding bounded by planar cross bedding. Pig.2. Showing trough cross bedding and horizontal bedding. 10 Mckee (1957b), Lahee (1952) suggested that scour and filling are responsible for the formation of trough cross bedding. Scour filling is due to down stream migration of ripples. Cosets of trough cross stratification indicate unidirectional flow with appropriate range of water depth and velocity to form three dimensional large ripples, Singh, I.B. (1977); Reineck and Singh, (1986), Large scale cross stratification can be formed by infilling of scour pockets related to migrating the lee face of advancing dunes, Jopling (1963). According to Harms et al (1963), the mechanism of scouring and infilling of the scour pockets develop a tangential variety of stratification due to velocity and high depth ratio. The periodic occurance of fine grained material within the sets, with truncational characteristics and tangential contacts suggest a temporary, periodic increase in current velocity, resulting in an increased supply of suspended material. Discontinuties within the large scale cross stratification may be related to grain size variation during transportation. Jopling (1963). Planar cross bedded sandy fades (Sp): Planar cross beds as large in solitary sets and cosets plate II(Fig.l & 2). The mean thickness of sets decreases vertically from 85 to 19 cm, from bottom to top of the sequence in most of trenches. 11 PLATE - II Pig.l. Showing large scale cross "bedding. Pig.2. Showing smt*ll scale planar cross bedding. In channel sand bodies of this facies, the overlying and underlying surfaces are erosional. The large planar cross stratification units thickness range from 26 to 75 cm, these planar cross stratifications were also observed to be inclined normally in the current direction. According to Harms et. al, (1982) planar cross stratification may be deposited by migrating two dimensional large ripples. Allen (1963) concluded that cosets of planar cross beds are formed by migration of a symmetrical ripple having straight and parallel crets and the scale of strata is grouped on the basis of amplitude of the ripples. Planar cross stratification are alphatype (Allen, 1963). They are sharp at scoured bases and tops, set thickness ranges from 5 cm to 5 m, grain size and sorting characteristics are similar to St facies Mial (1977). The more common planar cross bedding consist > 30 cm thick units and the bounding surfaces of the set laminae become tangential. A cross bedding surface more or less common is called planar cross bedding Reineck and Singh (1986). Horizontally bedded sandy facies (Sh) Horizontally bedded sandy facies show inclination less than 4 degrees plate III(Fig. 1 & 2). The thickness increases laterally, colour of this facies is grey and the grain size is fine to coarse. Individual beds are generally 13 PLATE - III 1 Pig.l. Showing r)arallel laminations in medium sand. equal to subequal in thickness and locally contain lenticular bedding. The Sh facies displays mica flakes along its laminae. The bedding surfaces are generally devoid of ripple marks, indicating deposition by relatively high velocity flow regime. Bridge, (1978) described the origin of horizontal bedding under turbulent boundary layers. The formation of horizontal laminated facies can also take place under two different conditions, ie. in shallow water and during flood stage Mial 1977. The deposition may be attributed to an increase in flow regime due to local shallowing of the basin floor and seasonal increase in discharge or to sheet like flood (McKee et al. , (1961). Horizontal stratification consist of coarse sand may be interpreted as indicating transportation in planar sheets under high energy conditions Casshyap and Kumar (1987), Desloges and Church, (1987). According to Coleman (1969), horizontal stratification are formed by rapidly migrating trains of exceptionally small bed forms. Ripple cross laminated sandy facies (Sr) : The ripple cross laminated facies consist of coarse sand and thick beds, plate IV(Fig.l & 2). The thickness of this facies ranges from 20 to 60 cm. The thickness decreases vertically. In most of the trenches, Sr facies 15 PLATE - IV Pig.l. Showing ripple cross laminati stratification. ons au base and planar Fig, 2, SJiowxii^ ripiol e cross laminations and trough cross bedding, 16 overlain by trough cross stratification. The crest of the laminae are inclined in the direction of current flow. The angle of inclination ranges from 8| to 201. Individual units may have perhaps deposited by waning flood. Ripple cross laminations are developed, when the excess suspended sediment is continuously available for deposition which is deposited above the earlier formed rippled layer Reineck (1963), McKee (1965), Singh and Kumar (1974). The ripple cross laminations in which laminae is in phase are interpreted, as the result of abundant supply of sediment in suspension , no erosion on stoss side takes place and laminae is in phase are completely, buried and preserved. The ripple laminae is in phase are produced only when angle of climb is greater than the stoss side slope. The ripple cross lamination marked with high angle of climb, indicates high rate of deposition which may have resulted from deceleration of flow, with a corresponding increase in sedimentation as occurs during waning stage of floods Lindholm (1987). Climbing ripples may be produced by straight crest, undulatory or small linguoid current ripple or even by wave ripples Reineck and Singh (1986). 17 FINE GRAINED FACIES Parallel laminated fine sandy facies (Fl) : Parallel laminated structures are sets of laminae in which individual laminations are parallel to the lower set boundary Harms and Fahnestock (1965). The structure is commonly observed in fine sand and silt. The laminations show alternating dark and light colour bends. The thickness of the laminae ranges from 1 to 1.5 cm. The laminations do not show any kind of undulations. This structure is mostly observed in over bank deposits plate V (Figl). Parallel laminations are developed in fine sand and silt. The fine sand parallel laminations is formed when the flow velocity is high and water depth is shallow under upper flow regime. When such conditions exist the ripples and dunes are destroyed, in such conditions water surface is smooth like glassy appearance (Collenson and Thomson 1982). Lenticular sandy facies (SI) : This facies is marked by the presence of ripples, and well developed in bank deposits. The thickness of the set comprising the laminations of silt and clay ranges from 10 cm to 25 cm. Each laminae mud is about 4 cm thick. The height of the ripple ranges from 1.5 cm to 3 cm and length of the ripple varies from 15 cm to 20 cm. 18 PLATE - V ?ig.l. Showing climbing ripple laminations from overbank deposits. Pig,2. Showing small scale ripples in silt under massive mud, 19 Lenticular bedding may develop by current or wave action depositing the sand alternating with stack water conditions, when mud is deposited Reineck (1960a,b). The sand lenses are made up of foreset laminae of current ripple, when ripples migrate a muddy substance, the supply of sand or silt is laminated, the isolated ripple trains as lenticular bedding may be preserved Lindholm (1987). Therefore it is interpreted that the lenticular laminae were developed due to fluctuations in the current velocity. Unsteady sediment transport associated with the turbulent brushing process formed the lenticular laminae Bridge and Best (1988). Massive silt and mud facies (Fm): Massive silt and muddy facies may have been deposited by suspended load after the flood and may be interpreted as over bank flood sediment plate V(Fig.2). This facies may also associated with minor creavas splay deposits, mud layers gives idea about the number of flood episodes occured during the deposition of particular sedimentary unit. These facies occupies the top portion of the bank deposits and generally lying above the cross bedded sandy facies. The thickness of this facies goes up to 4 m at some places. Massive units are the result of rapid sediment supply from high energy flows Fielding (1986). Massive units may be interpreted as the result of sediment transportation in 20 planar sheets under very high energy conditions. Rust (1972) and Lindholm (1987), described massive units formed by sedimentary gravity floods which lack a mechanism to produce primary structures. The structures are destroyed due to upward movement of pore water by bioturbation mollted nature of concentrations present in the sandy massive units, indicate the product of post depositional phenoraenon silt and clayey massive units are interpreted as having formed by heavily laden water current during waning periods of floods stage. Similar interpretation of massive units having fine sand and silt representing rapid deposition by suspension fallout from possible flood flows Morison and Hein (1987). 21 CHAPTER III CHAPTER III DISTRIBUTION OF GRAIN SIZE IN RELATION TO SEDIMENTARY STRUCTURE General: Grain size distribution of sediments are important tools to understand the process and products. During last few decades the environment of deposition has been described on the basis of grain size distribution (Folk and Ward, 1957; Mason and Folk, 1958; and Friedman, 1961; 1979). The statistical parameters such as mean size, standard deviation, skewness and kurtosis of fluvial environment were developed and described to understand the fluvial processes.Inman(1949) distinguished three populations (traction, saltation and suspension) on the basis of shape and size of sediments. Moss(1962;1963;1972) using the shape and size of the grains distinguished subpopulations in traction, saltation and suspenions. He further opined that fine sediments transported in suspension usually have an upper size limit of about 0.07 to 0.1 mm, saltation have an upper size limit of about 0.25 to 0.17 mm and traction have an upper size limit 0.5 to 0.25mm. Ten trenches were dug in study area to study the vertical and lateral variation in grain size distribution. Samples were collected from Tatipaka, Razole, Sivakodu, Rama 22 Raju Lanka, Sakinetipalli, Rameswaram, Doddipatla, Elamanchilli, Chinchinada and Narsapur (Fig.l). The data is listed in Table I. Cumulative frequency curves were plotted on log probability paper following Visher (1965;1969). The grain size distribution was grouped broadly into three types of probability plots mainly on the basis of number of subpopulations and their percentage and sorting. The mean size sediment ranges from 2.6^ to 0.03 0. Out of 23 samples 11 samples show medium sand, 8 samples are coarse, 3 samples are fine and 1 sample is very coarse Table II. The mean size of overbank deposits ranges from 2.1 ^ to 1.9^ . Out of 3 samples, 2 samples are fine sand and 1 sample is medium sand. Inclusive graphic standard deviation values of the samples under study range from 1.4 0 to 0.4ffl . Out of 23 samples, 13 samples were moderately sorted, 5 samples moderately well sorted, 4 samples poorly sorted and 1 sample well sorted Table II and III. Out of 3 overbank samples, 2 samples were poorly sorted, 1 sample moderately well sorted. Sorting of sediments depends upon competency and stability of currents. If currents are relatively of constant strength, sediment will be moderately sorted to well sorted, but fluctuating current will give rise to poor sorting. 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OL a. a. a. a. a. u CM cn in r^ . vo CT> o o en CM CM en \o O O m 00 en o .-I ^ CM CM ^ CM T-t CM CM »-* '^ O^ iH CM CM m cn s:j \0 CM CM en T-t CM CM '-f en CM en i-l CM CM CO en en ~* CM CM en %* en rsj m m O O CM r^ r^ O CM CM in m in mom en O O O r-l i-l O d 1-t *-* »-t ( ,H O O o ^ o CM O O I d 8<- z Z z a. w o oi ai a Bi a: Q Q 06 O J Q a -J O Q Q a. »-i »-( o O w O O o ^ O o o J O o o < < o o < O O >-, o u < o U O o_ o b) O o o I b. b. U 0. b O O u o o o < o U b. O O O a. o o « X X b. O M z z u. h-ol l-ol O a. a. m n en 0^ (M oo f-l t-( O O O m o m m m en m I-H m m m en 00 m en vo -3 mm \o vo m r^ m en r^ \o vO ^ sO ^ lO \0 m M Z Z o: o O W M d W < < ZOO 00 < z z -3 • -3 u O O O m N O; U w 5 Z O t-1 o o M O >-< O (b m in o 2 z U bl -: Q Q a oc J a H J O O o o O _J o ae oJ O O o o c o o U I U a. I a. < < u O I to u o b, b. X z X i o U (7^ in CM CM o m o in r^ < t en f^ m I f- in ^ I in OC CM o QC en 1 CM r 1 1 en in I 1 I -^ 1 1 1 1 { < OQ U < CO < OQ O < CO < to o < OQ O CQ < DO en < eM CM en en en in in in lO 00 o o o oc t—< T-l o CM en in 00 H H H 1- H 26 indicate currents of moderate competency and persistency. The inclusive graphic skewness (Skj^) values of the samples under study area ranges from -0.07 pf to + 0.2 d. Kurtosis values of the studied samples range from 2 d to 0 . 8 f^ . Ripple cross laminated sandy fades (Sr) R.G. Walker (1963) has recognised three distinct types of ripple-drift cross laminations in upper carboniferous formation in S.W. England. Type I: It is characterized by strong erosion of laminae on the stoss side of the ripples and absence of grading. Type III : It is characterized by an absence of erosion on the stoss sides. Concentration of mud in the ripple troughs and an upward gradual decrease in grain size and ripple amplitude. Type II: It is an intermediate form with some characteristics in common with type I and III. He suggested that type I is formed in fluvial and shallow water environments at a time of net deposition of sediment Type III formed by turbidity currents. Type II suggests hydrodynamic conditions intermediate between fluvial or shallow water traction and turbidity currents. Ripple cross laminated sandy facies was analysed for grain size at Tatipaka trench. Where this facies is well 27 developed seven samples were analysed (Tablelll). The bulk of each sample from Sr facies showing two to three populations (saltation, suspension or traction, saltation, suspension) at lA, 2A, 5A, 9B and lOA samples (Fig.2-11), consist three populations and 3A and 4B, samples consist two populations (Fig.12-15). Sediment size of inflection points of three population samples at coarser end between traction and saltation range from -1.25 gf to 0.0^ and for those at finer end between saltation and suspension from 2.5 of to 5.0 0. The inflection points in two populations coarser ends is -0.25 0 to -3.9 0 and finer end is 5.0 0 , the above data suggests the sediment load of Sr facies has been transported largely by saltation and contains about 60 to 99 percent whereas traction load comprises about 10 to 38 percent and suspenstion load 0.5 to 3.7 percent. On the basis of above results, the bulk of the sediment of this facies was deposited under low flow regime conditions (Mial, 1978). Overall the sand of Sr facies have a mean size (Mz) ranging from 0.53 0 to 2.43 0 with standard deviation (CTI) 0.76 0 to 1.110, suggesting that the sediment is moderately well sorted to poorly sorted, Skewmess (Skj^) ranges from - 0.14 ^ to 0.28 0, coarse skewed to fine skewed and Kurtosis (Kg) from 0.82 r^ to 1.550 platykurtic to very leptokurtic. 28 99 99 u < u < > zu 111 o u cc (1. Ill > 3 -2.0 1.0 2.0 3.0 4.0 5.0 GRAIN SIZE IN PHI UNITS Fig. 2. Log probability plots of grain uize distribution in Trench No. 1. 29 99.99 U) -I < o CD < OD O a z Ijj 3 Z -2.0 1.0 2.0 3.0 ^.0 GRAIN SIZE IN PHI UNITS Fig. 3. Log probability plots of grain size distribution in Trench No. 2. 30 00 I ? 0.75 a a111 15"- -i i-L. • • ' J U_ 0.01 0.1 1.0 0 0.01 01 1.0 0 0.01 01 10 0 0.01 0.1 1.0 2 00 MEAN SIZE S.DEVIATION SKEWNESS KURTOSIS (Mz) (0^1) (SKI) (KG) Fig. 4. Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench 1. 001 ua. t- Ul Z 10 a ou 2 0 001 01 1.0 2 000 01 0.1 10 2 00 15 OS 0.5 0 001 0.1 10 200 MEAN SIZE S.DEVIATION SKEWNESS KURTOSIS (Mz) (O-I) (SKI) (KG) Fig. 5. Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench 2. 31 99 99 u —I < o ffi < CD O a z Ul o tr a11.1 o>• z UJ O UJ z -2.0 -1.0 00 1.0 2.0 3.0 4.0 GRAIN SIZE IN PHI UNITS Fig. 6. Log probability plots of grain size distribution in Trench No. 5. 32 00r rjrw »/> (T u •- u z 2 0251 X a. UJ o -L. J I I I is"- 0010.1 1.0 2.000.01 0.1 1.0 2.00-1.5-0.5 0.5 0 001 0.1 1.0 2 00 MEAN SIZE S.DEVIATION SKEWNESS KURTOSIS (Mz) (O-I) (SKI) (KG) Fig. 7. Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 5. 33 99.99 < CD < m o a a. z hi u CE Ul a bJ 3 a u cr > 3 3 -1.0 00 1.0 2.0 3.0 4.0 5.0 GRAIN SIZE IN PHI UNITS Fig. 8. Log probability plots of grain size distribution in Trench No. 9. 34 99 99 -J < 01 < CD a.o 0. z a. UJ 0. >- oz iij O bJ oc b. > Z o -2.0 -1.0 00 1.0 2.0 3.0 40 5.0 GRAIN SIZE IN PHI UNITS Fig. 9. Log probability plots of grain size distribution in Trench No. 10. 35 ao K III •- U 1-0 tei O 1.0 J J. L JL L JL 0.010.1 1.0 2 000010.1 1.0 2.00-1 S -OS O.S 0 0.010.1 10 200 MEAN SIZE S.DEVIATION SKEWNESS KURTOSIS (Mz) (a-l) (SKI) (K6) Fig. 10, Vertical variation in facies in relation to Mean size, S. deviation, Skev/ness and Kurtosis in Trench No. 9. aor z 5 1.0 X 0. w o 2X) JL I.S 2.0 2.500.1 1.0 2u0. 0 -1.S-0.S OS 0 0.1 10 200 MEAN SIZE S.OEVIATION SKEWNESS KURTOSIS (Ml) (O-II (SKI) (KG) Fig. 11. Vertical variation in facies in relation to Mean size, S. deviatideviationi , Skewness and Kurtosis in Trench No. 10 36 9999 < 0 < (D O a. a z UJ a. bi 3 O UJ a. > 3 00 1.0 20 3 0 4.0 GRAIN SIZE IN PHI UNITS Fig. 12. Log probability plots of grain size distribution in Trench No. 3. 37 99.99 UJ < o CD < CD O a. a. u cr UJ Q. >- UJ > 3 -2.0 -10 00 1.0 2.0 3 0 4.0 GRAIN SIZE IN PHI UNITS Fig. 13. Log probability plots of grain size distribution in Trench No. 4. 38 001 111 z z X a bi O 15' JL 0.01 0.1 10 2.000.01 0.1 0 200-1.5-0.5 0.5 0 0.01 0.1 1.0 2.0 0 MEAN SIZE S.DEVIATION SKEWNCSS KURTOSIS (MI) (O-I) (SKI) (KG) Fig. 14, Vertical variation in facies in relation to Mean size, S. deviation, Skev/ness and Kurtosis in Trench No. 3. 0.0 r lit u z 075 a u o * I I I 15«- _i_ _l_l 0010.1 10 2.0000101 10 0 0 01 01 100 0.1 1-0 2 0 3.0 ( MEAN SIZE S. DEVIATION SKEWNESS KURTOSIS (Mz) ( Fig. 15. Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 4. 39 Planar cross bedded sandy fades (Sp) The planar cross bedded sandy fades (Sp) have been observed in all the trenches. The similar fades have also been reported by Frazier and Osanik (1961) from point bars of Mississipi river, Harms et al.(1963) in Red river, Lousiana, McKee(1938) in the flood plain deposits of the Colorado river, Arizona, Coleman(1969) in the channel bar sediment of the Brahmaputra river. The floods may have formed the sandy layers as indicated by trough cross lamination. The probability plots of eight samples collected from different trenchs of Sp fades exhibit two to three populations (Fig.2-17). This fades is well developed in trenches and exposed sections at Rama Raju Lanka. The sediment size corresponding to inflection points at coarser end between traction and saltation ranges from -1.25 0 to 0.7^ and for those at finer end between saltation and suspension from 1.90 0 to 5.0 0 . The bulk of sediment load consists of traction 16 to 64 percent, saltation 70-90 percent load. Suspension load occurs in subordinate type 10 to 16 percent. Overall sand is medium size with mean size (Mz) ranging from 0.03 0 to 1.90 0 and standard deviation (cj-I) ranges from 0.45 0 to 1.010 poorly sorted to well sorted Skewness values showing that the sediment is coarse skewed to fine 40 99.99 99.9 99.6 -99 UJ -J 98 < o 95 90 0 60 tL 70 60 t£ Ui - 50 a. >• 40 z UJ H30 o UJ (T 20 U. UJ > 10 3 2 1 0.5 0.2 0.1 005 JL -L _L J_ 00 •2.0 -1.0 0.0 10 20 30 40 50 GRAIN SIZE IN PHI UNITS Fig. 16. Log probability plots of grain size distribution in Trench No. 6. 41 OOr (T U t- Ui z 5 10 z a bJ o -I- -i- zo"- "* 1.0 2 0 3.0 0 0.1 10 2.0 0 1.5 0.5 0.5 0 10 2.0 3.0 4 00 MEAN SIZE S.DEVIATION SKEWNESS KURTOSIS (Hz) (O-I) (SKI) (KG) Fig. 17. Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 6. 42 skewed and range from SKj^ -.06 d to 0.23 gf, and kurtosis ranges from (KQ) 0.1 0 to 2.02 d mesokurtic to very leptokurtic. This facies at Rama Raju Lanka the sand deposit is medium sand with mean size (Mz) 1.31^. Moderately sorted(Q- I) 1.01 (^, near symmetrical SKj^ 0.06j^, and very leptokurtic KG 2.013^ . The average of eight samples of planar cross bedded facies shows that the sand facies comprises of medium sand (MZj) 1.06 (^, it is moderately well sorted ((j-I) 0.90 j^, fine skewed (SKj^)O.ll^ and leptokurtic (KQ) 1.11 d. Trough cross bedded sandy facies (St) : Trough cross bedded sandy facies occurring in the study area results from infilling of trough shaped scours by migrating dunes (Fig.12-17,19,21,22) The type of dune and it's association with scours are still controversial. Allen, (1963, 1965); Harms and Fahnestock, (1964). A better understanding of large scale cross bedding in a unidirectional current regime Jopling (1963). Harms et. al. (1963) stated that the mechanism of scouring and infilling of the scour pockets developed a tangential type of cross stratification in relatively high velocity and a high depth ratio. 43 The cumulative probability plots of sand facies with large scale trough cross bedding for grain size analysis of five samples in the study area collected, at Tatipaka, Sivakodu and Razole, show intersecting plots with one or two inflection points. The first inflection point between traction and saltation range from -1.25 Of to 2.5 J^f and second point from saltation and suspension lies between 1.3 (^ to 5.00^ . The bulk sediment load consists of traction 10 to 77 percent, saltation 35 to 65 percent and suspension load occurs subordinate type 5 percent. This facies consists mostly of coarse sand with mean size (Mz) varying from 0.23 Cf to 1.23j^ ; moderately sorted Ca~I) 0.710 to 1.23^. It is near symmetrical (SKj^) 0.006^ to 0.028 0) and commonly mesokurtic (KG) 0.78 of to 1.41^. At Tatipaka, Sivakodu and Razole the large scale trough cross bedded sand facies is coarse grained (Mz) 0.822^ moderately sorted {0~ 1) 0.31 C . It is fine skewed (Sj^j^) 0.035 (/i and mesokurtic (KQ) 1.00 0. Horizontal bedded sandy facies (Sh) Horizontal laminations in turbidites may be related to migration of long wave length antidunes, Middleton and Hampton (1973), Moss (1972). Horizontal bedding can develop at all motion intensities from the small ripple stage. The mega ripple stage, while due to flow unsteadiness, 44 bedforms sometimes fail to develop. The horizontal bedded sandy facies (Fig.26-27) graphic plots of cumulative weight percentage yield two sediment populations, saltation and suspension. The saltation populations constitutes 98 percent, supension 1.3 percent. The sediment size at inflection point at coarser end, between saltation and suspension 0.5 0 to 3.5fij an d for those at finer end, 3.5^ to 5.0 ^ . The facies is fine grained with mean size (Mz) 2.0 ^ moderately well sorted (cj-I) 0.69 (^, symmetrically skewed (Sj^j^) 0.02 (^ and mesokurtic (KQ) 1.05 (J. Lenticular sandy facies (SI) This facies is well developed at Rameswaram, statistical parameters of this facies showing two populations saltation and suspension(Fig.28, 29) . The sediment size corresponding to inflection points at coarser end between 0.5 0 to 4.25 0 and for those at finer end between 4.25 (^ to 5.00 0 . The sediment load consist of saltation 98 percent and suspension 1.3 percent. Sand size is fine grained with mean size (Mz) 2.67 (^, standard deviation (Q- I) 0.69 ]? moderately well sorted; near symmetrically skewed (Sj^j^) 0.01 (^ and kurtosis (KQ) 3.42 (^ is leptokurtic. 45 Parallel laminated fine sandy facies (Fl) Veiry small scale ripple fine sand facies was analysed for grain size at Elamanchilli trench (base of overbank deposits). One sample was analysed (Table III) and data were plotted on log probability paper as shown in (Fig.18,19). The sample from Fl facies consist of two populations (saltation and suspension). Sediment size corresponding to infelection points at coarser end between saltation and suspension ranges from 1.0 J3 to 4.1 of and for those at finer end, ranges from 4.1^ to 5.0 ^. It constitutes 98 percent saltation load and 1.0 percent suspension load. It may be inferred that sediment load of Fl facies has been transported largely by saltation load. The mean size of Fl facies is (Mz) 2.7 p fine sand, with standard deviation ^I) 0.68^ moderately well sorted, skewness (Sj^j^) 0.090 (J fine skewed; and kurtosis (KQ) 0.778 ^ platykurtic. Massive silt and clay facies (Fm) This facies is well developed in overbank deposits of Godavari river. Probability plots of two samples exhibit two populations saltation and suspension. Sediment size of inflection points at coarser end of saltation and suspension 0.5 m to 3.5 0, and those at finer between 3.5 46 99.99 99.9 996 • ^- 99 98 < o 9S 90 < OD O 80 a a. 70 60 o a SO III a. 40 y- 30 3 O Ui 20 a 10 z O 2 ; 1 0.5 0.2 0.1 OOS Joo -2.0 -10 1.0 2.0 3.0 *0 GRAIN SIZE IN PHI UNITS Fig. 18. Log probability plots of grain size distribution in Trench No. 8. 47 00 r (A a. ill »- Uzi 20 a. otii t M • I 4.0' 0.010.1 10 2.000.010.1 10 2.000.010.1 10^ 0.01 0.1 1.0 0 MEAN SIZE S.DEVIATION SKE\WNESS KURTOSIS (Mz) (o-I) (SKI) (KG) Fig. 19. Vertical variation in facies in relation to Mean size, S. deviation, Skewness and Kurtosis in Trench No. 8. 48 0 to 5.0 0 (Fig.20;21). These samples constitutes saltation load 64 to 71 percent and suspension load 27 to 37 percent. This facies is consists of fine sand with mean size (Mz) 1.96 0 to 2.67 0, poorly sorted (orl) 1.005 ^ to 1.447 0". It is coarse skewed to fine skewed (Sj^j^) 0.176 ^ to 0.288 0 and mesokurtic to leptokurtic (Kg) 0.91 0 to 1.19 d. Vertical variation in grain size : As per cumulative plots, the verticle variation in grain size shown at various down stream localities along the distributary channels of Godavari. The mean sand size is increasing upward from 0.53 0 to 2.49 0 at the base, 0.033 0 to 2.67 0 middle part and 0.233 0 to 2.0 0' at the top. All trenches show two cycles of sediments occurring in the 1.5 to 2.0 meter thick seguence. The grain size parameters exibits a slight vertical variation in most trenches. However, there is a tendency of increasing mean size from base to surface. The grain size characters show distinct change in sorting. The lower part of the sequence is poorly sorted and the middle part is well sorted, whereas the upper part again show poor sorting. 49 99.99 u < ffi < CD O CC a. IE a. UJ a3 u b. UJ > 3 Z •2.0 -1.0 0.0 1.0 2.0 30 4.0 GRAIN SIZE IN PHI UNITS Fig. 20. Log probaility plots of grain size distribution m Trench No. 7. 50 0.0 Ui SKl -0 17 UJ KG 0.91 Z z 1.5 a obJ 3.0>- Fig. 21. Vertical variation in facies in relation to Mean size, S. deviation, Skevmess and Kurtosis in Trench No. 7. 51 CHAPTER IV CHAPTER IV MINERAL COMPOSITION OF 60DAVARI SEDIMENTS. Twenty samples spreading all over the area under investigation were examined for determining the mineral composition and other petrographic characters. The volumetric proportions of the sediments is listed in Table IV The following minerals were recognised from the samples collected from various localities; quartz, opaques, garnet, amphiboles, pyroxenes, sillimanite, kyanite, staurolite, sphene, epidote and zircon (Fig.22-29). Quartz : Quartz is most prominent mineral and on an average 20.54 percent in Godavari river sediments. Generally grains are angular to subangular but some in grains rounded out lines are common. The angular grains show fractures, while subrounded grains are marked with smooth surfaces. The grains show straight/wavy extinction. Opaques: Opaques are most abundant of all the minerals and comprised on an average 27.58 percent of the sediments. Generally, opaques are subrounded to subspherical. In plane polarized light most of the grains are dark coloured. Garnet: Majority of garnet grains are subrounded to sub spherical. Two varieties of garnets were recognised, almondite type showing pink or purple red colour and 52 TABLE:- IV MINERAL COMPOSITION OF GODAVARI SEDIMENTS. SAMP. /WHiaOLES No. ACTINXI7E/ aJART7 OP/XaJES GAWET HOfitaflO HYPER- DIOP- SILLIM- IOTA- STAURO- SPHBC EPI- ZIR- TOTACC tme SIDE ANITE NITE QTE DOTE CON 1 28.10 24.« M.fB 22.28 1.80 1.24 4.65 0.50 - - 0.75 0.30 97.76 2 21.55 21.51 18.26 20.12 0.95 0.46 3.71 1.0 0.65 0.25 1.50 0.25 90.21 3 27.61 18.75 20.40 16.Z3 1.87 1.06 5.0S 0.33 0.50 0.33 1.06 0.45 93.64 4 20.0B 26.07 16.76 21.03 1.06 1.10 4.03 1.15 0.58 0.35 1.36 - 92.52 5 18.13 24.73 5.64 22.36 0.48 1.03 6.47 0.11 0.69 0.24 1.49 - 81.35 6 13.30 42.76 16.81 9.95 1.25 1.16 2.03 0.27 0.79 0.26 0.95 1.40 90.91 9 15.95 33.Z3 12.05 20.80 0.85 0.75 4.60 0.31 0.56 0.09 1.85 2.00 92.92 10 19.64 29.20 16.30 18.65 2.37 0.70 6.00 - 0.25 - 1.13 0.12 94.36 Avg. 20.54 27.58 14.98 18.92 1.32 0.93 4.56 0.52 0.57 0.25 1.26 0.75 53 grossutorite showing light brown colour. It constitutes on an average 14.98 percent in composition (Fig-30). Amphiboles: (a) Actinolite: Grains are fresh and unaltered. The colour of these grains showing green to greenish blue. The grains are subangular to subrounded in shape. {h) Hornblende: The hornblend grains are greenish brovn to light brown in colour and are elongated. Hornblend grains displaying pleochroism in shades of dark brownish red are rarely observed. The average percentage of amphiboles is 18.92 in Godavari river sediments (Fig.30). Pyroxenes: (a) Hyperthene: Generally hyperthene is prismatic in shape. It commonly displays light green to purple pleochroic scheme and green to greenish yellow. It constitutes on an average 1.32 percent in the sediments (Fig 30). (b) Diopside: Diopside grains are subrounded to well rounded. Colour of these grains are in shades of light grass green in pleochroic scheme. It constitutes on an average 0.93 percent (Fig.30). Sillimanite: One set of prismatic cleavage is very common in sillimanite grains. Large grains showing inclusions of 54 quartz and opaques. Most of the grains are subrounded. The average percent of sillimanite in Godavari river sediments is 4.56 (Fig.30). Kyanite: In kyanite, grains show two sets of prismatic cleavage. They are generally colourless and rarely showing light blue colour. A few rounded grains are observed. It constitutes on an average 0.52 percent (Fig.30). Staurolite: Staurolite grains are prismatic. The grains display two types of pleochroic schemes. One deep rust brown to honey brown, and the other orange to yellow. Most of the grains show straight extinction. Inclusions are rarely observed. The average composition of staurolite in Godavari river sediments is 0.57 percent (Fig.30). Sphene: These grains occur either as irregular or sub rounded, grains showns brown in pleochroic scheme. Number of irregular cracks are commonly observed and on an average constitutes 0.25 percent (Fig.30). Epidote: Epidote commonly occurs as subrounded to irregular grains in shape. Most of the grains display distinct pleochroism either bright green grass to greenish yellow, few grains showing shades of olivine green in pleochroic scheme. It constitutes on an average 1.26 percent in Godavari river sediments (Fig.30). 55 zircon: Most of the zircon grains are either euhedrai or subhedral in shape. These grains are not showing any growths, few of the grains have corroded prismatic faces, perfect crystals which either prismatic or prismatic pyramidal are common, indicating euhedrai grains show variation in colours and are rounded. Zoning is common in these grains are free from inclusion and constitutes on an average 0.75 percent in Godavari river delta sediments (Fig.30). 56 Fig. 22. The mineral composition of Godavari sediments (in percent) in Trench No. 1. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphibol- es; (5) Hyperthene; (6) Diopside; (7) Sillim- anite; (8) Kyanite; (9) Epidote; (10) Zircon. Fig. 23. The mineral composition of Godavari sediments (in percent) in Trench No. 2. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphibo- les; (5) Hyperthene; (6) Diopside; (7) Silli- manite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon. .c-^ mil0.30(10 ) Fig. 22 0.25(12) Fig. 23 57 Fig. 24. The mineral composition of Godavari sediments (in percent) in Trench No. 3. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon. Fig. 25. The mineral composition of Godavari sediments (in percent) in Trench No. 4. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote. 0.3302) .33(11) Fig. 24 K> 0.35(11) 0.58(10) ^< P Fig. 25 58 Fig. 26. The mineral composition of Godavari sediments (in percent) in Trench No. 5. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote. Fig. 27. The mineral composition of Godavari sediments (in percent) in Trench No. 6. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon. ^o^€- 0.11(11) Fig. 26 o Fiy. 27 59 Fig. 28. The mineral composition of Godavari sediments (in percent) in Trench No. 9. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon. Fig. 29. The mineral composition of Godavari sediments (in percent) in Trench No. 10. The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Staurolite; (9) Epidote; (10) Zircon. |0.09(12) 0.31(11) '0,560o; % s/ Fig. 28 Fig. 29 60 Fig. 30. Average mineral composition of Godavari sediments (in percent). The numbers in parenthesis are designated as follows: (1) Quartz; (2) Opaques; (3) Garnet; (4) Amphiboles; (5) Hyperthene; (6) Diopside; (7) Sillimanite; (8) Kyanite; (9) Staurolite; (10) Sphene; (11) Epidote; (12) Zircon. 0.25(12) 0.5?()i) Fig. 30 61 CHAPTER V CHAPTER V FLOW PATTERNS Sorby (1859) was the first to systematically measure the cross-stratification, but did not publish.Brinkman (1933) was the first to give a clear concept of paleocurrent study. Potter and Olson (1954) used the cross-stratification as a tool for determining the paleocurrent. Recent studies of the dispersal patterns and basin analysis with the help of primary sedimentary structures of modern environments, were taken by Williams (1971), Picard and High (1973), Smith (1970), Coleman (1969) and Killing (1969). The present study aims at recognition in variation in flow patterns with the help of primary sedimentary structures (cross stratification). Suitable trenches were selected in the down current direction and orientation of the cross-bed foreset planes were recorded. Two types of cross-stratifications namely plain and trough are occurring in the study area. In case of planar cross-stratification, dip azimuths were directly measured with the help of clinometer compass, whereas for the trough cross-stratification, azimuth of the acute bisecrix of the curved surface was taken as a true azimuth of the foreset surface. A total of 415 measurements of the cross- stratification azimuths spread over 8 localities were made. 62 The rose diagrams (Fig31) show distribution of dip azimuth at locality level and sector level. The arrow indicating vector mean ( v) and vector magnitude (L%). Vector mean ( v), were calculated by following vector simmition method of Curry (1956). The results are shown in Table No. V. VECTOR MEAN Vector mean ( v) is the most commonly used and accepted parameter dealing with the orientation data (Curry 1956; Potter and PettiJohn, 1963). Curry (1956) stated that the vector mean provides a unique value of central tendency, irrespective of choice of origin of measurements. The vector mean values determined for 4 localities ranges from 106 to 197 and at sector level is 165 . At sector B, the vector mean was determined for 4 localities and CO* the values ranges from 75 to 230 and at sector level xs 0 180 . VECTOR STRENGTH This parameter is necessary to determine the magnitude of the resultant of cos and sin components. Curry (1956) and many others indicate that 'L' is the vector strength or consistency ratio, provides some indication of dispersion. The vector strength (L%) was calculated at locality level and at sector level. At sector A, the vector strength ranges 63 Fig. 31. Map showing variations in flow direction from general flow direction. Rose diagram showing frequency distribution of cross stratification azimuths in 30° class interval in percent, Numbers within Circle represents Trench Number. Arrow indicates vector mean. 64 TABLE NO. V COMPUTATION OF VECTOR MEAN AND VECTOR MAGNITUDE OP CROSS-BEDDING AZIMUTH SECTOR UXAQTY UDCAU7Y LEVa SECTOR LEVEL NUfBER nV L IS^nV LIS^ (in degree) (in percent) (in degree) (in percent) 57 106 89.83 28.73 825 2 53 190 87.55 31.00 963 A 235 165 78.02 21 461 3 58 197 92.00 35.15 1255 « 67 127 82.81 34.75 1206 5 39 162 84.98 32.86 1080 6 41 Z30 90.24 28.38 806 B 180 140 53.0B 68 4630 9 46 75 82.00 35.00 1880 10 54 ICS 87.00 32.00 1053 n = Number of observations V = Vector mean L% = Vector magnitude 1 = Standard deviation 2 S = Variance of cross-stratification dip azimuths. 65 from 82.81 to 92 percent at locality level and is 78.02 percent at sector level. At sector B, the vector strength values ranges from 82 to 90 percent at locality level and 53.03 percent at sector level. VARIANCE The degree of scattering around the mean is measured quantitatively in order to define the population of vector azimuth. The variance (S) of foreset dip azimuth at the sector level varies from 461 to 4630 in the area under investigation. These values are the indication of the scattering of dip azimuth about the mean and are numerically equal to the square of standard deviation. The variance significantly shows large variance in the current direction. The variance values of cross stratification azimuths of Godavari delta sediment A 481, B 4636. Sector A is minimum value of 4000-6000 generally attributed to fluvial sequences (Potter and PettiJohn 1963), and Sector B value fall within the range and the inflated sector variance may be integration of the various flow-systems represented by regional components. This variation is due to variability in attitude of superimposed bed-forms within the channel fill of Godavari sediment. 66 INTERPERTATION Synthesis of the data reveals that the current direction obtained from the orientation data, by and large coincides with the present flow direction of the river. But it is not applicable for all over the area under investigation. However, Godavari river shows large variation in flow pattern from those indicated by the orientation data. The nature of the river system prevailing at the time of the deposition of that particular cross-stratified unit. The Godavari river being of the distributary channels of nature, did not flow constantly in the same direction for a long distance due to the presence of bars, developed in the earlier cycle of the deposition. The sediments deposited on the bank during floods show large variation in the current direction from the main flow. 67 CHAPTER VI CHAPTER VI DELTA MODEL The detailed study of the sedimentary structures and facies architecture of Godavari river delta showing various types of flow regimes. A depositional environment is a complex of physical, biological, chemical, tectonic and climatic conditions, prevailing at the time of deposition Shepard and Moore (1955). The first three of these attributes are of local character and determine the environment of depositional site. While tectonic setting and climatic conditions are broader controls which impress certain common character on sediments deposited in the basin under different local conditions and tie them into a consangeinous association. Seasonal variations control the deposition, so that at the time of high discharge the river transports more gravels than sand. The coarse clasts at the base represent deposition by lateral accriation. On other hand fine sediments represent vertical accriation on top of channel bars (Smith 1974, Cant 1978). During low discharge smaller thickness of fine clasts sediments suggest preservation and rapid shifting channel bars. In the present study, an attempt has been made to develop a depositional model for the river Godavari. Eight trenches were made on the river channels and two from overbank deposits. The trenches dug in the channels are characterized by coarsening 68 upward sequence (Fig.32). The block diagram shows generalised sequence from river channels to overbank deposits (Fig.33). The bottom of the trench shows parallel laminations of current ripples. The current ripples represent a supply of coarse sand in large amount and parallel laminations indicate fine grains and zero current velocity. Current ripples underlain by trough cross bedding, these large scale trough cross bedding are supposed to form in the upper part of low flow regime (Simon and Richardson, 1961). The formation of crossbedding is controlled by current velocity and flow characteristics and rate of sediment supply and infilling of scours by migrating dunes. Trough cross stratification, overlain by planar cross stratification (Fig.32), the sediments were migrated in the bar surface and slip on the avalanche face resulting in planar cross stratification Morison and Hein (1987). The planar cross stratification perhaps forms due to migration of bars. In turn the planar cross stratification overlain by pebbles bed in coarse sand laminations suggesting unstable high seasonal floods Morison and Hein (1987). Overbank deposits showing upward fining sequence, with small scale ripples overlain by climbing ripple laminations. Small scale ripples and climbing ripple laminations may have developed by current or wave action, 69 MASSIVE MUD CLIMBING RIPPLE LAMINATION SMALL RIPPLE BEDDING PARALLEL LAMtNATIONS PLANAR CROSS BEDDING TROUGH CROSS BEDDING CURRENT RIPPLES PARALLEL LAMINATIONS OLDER SEDIMENTS L FI6.( 32) GENERALIZED SEQUENCE OF 60DAVARI RIVER DELTA . 70 Fie,'. 33. Block diagram showing Bedforms ind stratifications of the Godavari Delta. 71 depositing sand, silt and clay with stack water. These climbing ripple laminations overlain by muddy massive unit, which indicate the slow moving conditions. The sedimentary structures and sediment size differ in the sequence developed in the channel and the overbank. Generally the channel deposits show coarsening upward cycle, where as the sequence developed an the overbank has fining upward sequence. 72 CHAPTER VII CHAPTER VII CONCLUSION The river Godavari is the greatest river of South India running from Triambak to Bay of Bengal (900 miles). It deposits vast quantity of sediments, resulting in formation of Godavari delta. Under the area of investigation, the river shows straight flow pattern carrying sediments of various size. Seven sedimentary facies have been recognised namely, trough cross bedded facies (St), planar cross bedded facies (Sp), ripple cross lamination facies (Sr), horizontal bedded facies (Sh), parallel lamination bedded facies (Fl), lenticular bedded facies (SI), and massive mud silt and clay facies (Fm). The cross-stratifications both planar and trough are most abundant facies. They are produced by the migration of sand ripples in the down stream with lateral growth of channel bars. The ripple drift cross laminations second in abundance and occur in two forms. One in which laminae are in phase and other in which laminae are in drift. Low current velocity and abundant supply of sediment is responsible for the formation of this facies. Whereas, the horizontal laminated facies developed in sands deposited in a upper flow regime. Apart from these facies, there are 73 other distorted facies i.e., parallel laminated facies developed in zero current velocity. Climbing ripples are post depositional and produced due to unequal loading. Massive muddy facies covers the large part of the deposits is regarded as post depositional structure. Lenticular sandy facies is another type of facies produced due to short lived current carrying sands. Towards the down stream of the distributary channels the mean size of sand decreases whereas sorting slightly increases, skewness changes from negative to positive, while kurtosis remains almost unchanged. On the basis of mineral composition, it is concluded that the provenance of the Godavari river sands consist chiefly of the precambrian khondalites, charnokites, and calc-granulites, and to a smaller extent of the Dharwars and the Gondwanas. The Deccan traps consist more than half of the drainage basin of the Godavari river, but there is no specific heavy mineral species present in the sands of Godavari river sediments studied, which points out to the Deccan trap provenance. All the samples of Godavari river sands the total heavy mineral content by weight is relatively high in the results presented in the foregoing paragraphs. The distribution of the dip azimuths of cross stratifications show variations in current direction from 74 general flow pattern due to development of a distributary channels. It is quite clear that there is a lateral and vertical variation in the sedimentary facies, texture and mineral composition of the deltaic sediments of the Godavari river investigated. 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