INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 6, No 5, Copyright by the authors - Licensee IPA- Under Creative Commons license 3.

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1 INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 6, No 5, 2016 Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN Vertical sequences of Lithofacies in point bar and natural levee deposits, Tons River, Allahabad, U.P., India. Department of Earth & Planetary Sciences, University of Allahabad, Allahabad siddharthasankardas.alld@gmail.com doi: /ijes.6070 ABSTRACT The recent sediment of Tons River at Allahabad, Uttar Pradesh is studied for lithofacies variations in vertical sections of sixteen point-bar and two natural levee deposits. Altogether, seven lithofacies, namely Gcs, St, Sp1, Sp2, Sr, Sh and Fm: One gravel, five sand and one mud sub-lithofacies have been identified. The point-bar deposits exhibits lithofacies succession of Gcs, St, Sp2, Sp1, Sr, Sh and Fm; whereas levee deposits exhibit only Sp2, Sh and Fm. The Fm lithofacies, muddy deposits often show desiccation cracks. Gcs and St are characteristic lithofacies of point-bar deposits only. Facies Gcs is a product of deposition from steady traction flows, formed by foreset deposition along an avalanche face at the downstream end of a bedform (gravel transported as bedload sheets). Lithofacies St is formed by the migration of 3D dunes and or infill of minor channels or depressions. The facies Sp is connected with foresets from avalanche faces of advancing 2-D sand dunes during lower flow regime. Sand is transported up by the flank of the bed forms by traction and intermittent suspension and deposited at the crest, where the bed shear stress drops at the point of flow separation. The low angle planar foreset (Sp1) suggests transitional bedforms between high and lower flow regime. The facies Sr is a product of deposition from waning traction flows in the lower flow regime. Lithofacies Sh is the product of deposition of sand from traction flows near the transition phase between lower and upper flow regime. The facies Fm is interpreted as a product of deposition at low energy condition (quiet water) from suspension during waning flow conditions. The vertical successions studied in point-bar and levee deposits are in conformity with the standard models of fluvial deposits. The sediment grain-size distribution showed systematic downstream fining and development of log-normality. The study also showed that the sediment of Tons River was transported by rolling and suspension currents. Keywords: Lithofacies, point-bar, natural levee, tons river, sand dune, grain-size. 1. Introduction In fluvial environments, channel bars, point-bars and natural levee (overbank) are the main places of sediment deposition. Sediment characteristics of some channel bar deposits in modern sediments have been studied by many authors (Doeglas, 1962; Coleman, 1969; Tiwari, et al., 2004). The bedding characteristics in the point-bar and levee deposits of Gomti River are studied by Singh (1977). Singh and Kumar (1974) studied the occurrences of sedimentary structures in vertical profile of the Ganga River sediments. Tiwari and Gaur (1991) studied the structure and lithofacies sequences in point-bar deposits of Yamuna River. Tons river (locally known as Tamas), a tributary to River Ganges originates from the Vindhyan Plateau near Maihar, M.P. The confluence of this river with the Ganges located at Sirsa near Allahabad, U.P. The Tons River dominantly flows across Vindhyan Supergroup, later a small course on the Indo-Gangetic plain. About 85 km long segment of the Tons River Received on September 2015 Published on March

2 covering dominantly Allahabad district of U.P. and small parts of Rewa district, Madhya Pradesh (Topographic sheet Nos. 63G/12, 63 G/16, 63K/3 and 63K/4,) was studied for the present work (Figure 1). This research work is the results of the study carried out on the point-bar and natural levee deposits of Tons River with an objective to study the various lithofacies sequences in vertical successions. Figure1: Map of study area showing location of the vertical sections.(courtesy Google earth). 2. Methodology The various lithofacies of point-bar and natural levee deposit were studied in the field by making trenches (size about 1.5m long and 0.5m wide) made parallel to the flow (longitudinal section). The physical parameters (like structure, texture, colour, thickness), grain-size, sedimentary structures and nature of contact of the various lithofacies were carefully noted to establish the vertical succession (Figure 2a,b and c). The lithologs were prepared giving their characteristic features (Fig 3). In all, sixteen vertical sections were studied in point bar and two vertical sections in natural levee deposits. The sediment samples were taken from the various lithofacies by making vertical grooving an area o f 5cm wide and 5cm deep all along the individual unit. A total of fifty-four representative sandy samples were studied for grain-size analysis. The results of sieving were plotted graphically (cumulative frequency vs phi grain-size in probability scale) (Figure 4) and various statistical parameters (mean size, standard deviation, skewness and kurtosis) are calculated graphically using Folk and Ward formulae (1957). The results are given in Table 1. The various statistical parameters are also plotted against various facies to classify mean size, sorting, skewness and kurtosis of grain-size distribution (Figure 5). The coarsest one percentile grain size (C) and median grain size (M) of samples were plotted on a log-log paper (Passega, 1957) (Figure 6). Their studies proved helpful to delineate the character of deposition. 3. Lithofacies analysis A lithofacies is a sedimentary unit consisting of distinct lithology, composition, grain-size and sedimentary structures. The lithofacies associations are characteristic of particular depositional environments. Lithofacies in this work have been identified following the 747

3 classification of Miall (1978, 1996). Here, the lithofacies code consists of two parts, a capital letter for modal grain size (G for gravel, S for sand and F for fines) and a lower case letter or letters chosen as a mnemonic of a distinctive texture or structure of each lithofacies. Seven lithofacies have been identified in this area and described below. Figure 2: a) deposit showing Sp2, Sp1, Sh and Fm lithofacies, b) deposit showing Gcs, Sp2 and Fm lithofacies. c) Levee deposit showing Sp2, Sh and Fm lithofacies. 3.1 Gravel lithofacies (G) The facies is formed by planar cross-stratified gravel or sandy gravel (Gcs). This facies only encountered at two locations. Beds are stacked upon one another into bedsets (Figure 2b ). An upward reduction of both bed thickness and grain size can be followed in such stacked bedsets. Gravels are usually clast supported in lower parts of the beds in contrast to matrix supported upper parts. The upward reduction of the gravel content and an increase of the content of sand were observed. The inclination of cross-strata is generally varies between The gravels are dominantly made up of broken calcareous nodules. The diameter of the maximum clast varies in individual outcrops between 1 and 12 cm. The largest pebbles usually were located along the base of the bed. 3.2 Sand lithofacies (S) The sandy lithofacies are dominant lithofacies of the logged profiles. Based on the dominant primary sedimentary structures and grain-size, four distinct sandy sub-lithofacies (Sp, St, Sh and Sr) have been recognised. Sandy lithofacies in fluvial system results from the transport of sand by traction current, as bed load and in intermittent suspension. Sublithofacies Sp (Planar cross bedded medium to fine sand): This facies is represented by planar cross-stratified sands and forms dominant lithofacies of logged profiles. Based on the inclination angle of the foreset laminae this sub- lithofacies is further divided into two subfacies: Sp1 sub-facies, with foreset inclination less than 15 0 (Fig 2a) and Sp2 sub-facies, with foreset inclination more than 15 0 (Figure 2b). The thickness of the beds varies between 12 and 20 cm. Sands are mostly medium to fine grained, and generally quite well sorted. The soles are usually flat, but the character of upper bed boundary varies, i.e. flat, erosive, undulatory and inclined top were all observed. Both, the angular and tangential contacts of 748

4 cross-beds can be observed in sections. The facies was recognized in both the point- bars and natural levee deposit. Figure 3: Vertical profiles of point-bar and Levee deposits. Sublithofacies St (Trough cross bedded coarse to fine sand): The facies is represented by trough-cross-stratified sand and the thickness of the individual sets varies between 10 and 20cm. Beds have usually lenticular or channel like shapes. The base is usually erosive, rarely convex upward. The upper bed boundary is erosive in nature. The sand is dominantly medium-grained, rarely fine grained. The facies only found in point bar deposits. Sublithofacies Sr (Ripple cross laminated medium sand): The facies is represented by ripple cross-stratified sand and found only in two studied sections of point-bar. The sub-facies is overlying planar cross-stratified sand (Sp) facies. Sublithofacies Sh (Horizontally laminated fine to very fine sand): The facies horizontally laminated medium to very fine sand (Figure 2a and c). The sub-facies is found in both the 749

5 sections, point-bar and levee deposits. The bedding planes of the subfacies are often characterized by distinct colour banding imparted mainly by the concentration of heavy minerals. 3.3 Mud lithofacies Among the mud-lithofacies only one facies Fm, i.e massive mud was recognized in point-bar and levee deposits, often show desiccation cracks. Sublithofacies Fm (Massive mud): This mud sub-lithofacies dominantly consisting of silt and clay with the thickness of the beds laterally varying between 3 and 15cm. This facies is exposed at the top of sequences, almost at every point bar and levee deposits (Figure 3). The base is very irregular with concave or undulated shape. The top is typically sharp and marked by desiccation cracks. The mud is light grey to whitish grey, light brown and occasionally bluish grey coloured. 3.4 Grain-size analysis In the interpretation of grain-size distributions the classical sedimentological concept has been considered. According to that, the cumulative curves consist of several line segments, each segment symbolising categories of particles (populations) (Visher, 1969) moved by different modes of transport. In the fluvial sedimentology, the most typical cumulative curves are those consisting of three line segments, with the middle segment representing particles transported by saltation, the lower segment representing particles transported by traction (sliding or rolling) and the upper segment representing fine particles transported by means of suspension. In the Tons River, curves consisting of three line segments (Figure 4) are very frequent, suggesting the existence in the same kind of particles transported through traction, saltation or suspension or the combination of sediment sequences deposited in different hydrodynamic conditions. The grain-size distribution shows that dominantly sediment samples are made up of fine sand consisting of various facies (Figure 5). The sediments are dominantly moderately to well sorted and near symmetrical to fine skewed. Sediments are dominantly mesokurtic to leptokutic. The grain-size plots show there is gradual increase in saltation and suspension load over bed load in downstream direction of river flow (F igure 4). However, at three locations (9, 13 and 14) there is strong bed load transportation along with other modes of transportation of sediments (Figure 4). The CM pattern is an important plot used in sedimentology for the analysis of sedimentary environment (Passega, 1957, 1964). The CM Pattern of the sedimentary environment are means of analyzing transportation mechanism, depositional environment with respect to size, range and energy level of transpiration and also is determining the processes and characteristic agents that are responsible for the formation of clastic deposits. In the present study, CM pattern was made following Passega (1964). The phi values of 1 st and 50 th percentile were converted to microns to plot on CM diagram (Figure 6). The CM plot at the present study shows that most of the sediment samples fall in the intermediate position between graded suspension and rolling-suspension region, exhibits that the Tons River sediments were underwent the rolling and suspension current, which are the prime factors for transportation. 750

6 Figure 4: Cumulative weight frequency vs. grain-size plots (in probability scale). Figure 5: Classification of grain-size data vs. lithofacies in point-bar and levee deposits. 751

7 4. Discussion Lithofacies sequences in vertical sections of point-bar and levee deposits of Tons River are very useful in deciphering depositional conditions. The grain-size data are also helpful to predict conditions of sediment transportation. The facies Gcs is a product of deposition from steady traction flows, formed by foreset deposition along an avalanche face at the downstream end of a bedform (Kostic and Aigner, 2007). This facies can be classified as medium scale cross-stratification (Lunt et al., 2004). That is formed by straight-crested dunes and represents the most common internal structure of bars and channel fills. The stratification defined by contrasting grain sizes with vertical reduction of the grain size may reflect changing water stages over the flood cycles, temporal variations in flow strength (Ramos and Sopeńa, 1983; Rust, 1984), clast segregation over the surface of the bar (Steel and Thompson, 1983), or migration of smaller bed forms over dune/bar crests (Rust, 1984; Lunt et al., 2004). The low-angle stratification and lithofacies assemblages could suggest that the gravel was transported partly as bedload sheets (Hein and Walker, 1977). The mean set thickness is related to the mean height of formative dunes. Cross sets that are m thick typically would be formed by dunes with mean heights between 0.3 and 1.2 m.(lunt et al., 2004). The lithofacies although characteristic of upper reaches of river, but locally presence of Quaternary calcareous nodule bearing horizon and its erosion caused its development in the lower reach of river. The lithofacies St is interpreted as a product of deposition from traction flows during lower flow regime. It can be connected with the migration of 3D dunes, infill of minor channels or depressions (cut and fill). Figure 6: CM plot of grain-size data. The lithofacies Sp is connected with foresets from avalanche faces of advancing 2-D sand dunes during lower flow regime. Sand is transported up by the flank of the bed forms by traction and intermittent suspension and deposited at the crest, where the bed shear stress drops at the point of flow separation (Mial, 1996). The low angle planar foreset suggests transitional bedsforms between high and lower flow regime (Bhattacharya and Chakraborty, 2000). The facies Sr is a product of deposition from waning traction flo ws in the lower flow regime. Ripples form during low-flow stage or during floods in areas of slow-moving water. 752

8 Small-scale cross-strata are generally associated with the deposition in channels (final stages of the minor channel infilling), bar-tails, troughs and crests of dunes (Lunt et al., 2004). The lithofacies Sh is the product of deposition of sand from traction flows near the transition phase between lower and upper flow regime. This phase is very stable in fine to medium grained sand at velocities of around 1m/s and water depth of m (Collinson and Thompson, 1982; Tiwari et al, 2004). The lithofacies Fm is interpreted as a product of deposition at low energy (quiet water) from suspension during waning flow conditions. The grain-size distribution shows that dominantly sediment samples are made up of fine sand consisting of various facies. The sediments are dominantly moderately to well sorted, near symmetrical to fine skewed and mesokurtic to leptokutic. The grain-size plots show there is gradual increase in saltation and suspension load over bed load (development of log-normal grain-size distribution) in downstream direction of river flow. Sengupta et al (1999) also reported identical phenomenon from the Usri and Dwarekeswar rivers. However, at three locations (9, 13 and 14) there is strong bed load transportation along with other modes of transportation of sediments. In those locations the river has locally cut a Quaternary calcareous nodule bearing horizon, which provided gravel sized particles to the Tons river sediment. With the distance of transport, the coarser and finer particles of sediments are chopped off. The coarser particles are buried below the advancing bedforms/dunes on their lee sides. The finer particles are transported further downstream. Thus, the finer admixture giving rise to fining upward sequence, which overlies coarser fractions (Purkait, 2006). The study also shows that most of the sediment samples fall in the intermediate position between graded suspension and rolling-suspension, exhibits that the Tons River sediments were underwent rolling and suspension current, which are the prime factors for sediment transportation. Table 1: Variation of grain-size parameters in vertical sections of the study area. Location Geomorphi Lithofacie Mean Std.Dev. Skewness Kurtosis c unit s Size (ϕ) (ϕ) (SKI) (KGI) L-1 Sh N25 3ʹ7. St ʹʹ Sr E81 39ʹ Sp ʹʹ Sh L-2 N25 2ʹ4. 1ʹʹ E81 45ʹ 10ʹʹ L-3 N25 3ʹ5 5.6ʹʹ E81 47ʹ 38.1ʹʹ Sh Sr Sp Sh Sp L-4 N25 8ʹ3 3.1ʹʹ E81 49ʹ Sh Sp Sh

9 22.2ʹʹ L-6 N25 10ʹ 38ʹʹ E81 56ʹ 8.7ʹʹ L-7 N25 9ʹ4 8.9ʹʹ E81 58ʹ 18.6ʹʹ L-8 N25 9ʹ2 5.5ʹʹ E81 59ʹ 51.6ʹʹ L-9 (N ,E ) L-10 (N , E ) L-11 (N ,E ) L-12 (N , E ) L-13 (N ,E ) L-14 (N , E St Sp Sh Sp Sh St Sp Sh Sp Sp St Contd. Sp Gcs Not done Gcs Not done Gcs Not done Sp Sp Sp Sp Sp Sh Sp Sp Sp Sh Sp Sh Sp St Sh Sp Gcs Not done Sp St Sp Sp Gcs Not done Sp

10 L-15 (N ,E L-16 (N ,E ) L-17 (N , E ) L-5 N25 11ʹ13.2ʹʹ E81 56ʹ24.6ʹʹ L-18 N / //, E / 38.3 // Sh Sp Sp Sp Sp Natural levee Natural levee Sh Sp Sh Conclusion The lithofacies sequences in vertical sections of point-bar and levee deposits of Tons River are very useful in deciphering depositional conditions. The various lithofacies sequences found in the vertical succession of point-bar deposit are Gcs, St, Sp2, Sp1, Sr, Sh and Fm. Only three lithofacies, Sp2, Sh and Fm are found in levee deposits. The gravel bearing facies at the lower reaches of Tons River is typically developed due to presence and erosion of Quaternary calcareous nodule bearing horizon. The other facies are in conformity with the typical fluvial point-bar and levee deposits. The sediment grain-size distribution shows systematic downstream fining and development of log-normality. The study also showed that the sediment of Tons River fall in the category between graded suspension and rollingsuspension; and were transported by rolling and suspension current. Acknowledgement Author is thankful to Mr Satyendra Verma and Atul Singh for their support during field work and collection of samples. Ms Priti Rai helped during processing of grain-size analysis 6. References 1. Bhattacharya A., and Chakraborty C., (2000), Analysis of sedimentary successions: A field manual. Oxford & IBH Publ., New Delhi, p Coleman J. M., 1969, Brahmaputra river: channel processes and sedimentation, Sedimentary Geology, 3, pp

11 3. Collinson J.D., and Thompson D.B., 1982, Sedimentary structures, George Allen and Unwin Ltd., London, p Doeglas D.J., 1962, The structure of sedimentary deposits of braided rivers, Sedimentology, 1, pp Folk R.L., and Ward W., (1957), Brazos river bar: A study in the significance of grains-size parameters. Journal Sedimentary Petrology, 27, pp Hein F.J., and Walker R.G., (1977), Bar evolution and development of stratification in the gravelly, braided, Kicking Horse River, British Columbia, Canadian Journal of Earth Sciences, 14, pp Kostic B., and Aigner T., (2007), Sedimentary architecture and D ground-penetrating radar analysis of gravelly meandering river deposits (Neckar Valley, SW Germany). Sedimentology, 54, pp Lunt I.A., Bridge J.S. and Tye R.S., (2004), A quantitative threedimensional depositional model of gravelly braided rivers. Sedimentology, 51, pp Miall A.D., (1996), The Geology of Fluvial Deposits. Springer Verlag, Berlin, p Miall A.D., 1978, A review of the Braided river depositional environment. Earth Science Reviews, 13, pp Passega R., (1957), Texture as a characteristic of clastic deposition. American Association Petroleum Geology, 41, pp Passega R., (1964), Grain size representation by CM patterns as a geological tool. Journal Sedimentary Petrology, 34, pp Purkait B., 2006, Grain-size distribution patterns of a point bar system in the Usri River, India. Earth Surface Processes and Landforms, 31, pp Ramos A. and Sopeńa A., (1983), Gravel bars in low sinuosity streams (Permian and Triassic, central Spain), IAS Special Publication, 6, pp Rust B.R., (1984), Proximal braidplain deposits in the Middle Devonian Malbaie Formation of Eastern Gaspé, Quebec, Canada. Sedimentology, 31, pp Sengupta S.,., and Maji A., (1999), Sediment transportation and sorting processes in streams. Proceedings Indian National Science Academy, 65/A, pp Singh I.B. and Kumar S., (1974), Mega and giant ripples in the Ganga, Yamuna and Son river, U.P., India, Sedimentary Geology, 12, pp Singh I.B., (1977), Bedding structures in a channel sandbar of the Ganga River near Allahabad, U.P., India, Journal Sedimentary Petrology, 47, pp

12 19. Tiwari G.S., Tiwrai R.N. and Singh K.N., (2004), Vertical succession of channel bar, point-bar and natural levee deposits, Ganga and Yamuna river, Allahabad, U.P., Journal Geological Society of India, 64, pp Tiwari R.C. and Gour R.P., (1991), Structures and sequences in fine grained point bars of Yamuna river near, Etawah, U.P., Journal Geological Society of India, 38, pp Visher G.S., (1969), Grain size distributions and depositional processes. Journal Sedimentary Petrology, 39, pp