Indian Journal of Geo-Marine Sciences Vol. 42(3), June 2013, pp. 375-382 Depositional environment of sediments along the Cuddalore coast of Tamilnadu, India S.Viveganandan1, C.Lakshumanan1*, M.Sundararajan2*, S. Eswaramoorthi3 & Usha Natesan4 1 Centre for Remote Sensing, Bharathidasan University, Tiruchirappalli-620 023, India 2 National Institute for Interdisciplinary Science and Technology (CSIR), Thiruvananthapuram, 695 019, India 3 Department of Civil Engineering, Anna University of Technology, Thiruchirappalli-620 023, India 4 Centre for Environmental Studies, Anna University, Chennai- 600 025, India. [*E-mail: [email protected]/rajanmsundar77 @yahoo.com] Received 11 April 2011; revised 8 February 2012 Surficial sediments of beaches along the Cuddalore, central coast of Tamilnadu from Ponnaiyar estuarine to Thirumulaivasal were studied for their textural parameters namely Mean (Grain size) phi, Standard deviation, Skweness and Kurtosis and mineral percentages. Observed variation of energy conditions are controlled by the fluvial profile in the river channel. Textural analysis of medium sand shows the existence of comparatively high energy condition in the marine environment and low energy conditions in the fluvial zone. Linear Discriminant Function (LDF) analysis of the samples indicates a shallow marine environment origin for most of the samples and very few numbers of samples originated from fluvial environment. Heavy mineral content serves as an index for stratigraphic correlation of unfossilferrous strata. The lowest heavy mineral content indicates progradational activity and low energy wave conditions. These results show that reworked sediments, submerged during the Holocene marine transgression are being deposited on present day beaches by waves, currents and rivers in the study region. [Keywords: Beach sediments, Grain size, Depositional environment, India] Introduction In India, coastal regions are increasingly being used for placer sand mining, recreation, aquaculture, coral mining, and fishing. Earlier workers1-4 attempted the application of light mineral analysis in provenance studies. Anirudhan5 illustrated the petrography of light detrital minerals of Bharathapuzha to decipher the depositional history. Muthukrishnan6 studied light minerals from the Gadilam River in order to understand the maturity of quartz, orthoclase and microcline. The studies of light minerals from Vaippar and Gadilam River sediments concluded that they are influenced the continental block provenances7-8. The introduction of the Coastal Regulation Act and the Offshore Mining Bill for the exploitation of mineral deposits off the Indian coast has highlighted the importance of documenting coastal processes and sediment characteristics. The increasing demand for exploring and exploiting non-living coastal resources like placer deposits emphasises the need to compile more extensive inventories of these deposits that include sediment systematics such as grain size. Present study consists he documentation and the characteristics of grain size and mineral content from the Cuddalore coast to characterize the sediment source. Materials and Methods Study area The study area is located on the Cuddalore coast of Tamilnadu in Southern India and it is bordered on the east by Bay of Bengal. It lies Ponnaiyar estuarine in north and Thirumulaivasal in south and lies between11° 50’ to 11° 10’ N latitude and 79° 45’ to 79° 55’E longitude Fig. 1. The nearest major sediment Fig. 1Location map of the study area 376 INDIAN J. MAR. SCI., VOL. 42(3), JUNE 2013 source for this coastal segment is the Ponnaiyar, Gadilam, Uppanar Rivers in the north and Vellar and Coleroon River in the south. Sediment samples were collected from 18 locations of different landforms from Cuddalore beach and locations of samples were recorded carefully with GPS. Sediment samples were collected from 100-150 ft distance from water using spatula to a depth of 15cm. Distance between samples were used for 2-3 km parallel to the coast at the elevation of above 10ft. Sediment samples were stored in polythene bags. Samples were heated constant temperature of 60°C in a hot air oven to remove moisture. In order to ensure the uniformity of heavy mineral distribution, about 120 grams was removed by repeated coning and quartering method, while the remaining samples were kept for further reference. From the subsamples, 100 g was used for granulometry study and 20 g was used for heavy mineral separation. Then the samples were washed under mechanical stirring, with liberal amount of distilled water and decanted carefully to prevent losses. Process of washing and decantation was repeated until a clear water column was present. After decantation, the samples were kept for drying. The 30% by volume of H2O2 was added to the sample to remove the organic debris in the sediments. Sample was then washed with distilled water and dried. After drying it was weighed to measure the organic material losses. Same samples were treated with ~10% HCl to remove the calcareous materials present in the sediments. After proper washing and drying, sample was weighed to measure the carbonate losses. Dried samples were used for heavy mineral separation. For sieving, ASTM sieves from +10 to -230 mesh sizes (2 mm to 63µm) were used with 1/2 phi intervals9. Ro-tap sieve shaker was employed for separation with a 15 minutes shaking time for every sample. Sieved materials were weighed separately. Then the fractions were properly tabulated and the sands of the respective fractions were kept for further studies. Grain size parameters like Graphic Mean (Mz), Inclusive Graphic Standard Deviation (SD), Inclusive Graphic Skewness (Sk1) and Graphic Kurtosis (KG) were determined using the software package. Linear Discriminant Function (LDF) of Sahu10 was used for the multivariate analysis of the beach sediments. Separating funnel was used for heavy mineral separation with Bromoform of 2.89 specific gravity11. Separated heavy fraction was washed first with methyl alcohol and then with distilled water. Washed fractions were dried in a hot air oven (60°C), until the moisture was completely removed. Then the dried fractions were weighed and the values noted. Results and Discussion Mean Grain size Mean is the arithmetic average size of the sediment and is expected to be influenced by source of supply, transport and environment of deposition. The moment mean values are observed to be identical to the graphic mean data for the analysed samples, Folk and Ward9, observed that ‘the graphic mean values are twice as accurate an approximation as the moment means value. Coarsest sediments were found in the northern part of Cuddalore (stations 1 and 2) and southern part (stations 14, 15 and 16), the graphic mean size ranges from 0.6 to 0.94 Ø (Fig. 2). Because of the prevailing high wave energy environment, strong winnowing must have removed the fine sediments, leaving the coarser sediments. This is also evidenced by the erosive action of the waves. Varadachari12 reported high energy condition is also attributable to the presence of submarine canyons in the Pondicherry and Cuddalore regions. Chauhan13 also reported the coarser sediments at Cuddalore to be the result of erosion. In other areas (Stations 3 and 11), the mean size ranged from 1.03 to 1.78 Ø indicating the predominance of medium sands. Standard Deviation The sorting values for sample stations (1, 2, 5, 6, 7, 9, 10, 12, 13, 14, 15, 16, and 17) range from 0.42 to 0.70 indicated that the sediments are well sorted (0.35-0.5 range) to moderately well sorted (0.5-0.7range) (Fig. 3). This well sorted nature Fig. 2Mean grain size of Cuddalore beach sediments from north to south (station 1-18) Fig. 3Standard deviation of Cuddalore beach sediments (n = 18) VIVEGANANDAN et al: DEPOSITIONAL ENVIRONMENT OF SEDIMENTS ALONG THE CUDDALORE COAST (station 1, 15, 16 and 17) can be put down to the mixing of sediments brought by waves and currents, in addition to the input of palaeo-sediments from the major river systems (Ponnaiyar and Coleroon). Moderately sorted sands are predominant on the beaches (station 4, 8 and 18) of the east coasts of India14. Sorting values from 0.51 to 0.70 and 0.72 to 0.97 (Table 1) indicate that these sediments are moderately well (0.5-0.7 range) to moderately sorted (0.7-1.0 range). This is the result of the mixing of the sediments brought from the adjacent beach ridges. Standard deviation varies between 1.3 and 1.18, indicating that the sediments are poorly sorted (1.0-2.0 range). It is characterized by high energy wave conditions and mixed type of sediments. Folk and Ward9 observed that the medium to fine sediments are better sorted than very fine sediments. However our study shows that the medium grained sands are poorly sorted. This may be due to the influence of various modes of transport leading to poorly sorted sediments. During monsoon and cyclonic storms enormous quantities of suspended sediments are pushed from north to south. This may result in for the poor sorting of sediments in this area. Figures 4 and 5 shows the frequency weight percentage and cumulative weight percentage diagrams of the 18 sampled beach sediments. Frequency curve indicated symmetrical distribution for most of the stations. But the curve is showing very poor sorting and deficiently peaked kurtosis to the phi values in the case of stations 3 and 11. Cumulative weight of the beach sediments shows sigma distribution between the phi values of 0 to 2.5 in the case of stations 3 and 11 whereas the distribution is typically very poor. Bivariant 377 plot of mean vs standard deviation (Fig. 6) also shows that the sediments in both the stations are poorly sorted. Skewness The positively skewed distribution indicates a depositional tendency15. All the tested sediments are positively skewed suggesting the influence of fine sediments discharged by the rivers. River mouths are also marked by the growth of small sand bars. Stations from non-river point show positive Skewness Fig. 4Frequency weight percentage curves of Cuddalore beach sediments (n = 18) Fig. 5Cumulative weight percentage curves of Cuddalore beach sediments (n = 18) Table 1 Statistical analysis of Grain size distribution of Cuddalore beach sediments. S.No Mean 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 0.6 0.94 1.64 1.16 1.25 1.19 1.09 1.78 1.03 1.26 1.76 1.16 1.44 0.79 0.72 0.84 1.07 1.06 Standard deviation Skewness Kurtosis 0.49 0.55 1.3 0.97 0.7 0.51 0.58 0.72 0.52 0.66 1.18 0.51 0.54 0.6 0.48 0.42 0.48 0.77 0.18 0.49 0.13 0.1 0.18 0.14 0.13 0.2 0.14 0.08 0.22 0.14 0.45 0.15 0.13 0.3 0.15 0.36 1.15 1.38 0.74 1.29 1.01 1.12 1.31 1.02 1.3 0.87 1.03 1.18 1.3 0.73 1.12 1.13 1.13 2.52 Mean Coarse sand Coarse sand Medium sand Medium sand Medium sand Medium sand Medium sand Medium sand Medium sand Medium sand Medium sand Medium sand Medium sand Coarse sand Coarse sand Coarse sand Medium sand Medium sand Standard deviation Skewness Well sorted Fine skewed Moderately Well sorted Very fine skewed Poorly sorted Fine skewed Moderately sorted Fine skewed Fine skewed Moderately Well sorted Fine skewed Moderately Well sorted Fine skewed Moderately Well sorted Moderately sorted Fine skewed Fine skewed Moderately Well sorted Fine skewed Moderately Well sorted Poorly sorted Fine skewed Fine skewed Moderately Well sorted Moderately Well sorted Very fine skewed Moderately Well sorted Fine skewed Well sorted Fine skewed Well sorted Fine skewed Well sorted Fine skewed Moderately sorted Very fine skewed Kurtosis Leptokurtic Leptokurtic Platykurtic Leptokurtic Mesokurtic Leptokurtic Leptokurtic Mesokurtic Leptokurtic Platykurtic Mesokurtic Leptokurtic Leptokurtic Platykurtic Leptokurtic Leptokurtic Leptokurtic Very Leptokurtic 378 INDIAN J. MAR. SCI., VOL. 42(3), JUNE 2013 (Fig. 7). Positive value indicates an excessive supply of fine materials brought in by littoral currents. Rao16 reported the positive Skweness of the beach sediments of False Devi point in Andhra Pradesh to the excessive supply of fine sediments brought in by littoral current. In the present study mean size Vs Skewness plot (Fig. 8) indicates that, the severe contribution of supplying fine sediments from the offshore region except low current estuaries. Standard deviation Vs Mean plot (Fig. 9) shows most of the sediments are moderately well to moderately sorted. This sector has no fluvial influence except the two samples (stations 3 and 11) were poorly sorted. This plot clearly indicates these sediments are the influence of fluvial environment because the river input is more than the littoral current. Scatter plot of standard deviation Vs Skewness (Fig. 10) also helps to characterize these sediments. In the study area from north to southern region, all the samples have no fluvial influence except at the stations 3 and 11 but the station 4 is closer to the fluvial influence. Station 4 is nearer to the mouth of Uppanar River and based on the wave and seasonal influence play an important role. Fig. 6Scatter plot of Mean Vs Standard deviation for Cuddalore beach sediment Fig. 9Scatter plot of Standard deviation Vs Mean for Cuddalore beach sediment Kurtosis The graphic kurtosis is the qualitative measures of the part of sediments already sorted elsewhere in a high energy environment and later transported and modified such as beach, shallow marine and fluvial environment. Values of the graphic Kurtosis range between 0.73 and 2.52 (Fig. 11). Majority of the Fig. 7Skewness of Cuddalore beach sediments (n = 18) Fig. 10Scatter plot of Standard deviation Vs Skewness for Cuddalore beach sediment Fig. 8 Scatter plot of Mean Vs Skewness for Cuddalore beach sediment Fig. 11Kurtosis of Cuddalore beach sediments (n = 18) VIVEGANANDAN et al: DEPOSITIONAL ENVIRONMENT OF SEDIMENTS ALONG THE CUDDALORE COAST samples falls under leptokurtic nature of distribution. Very small number of samples falls under the platykurtic and mesokurtic nature but station 18 falls under the very leptokurtic nature. Variation in the kurtosis values is a reflection of the flow characteristics of the depending up on the medium, the dominance of medium size sands of leptokurtic nature reflecting the maturity of the sand. This may be due to the aggregation of sediment particle size by dense and the variations in the sorting values are likely due to continuous addition of medium/coarse materials in varying proportions. 4.5 Linear Discriminant Function analysis (LDF) According to the variations in the energy and fluidity factors seem to have excellent correlation with different processes and the environment of depositions17. Sahu’s 10 Linear Discriminant Function Analysis (LDF) of Y1 (Aeolien, Beach), Y2 (Beach, Shallow agitated water) and Y3 (Shallow marine, Fluvial) were used to decipher the process and environment of deposition. With reference to the Y1 and Y2 values, all the samples fall in beach process and ten samples fall in shallow agitated water and rest of them falls in Beach. Further the samples in Y3 indicate that they were of the combination of shallow marine and fluvial process (Table 2). Most of the samples fall in shallow marine process except those from the locations 3, 4 and 11. These samples located in the mouth of the river Uppanar and Vellar reflect the influence of a fluvial environment. The sediments discharged by the river Uppanar and Vellar must have been redeposited in this region by the wave action. It can be inferred that the sediments in the present day beaches must have been deposited in a shallow marine environment and marine deterioration must have led to the development of the present day shorelines. Minerals Beach is a temporary or short lived deposit on the shore. Most of the materials are sand and silt sized grains. The waves and tides have played a major role in the shaping of shoreline. Weight percentage of heavy minerals varies from 0.92 to 23.22% with an average of 5.6% (Fig. 12). Stations 11, 12, 15 and 17 show a relative high percentage of heavy minerals (Fig. 13). Heavy mineral percentage of sample at station 11, 12, 15, and 17 (9.24%, 10.52%, 6.41% and 23.22% respectively). This percentage is attributed to Fig. 12Heavy mineral distribution map of the study area Table 2Linear discriminate function values (Sahu 10) S.No Y1 Y2 Y3 Y1 379 Y2 Y3 1 1.95 49.70 -2.75 Beach Beach Shallow marine 2 1.04 68.99 -4.71 Beach Shallow agitated Shallow marine 3 2.43 152.76 -14.93 Beach Shallow agitated Fluvial 4 3.15 105.66 -8.33 Beach Shallow agitated Fluvial 5 0.12 73.71 -4.76 Beach Shallow agitated Shallow marine 6 -0.08 58.97 -2.57 Beach Beach Shallow marine 7 1.16 65.76 -3.20 Beach Shallow agitated Shallow marine 8 -1.67 84.42 -4.961 Beach Shallow agitated Shallow marine 9 1.08 60.48 -2.69 Beach Beach Shallow marine 10 -0.34 65.89 -3.80 Beach Shallow agitated Shallow marine 11 1.62 142.08 -12.72 Beach Shallow agitated Fluvial 12 0.20 59.61 -2.57 Beach Beach Shallow marine 13 -0.94 73.90 -4.28 Beach Shallow agitated Shallow marine 14 0.47 52.24 -3.62 Beach Beach Shallow marine 15 1.50 49.48 -2.39 Beach Beach Shallow marine 16 0.55 51.08 -2.71 Beach Beach Shallow marine 17 0.24 55.51 -2.39 Beach Beach Shallow marine 18 5.50 108.70 -6.53 Beach Shallow agitated Shallow marine Note: This table indicates all the samples in beach sediments and the depositional environment is mostly shallow marine 380 INDIAN J. MAR. SCI., VOL. 42(3), JUNE 2013 the intensive role of winnowing action of waves and currents. The higher percentage indicates that the light minerals are removed by winnowing of waves. Weight percentage of light mineral deposits varies from 76.78% to 99.08% (Fig. 14) with an average of 94.4% for the 18 sampled Cuddalore beach sediments. Relative higher percentages were recorded at the stations 5, 7, 9, 13, 14 & 16 (>98%). This higher percentage of light minerals indicates the progradational activity and low energy wave condition in the study area. Heavy minerals Sediment samples were used for microscopic study for the identification of heavy minerals. Only five estuarine stations such as Ponnaiyar, Gadilam, Uppanar, Vellar and Coleroon were selected and five different heavy minerals were identified but Ponnaiyar estuary has resulted two types of heavy minerals whereas, Vellar and Coleroon have resulted similar type of mineral. ferro and calcium magnesium- silicate minerals, such as amphiboles and pyroxenes in prominent amounts, and lesser amount of kyanite could indicate igneous and/or metamorphic sources11. Presence of pyroxenes reflects basic igneous rocks; and amphiboles, represents igneous and/or metamorphic rocks19-20 (Fig. 15). Kyanite Kyanite is a polymorph mineral that shares the same chemistry but a different crystal structure with another. It is an attractive mineral that has a near sapphire-like blue colour but also can be white, gray or green. Kyanite has a nearly unique characteristic in that it has a wide variation in hardness in same crystal face (Fig. 16a). The hardness of Kyanite is approximately 4.5 to 6.5 and specific gravity of 3.58. It is a refractory material and it has a high melting point, low thermal conductance and maintains its strength upto 1100°C. Hypersthene Pyroxene, Amphibole The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Amphiboles are minerals of either igneous or metamorphic origin; in the former case occurring as constituents (hornblende) of igneous rocks, such as granite, diorite, andesite and others. Calcium is sometimes a constituent of naturally occurring amphiboles18. The occurrence of Hypersthene is a relatively common mineral and is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Hypersthene is the intermediate member with around 50% iron and ferrosilite is the iron rich end member of the series. It is an orthopyroxene or a pyroxene with an orthorhombic symmetry (Fig. 16b). At high temperatures, its structure changes to a monoclinic symmetry and a clinopyroxene. Hypersthene has an ornamental variety. A weathered variety that has a sub metallic luster and a bronze like colour is called “bronzite”. It is sometimes used as an ornamental stone. It is a gray, brown colour mineral and hardness is approximately 5-6. The specific gravity of this mineral is approximately 3.4-3.9. Ilmenite Fig. 13Heavy mineral percentage of Cuddalore beach sediments (n = 18) Fig. 14Light mineral percentage of Cuddalore beach sediments (n = 18) Ilmenite is an economically important and black colour mineral. It is named for its place of discovery at Ilmen Lake in the Ilmen Mountain, Russia. It forms as a primary mineral in mafic igneous rocks. It also occurs in pegmatites and some metamorphic rocks as well as in the sedimentary rocks that are formed from the weathering and erosion of them (Fig. 16c). The hardness of ilmenite is 5-6 and its specific gravity is 4.5 -5. Fig. 15Mineral composition VIVEGANANDAN et al: DEPOSITIONAL ENVIRONMENT OF SEDIMENTS ALONG THE CUDDALORE COAST 381 Fig 16Different type of heavy minerals in Cuddalore estuaries: (a) Pyroxene ,Amphibole, Kyanite (Ponnaiyar estuary), (b) Pyroxene ,Amphibole, Hypersthene (Ponnaiyar estuary),(c) Pyroxene ,Amphibole, Ilemnite (Gadilam estuary), (d) Pyroxene ,Amphibole, Laterite (Uppanar estuary), (e) Pyroxene, Amphibole, Sillimanite (Vellar estuary), (f) Pyroxene ,Amphibole, Sillimanite (Coleroon estuary). Laterite Laterites are soil types rich in iron and aluminum, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock. Tropical weathering (laterization) is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils (Fig. 16d). Sillimanite Sillimanite is an alumino-silicate mineral. It is an orthorhombic with square cross sections and rounded. It is presented in white to gray, also brown, yellow, and yellow-green. A polymorph is a mineral that shares the same chemistry but a different crystal structure with another, or other minerals. Sillimanite is the rarest of the three trimorphs (Fig. 16e and f). The hardness is 7.5 in large crystals but more fibrous forms are softer and the specific gravity is approximately 3.2. Conclusion Most of the sediments are medium to coarser grained sand as beaches are steeply sloping and high wave energy conditions. The location 3, 4 and 11 under moderate sloping beach sediments are medium owing the fluvial discharge. Mixing of sediments under high and low energy conditions has affected the sorting of sediments. Beach processes have affected the sorting characteristics of the sediments. Skewness values indicates the depositional processes such as winnowing action of waves and currents and 382 INDIAN J. MAR. SCI., VOL. 42(3), JUNE 2013 decreasing energy of the transporting process in some of the places. This is endorsed by the development of sand bars at the mouth of the river point. Bivariant plots such as mean vs standard deviation, mean vs skewness, standard deviation vs mean and standard deviation vs skewness present an overlapping of the fluvial, marine and beach environments in the beach samples of the study area. LDF result shows that most of the sediments are deposited under shallow marine environment by beach and fluvial processes due to near shore agitating turbidity action of water. Landforms help to infer various stages of the study region. Nature of the concentration of heavy mineral is suggestive of the influence of higher wave energy in middle and southern part of the study area. 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