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Heavy mineral distribution and geochemical studies of coastal sediments between Besant Nagar and Marakkanam, Tamil Nadu, India
M. Suresh Gandhi*, M. Raja
Department of Geology, University of Madras, Guindy Campus, Chennai 600 025, India
ARTICLE INFO
ABSTRACT
Article history: Received 11 February 2014 Received in revised form 3 June 2014 Accepted 5 June 2014 Available online xxx
Keywords:
Heavy minerals
Geochemistry
Coastal sediments
Besant Nagar and Marakkanam
Tamil Nadu
The main objectives of the present study are to understand the heavy mineral distribution, trace elemental distribution and to study the variation, if any, between the grain size and trace elemental distribution within the beach. Totally 20 stations have been collected and weight percentage of heavy minerals are identified. In the present study area most of the sands are fine and medium grained, indicates beach environment and most of the grains are positively skewed. The study area contained a high percentage of orthopyroxene (hy-persthene) and garnet, rounded and broken zircons inferred to have been derived from charnockites and granulite gneiss of the study area. Overall from the geochemistry studies, it is observed that the Ni and Cr are more dominant and higher concentration in Panayar (station no. 2), Mahabalipuram (station no. 6), Kalpakkam (Station no. 7) and Perunthuravu (station no. 8). The present study has clearly indicated the multiple roles of tectonically controlled coastal blocks and their geomorphological influence in redistributing the sediments with favourable NE—SW configuration and wave energy conditions must have contributed to the formation of heavy minerals in a particular zone.
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1. Introduction
A placer deposit is the result of flowing water, particularly streams and rivers, causing an accumulation of mechanically segregated are minerals. The erosion of weathered rocks and
minerals results in the concentration of the more resistant and higher specific gravity (density) minerals (2.89). Placer deposits can be broadly classified on the basis of mode of origin and transportation into eluvial, deluvial, proluvial, alluvial (sub divided into bar, channel fill, valley delta and bench or terrace placers) lateral (subdivided into lacustrine, beach,
* Corresponding author. Tel.: +91 09443806534 (mobile); fax: +91 04422202789.
E-mail addresses: msureshgandhi@gmail.com, surgan@yahoo.co.uk (M. Suresh Gandhi), raja3geo@gmail.com (M. Raja). Peer review under responsibility of The Egyptian Society of Radiation Sciences and Applications
http://dx.doi.org/10.1016/j.jrras.2014.06.002
1687-8507/Copyright © 2014, The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. All rights reserved.
marine beach, and offshore placers) glacial (subdivided into moraine and fluvioglacial) and aeolian placers. India endowed with a coastline of over 7500 km, hosts some of the largest and richest shoreline placers. The beach and dune sands in India contain heavy minerals like ilmenite, rutile, garnet, zircon, monazite, sillimanite (Angusamy, Loveson, & Rajamanickam, 2004; Angusamy, Dajkumar Sahayam, Suresh Gandhi, & Rajamanickam, 2005; Angusamy & Rajamanickam, 2000; Behera, 2003; Ramasamy & Karikalan, 2010; Suresh Gandhi, Vetrimurugan, Angusamy, & Rajamanickam, 2007). Sources of Monazite beds of Orissa beach placer were studied by Rao and Misra (2009). Studies on the beach and dune heavy mineral deposits by close-grid sampling in the 508 km long coastal stretch of central and southern Tamil Nadu, reveals a high concentration of heavy minerals, most commonly from the surface down to a depth of several metres (Mohan & Rajamanickam, 2001). The present investigation was thus undertaken to fill this information gap.
1.1. Study area
The present study area, Besant Nagar to Alliyakuppam (near Marakkanam) is located south of Chennai (Fig. 1) and it falls in the survey of India toposheets 66 D/2 prepared in the scale of 1:50,000. The various geomorphic landforms like the beach, strandlines, sand dunes, alluvial plain, chennier, paleo lagoon, salt marshes, mudflats, flood plain, paleo-channel, salt pan, lagoons have been noticed nearby regions in the study area. The geographical position of the coast makes the region to experience the northeast monsoon between October and February and the southwest monsoon from May to September.
1.2. Methodology
A total of 10 sediment stations and 1 core station at Maha-balipuram were collected from Besant Nagar to
Fig. 1 - Location map of the study area.
(Aliyakuppam) Marakkanam beach. The core samples, were collected using a handheld PVC pipe upto 1.0 m depth of the dry, sandy deposits and subsampled into 10 cm and totally 20 stations were analyzed. In the lab, the sediment stations were dried in an oven at 60 °C to remove the moisture. Sieving was carried out in ASTM at V 4 interval. Using graphic (Folk & Ward, 1957) and moment methods (Friedman, 1961, 1967, 1979) the weight percentage data of 20 stations were processed in personal computer by using the modified programme of Schlee and Webster's (1967) procedure. Grain Size distribution and statistics package for the analysis of un-consolidated sediments by sieving or laser Granulometer developed by Blott and Pye (2001). From the mounted slides the individual (>300 grains) minerals were counted by using the line method described by Galehouse (1969). Various diagnostic properties of heavy minerals provided in the Milner (1962), Rothwell (1989), are utilized for easier identification.
1.2.1. Procedure for trace elements
For total digestion the geochemical analytical procedure suggested by (Tessier, Campbell, & Bisson, 1979) were followed. The HF-HClO4 was preferred because the sediments consist essentially of detrital silicate minerals, resistant sulfides and small quantity of refractory material. Treatment with HF-HCLO4 reagent results in complete dissolution. For total or residual trace metal analysis, the solid was digested with a 5:1 mixture of hydrofluoric and perchloric acids. For a 1 g (dry weight) station, the sediment was first digested in a Teflon beakers with a solution of concentrated HClO4 (2 ml) and HF (10 ml) to near dryness; subsequently a second addition of HClO4 (1 ml) and HF (10 ml) was made and again the mixture was evaporated to near dryness. Finally, HClO4 (1 ml) alone was added and the station was evaporated until the appearance of white fumes. The residue was dissolved in 12 N HCl and diluted to 25 ml. The solution was finally analyzed for total Fe, Mn, Cr, Cu, Ni, Co, Pb, and Zn on a Perkin Elmer AA 700 AAS equipped with a deuterium background corrector (source: Department of Applied Geology, University of Madras).
2. Result and discussion
2.1. Coastal geomorphology
The various geomorphic landforms like beach, strandlines, sand dunes, alluvial plain, chennier, paleo lagoon, salt marshes, mudflats, flood plain, paleo-channel, salt pan, lagoons have been noticed nearby regions in the study area. The mean significant wave height for this area is 0.39-1.66 (m). Tidal value for the entire study area coast is more or less equal to 1.2 m with lowest value as 0.1 and highest is 1.4 is recorded. Generally, the study area is influenced by the southwest and northeast monsoons. The climate in the study area is generally uniform and is influenced by the adjoining sea. During summer, the land temperature goes up to a maximum of 45 °C. The area experiences two phases of rainfall one during the southwest monsoon (June to September) as occasional showers and the second phase
during the northeast monsoon (October to December) when cyclones normally occur almost every year causing heavy downpour. The total annual rainfall varies between 1100 and 1250 mm, of which the northeast monsoon contributes about 50-60% and the southwest monsoon contributes about 30-40%. The coolest month is January with an average temperature of 25 °C and the hottest month is May with an average temperature of 37 °C.
2.2. Oceanographic parameters
The Chennai to Mahabalipuram coast with an orientation of 15° to the north and on the northern side, at a distance of ca. 100 km, the coastline has (1) a natural lake known as 'Pulicat Lake', and (2) widespread shoals in the nearshore region. The Chennai coast south of the above two exquisite features includes an inlet for a backwater, popularly known as 'Ennore creek'. The seabed in the region had a gentle slope of 1:100 prior to the implementation of short-term protective measures and the introduction of a rubble seawall along the coast has caused a considerable change in the seabed profile more specifically an increase in water depth along the seawall.
The geographical position of the coast makes the region to experience the northeast monsoon between October and February and the southwest monsoon from May to September. The wind and wave conditions that prevail in deep water during the monsoons are summarized below.
2.2.1. Northeast monsoon
Wind direction: 49-87°, relative to the North.
Wind speed: 5.8-7.5 m/s
Wave height: 2.5-3 m.
Wave direction: ca. 60° relative to the North
2.2.2. Southwest monsoon
Wind direction: 153-263° relative to the North. Wind speed: 2-12 m/s Wave height: 2-2.5 m.
Wave direction: about 135° relative to the North.
It indicates a maximum wave height of 2.5 m with a wave period of 6 s during the southeast monsoon in the study region. These values are 3 m and 10 s, respectively, during the northeast monsoon.
2.2.3. Tides
Tides at Besant Nagar to Mahabalipuram are semi-diurnal with a maximum tidal range in the order of 1.4 m. Characteristics of the tide, observed by the Chennai Port Trust suggested the following:
Highest High Water (H.H.W.) 1.50 m Mean High Water Spring (M.H.W.S.) 1.10 m Mean High Water Neap (M.H.W.N.) 0.80 m Mean Sea Level (M.S.L.) 0.54 m Mean Low Water Neap (M.L.W.N.) 0.40 m Mean Low Water Spring (M.L.W.S.) 0.10 m
2.3. Grain size analysis
In the present study, an endeavour has been made to make use of the grain size characteristics of sediments collected from different part of the environment that are subjected to various degrees of erosion, transportation and deposition mechanisms. The result of the grain size parameters of the graphic method (Folk & Ward, 1957) such as median, mean, standard deviation, skewness and kurtosis has been calculated (Table 1).
2.4. Frequency curves
Mode is the most frequently occurring particle diameter. The
study region from Besant Nagar beach to Marakkanam shows,
medium sand and fine sand in nature. In Besant Nagar to Panayur sector, mean value ranges from 2.12 4 to 2.65 4 indicating a prominent distribution of fine sand in this zone. The mean values demonstrate a gradational increase in the remaining region of this zone. The frequency pattern point towards the presence of unimodal distribution having peaked at 2.75 4. Mostly medium grained are dominated in this region. The medium sediments indicate the depositional environments either in the suspension, it can be transported by longshore current.
In the Mahabalipuram core, up to 10 cm depth it shows a bimodal pattern, whereas from 10 to 30 cm depths it shows a unimodal pattern. From 30 to 80 cm it shows bimodal distribution and up to 1 m depth it is unimodal in nature. It shows an alternate source of deposition. The anthropogenic
Station no Textural Moment method (Graphic method) Folk & Ward method
parameters Geometric Logarithmic Geometric Logarithmic Description
mm f mm f
1 Mean 212.9 2.063 238.6 2.067 Fine sand
Sorting (s) 2.307 0.705 1.605 0.683 Moderately well sorted
Skewness (Sk) -4.439 0.055 -0.030 0.030 Symmetrical
Kurtosis (K) 28.93 3.890 1.285 1.285 Leptokurtic
2 Mean 244.6 1.782 295.6 1.758 Medium sand
Sorting (s) 2.650 0.665 1.583 0.663 Moderately well sorted
Skewness (Sk) -4.467 0.172 -0.067 0.067 Symmetrical
Kurtosis (K) 25.49 3.771 1.143 1.143 Leptokurtic
3 Mean 247.3 1.977 240.6 2.055 Fine sand
Sorting (s) 1.788 0.689 1.711 0.775 Moderately sorted
Skewness (Sk) -3.560 0.589 -0.310 0.310 Very fine skewed
Kurtosis (K) 32.13 2.793 1.126 1.126 Leptokurtic
4 Mean 166.2 1.777 283.3 1.819 Medium sand
Sorting (s) 4.806 0.763 1.661 0.732 Moderately sorted
Skewness (Sk) -2.740 -0.760 0.240 -0.240 Coarse skewed
Kurtosis (K) 9.218 3.196 1.067 1.067 Mesokurtic
5 Mean 228.4 1.989 252.3 1.987 Medium sand
Sorting (s) 2.166 0.646 1.565 0.646 Moderately well sorted
Skewness (Sk) -4.860 -0.126 -0.024 0.024 Symmetrical
Kurtosis (K) 34.78 3.329 1.079 1.079 Mesokurtic
6 Mean 207.5 2.031 241.4 2.051 Fine sand
Sorting (s) 2.535 0.674 1.585 0.665 Moderately well sorted
Skewness (Sk) -4.400 -0.598 0.144 -0.144 Coarse skewed
Kurtosis (K) 25.93 3.450 0.948 0.948 Mesokurtic
7 Mean 272.0 1.737 302.8 1.724 Medium sand
Sorting (s) 2.178 0.603 1.522 0.606 Moderately well sorted
Skewness (Sk) -5.292 0.276 -0.105 0.105 Fine skewed
Kurtosis (K) 38.32 3.687 1.021 1.021 Mesokurtic
8 Mean 237.5 1.991 252.8 1.984 Medium sand
Sorting (s) 1.845 0.539 1.439 0.525 Moderately well sorted
Skewness (Sk) -5.853 -0.404 0.150 -0.150 Coarse skewed
Kurtosis (K) 53.41 3.911 1.055 1.055 Mesokurtic
9 Mean 248.0 1.855 279.7 1.838 Medium sand
Sorting (s) 2.235 0.626 1.522 0.606 Moderately well sorted
Skewness (Sk) -5.011 -0.040 -0.060 0.060 Symmetrical
Kurtosis (K) 34.82 3.177 0.886 0.886 Platykurtic
10 Mean 198.6 2.285 201.6 2.311 Fine sand
Sorting (s) 1.617 0.480 1.383 0.468 Well sorted
Skewness (Sk) -6.223 -0.388 -0.143 0.143 Fine skewed
Kurtosis (K) 69.79 5.663 1.613 1.613 Very leptokurtic
1 — Besant Nagar, 2 — Thiruvanmiyur, 3 — Panayur, 4 — Kovalam Creek, 5 — Nemmelikupam, 6 — Mahabalipuram, 7 — Kalpakkam, 8 — Perunthuravu, 9 — Periyakuppam, 10 — Aliyakuppam.
Table 1 - Results of grain size analysis of the study area.
activities along the coast have established the intactness and compactness of beach sediments, resulting in the onshore and offshore drifting of sediments. The littoral currents also play a significant role in the redistribution of sediments along the beaches and core stations. The frequency pattern point towards the presence of bimodal distribution having peaked at 2.00 4 and 2.75 4. Mostly fine grained and medium grained are dominated in this region.
2.5. Mean
The mean reflects the overall average size of the sediment as influenced by source of supply and environment of deposition.
In the study area, mean value ranges from 1.8 4 to 3.7 4 indicating a prominent distribution of medium sand in this zone (Fig. 2). In the core station at Mahabalipuram, mean value ranges from 1.69 4 to 2.34 4 indicating a prominent distribution of medium to fine sand in this zone. The distribution of medium sand in this region might have accrued from the dislodging of coarser lighter sediments by the panning action of high velocity waves and also high energy environment.
2.6. Standard deviation
Standard deviation measures the sorting or uniformity of the particle size distribution. Accordingly, in the study region sorting value ranges from 0.46 4 to 0.77 4 (Fig. 3) indicates moderately sorted to moderately well sorted nature may be due to the addition of sediments of different grain size from the reworking of beach ridges or by alluvial action and the prevalence of strong wave convergence throughout the year.
Mahabalipuram core stations sorting value ranges from -0.01 4 to 0.74 4, indicates well sorted to moderately well nature. The moderately sorting nature may be due to the
addition of sediments of different grain size from the reworking of beach ridges or by alluvial action and the prevalence of strong wave convergence throughout the year. Similar observations are found in the East Coast of India (Vijayam, Aswathanarayana, & Mahadevan, 1961). The better sorting (well sorted) at the deeper depth is probably due to the prevalence of wave convergence throughout the year and the finer size of the sediments.
2.7. Skewness
Skewness measures the asymmetry of the distribution. In
general, based on the classification of Folk and Ward (1957) the skewness values of these sands vary from negatively skewed to very positively skewed. In the study region, the sediments show strongly coarse skewed to fine skewed (0.32-0.32) (Fig. 4). It implies the prevalence of high and low energy environments in different wave directions, entailing a mixed distribution of coarse and fine sediments. Due to washing and backwashing of waves, coarser sediments are retained and get entrapped amidst finer sediments.
In the core sample upto 1 m depth shows positive skewed (0.15-0.53) indicate the low energy environment. The low tide and high tide show a similar pattern as negative skewed indicate the high energy environment.
2.8. Kurtosis
The graphic kurtosis is the qualitative measure of the part of sediments already sorted elsewhere in a high energy environment and later transported and modified by another type of environment (Folk & Ward, 1957). But the moment kurtosis is an index of mixing of two-end populations (Thomas, Kemp, & Lewis, 1972). The graphic kurtosis study shows that the area
Stations
Fig. 2 — Distribution of mean values.
Fig. 3 — Distribution of standard deviation.
Fig. 4 - Distribution of skewness.
is mesokurtic to leptokurtic in nature. The very leptokurtic to platykurtic nature indicates multiple environment i.e. one derived from riverine/aeolian environment and the other primarily derived from marine environment (Fig. 5).
The moment kurtosis values are found to vary from 1.7 to 4.1 in the core stations. This uneven nature clearly designates the mixing of two-end populations. The movement of longshore currents and the fluvial discharge of sediments have probably brought out these two populations mixing. This is also attributable to the widely varying nature of sediments and change in gradients of the coastline.
3. Depositional environment
3.1. Bivariant plots
In the present study, various textural parameters obtained through both graphic and movement methods have not shown many variations. Several earlier workers like Moiola and Weiser (1968), Hails and Hoyt (1969), Jaquet and Vernet (1976), Rajamanickam and Gujar (1984, 1993) have also expressed similar views. Mean against skewness plot shows a distinct field of separation between Low water mark, beach and foreshore (Fig. 7). The values of mean and skewness of core stations indicated more fineness and sorting than the beach sands. Standard deviation vs skewness is fall in the low water mark and strandline except a few stations at foreshore environment.
The bivariant plot of mean vs. standard deviation (Fig. 6) shows that the sediments are poorly sorted irrespective of their coarseness or fineness. This emphasizes the fact that sorting is independent of grain size and that sorting deteriorates in both coarse and fine sediments. The plot of mean vs. skewness (Fig. 7) shows that the skewness values vary
from positive to negative with increasing mean sediment size. The scatter plot of mean vs Standard Deviation (Fig. 8) shows a distinct group. It indicates a poorly sorted as mean size decrease. The scatter plot of standard deviation vs. skewness (Fig. 9) also helps to characterize as a separate cluster. The study region shows the influence of fluvial and beach environments (Fig. 10).
4. Heavy minerals
The heavy minerals weight percentages of various locations for beach and core stations are given in Table 2. In the study region, the fine sand receives more number of heavies. Based on Heavy mineral distribution, it is observed that from station 2 & 3, 5 & 6 and 9 records appreciable amount of heavies. From the Table 2, it is clear that the beach shows enrichment of heavy minerals in the finer sediments (Fig. 11 a to J). This corroborates the earlier view (Hanamgond, Gawali, & Chavadi, 1999; Nayak, 1996) along this stretch. This enrichment in the finer grade is mainly due to selective removal of light minerals leaving behind coarser light minerals and high density minerals in H/L ratio (Frihy & Komar, 1991) for the different fractions (0.149-0.062 mm) shows a gradual increasing trend towards finer size and is maximum at the finest size. Our findings also corroborate with Hanamgond and Nayak (2011). At the station 4, 7 & 8, the heavy weight percentage is very less in amount. The beach environment is more amount of Opaque/Non- opaque ratio, garnet colourless and Zircon and lesser amount of garnet pink is noticed. However, the absence of augite and muscovite is noteworthy in beach stations. At Mahabalipuram the depth of 0-10 cm the heavy mineral wt percentage is gradually increases and from the depth of 40 cm to 80 cm an appreciable rise in percentage is noticed.
t: 3 0.8
!£ 0.6
Fig. 5 - Distribution of kurtosis.
2.5 2 1.5 1 0.5 0
♦♦♦ ♦ t ♦ ♦
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Fig. 6 — Mean vs standard deviation.
IA ai 0.1
V •at 0
♦ ♦
♦ ♦
0.5 1 1.5
Fig. 7 — Mean vs skewness.
♦ ♦
4.1. Heavy mineral assemblages for beach and core stations
The heavy mineral assemblage of the study region is governed by the distribution of different type of minerals. However, the assemblage is restricted to the dominance of few selective minerals like garnet colourless, garnet pink, zircon, rutile, tourmaline, chlorite, etc. The study area is characterized by a suite of kyanite (1.21-32.54%), garnet (12.03-31.76%), opaques (6.69-19.12%), and zircon (4.0-20.19%) minerals. Zircon and garnet is found in the high percentages in this region. Chlorite is less dominant in all the zones. The non opaque distribution in the different grain sizes within the sector has established the prevalent presence of chlorite, kyanite, garnet, zircon and tourmaline. From the nature of zircon, it is clear that this sector is influenced by two different source rocks, one in the northern zone dominantly of rounded zircons and the other in the overgrown and out grown zircons.
Provenance
Based on heavy minerals, an attempt has been carried out to find out their parent rocks in the provenance. The minerals like garnet, kyanite, hypersthenes, may be assigned to the contribution of different high grade metamorphic rocks. The opaques (mainly of ilmenite and magnetite), zircon euhedral, topaz and rutile might have been derived from igneous rocks of acidic and basic compositions of the study area. Similarly, the rutile, rounded zircon and the remaining above said minerals having roundness in the range of sub-rounded nature, etching, over growths, out growths, etc., can be related to the ancient sediments which have undergone the recycling. When comparing the different rock types and the mineral assemblages of the study area, it is suggested that along with the high rank metamorphic, acid and basic igneous rocks, reworked sediments and the low rank metamorphic rocks are expected to provide a significant contribution in these
Fig. 8 - Standard deviation vs mean.
Fig. 9 - Standard deviation vs skewness.
environments. From this, it may be concluded that along with the contribution of the minerals from the rock types of study area, some other distant sources might have also been added up to form the mineral assemblage in these environments. The minerals considered from outside contributions may be of mainly from low rank metamorphic rock types.
4.3. Trace elements
Analyses of trace metal distributions in the study area indicate that metal concentrations in sediments are controlled by variations in the reactivity of different particle types and sizes, and natural sources. Geochemical analyses for Fe, Mn, Cr, Cu, Co, Ni, Pb, and Zn were carried out and their mean concentration is listed in Table 3 and Fig. 12a-g.
Fig. 10 - Distribution of heavy and light minerals in the study area.
4.3.1. Iron (Fe)
Iron is the most abundant metal, and is believed to be the tenth most abundant element in the universe. The range in sedimentary iron values between 1.71 and 8.68% with the average of 4.32% in the beach stations. The highest concentration was observed at station no 3 & 6 and the lower concentration was in station no 2 & 8. Overall, concentration of the sedimentary iron was not much variation except some station. The concentration of sedimentary iron in this study not much higher than that reported other coastal areas of India and worldwide. The Iron in the study area was relatively low than the average continental crust values (Wedepohl, 1995).
4.3.2. Manganese (Mn)
Manganese is a very common compound that can be found everywhere on earth. Manganese in the surface sediments of study area ranges from 158 to 2203 mg g-1. The highest concentration was recorded at station no. 3 & 6 which are in middle transect. The lowest concentration was observed at station no. 2 & 8. The Mn concentration was relatively lower than the average continental crustal values. Manganese is relatively abundant with an average upper crustal abundance of 600 mg kg-1 and a bulk continental crust average of 1400 mg kg-1 (McLennan & Taylor, 1996). It's indicating the manganese in sediments is only from the lithogenous origin, there is no anthropogenic input in the study area. The concentration was low at southern part and relatively high in middle region. This is due to the grain size effect in the marginal marine sediments, where the fine grain sediments accumulate there will be high concentration of metals. This is well supported by the grain size, fine sediments were high at Mahabalipuram of the study area.
4.3.3. Chromium (Cr)
The study area results show that the chromium variation is from 37 to 1720 mg g-1 with an average of 382 mg g-1; the contamination factor of Chromium is >4 also indicates the chromium contamination is relatively higher in sediments, when compared with the world average crustal values (Wedepohl, 1995). The highest value was observed in station no. 3, 5, 6, & 7 and the lowest at remaining stations. The enrichment of chromium is mainly due to the dumping of effluents from the nearby industries of the study area. Chromium also show high positive correlation with lead and
Table 2 - Heavy mineral weight % of the study area.
Stations Coarse Medium Fine
Phi values 0.149 0.125 0.105 0.088 0.074 0.062
Besant Nagar 0.247 0.238 0.257 1.12 2.201 4.125
Thiruvanmiyur 0.014 0.417 0.124 2.142 3.125 5.451
Panayur 0.101 0.121 0.022 1.012 1.587 2.114
Kovalam Creek 0.113 0.114 0.123 0.127 1.158 2.247
Nemmelikuppam 0.121 0.104 0.102 1.111 2.102 4.124
Mahabalipuram 0.158 0.874 0.124 1.011 2.123 2.147
Kalpakkam 0.014 0.365 0.254 0.127 1.248 2.548
Perunthuravu 0.12 0.921 0.554 0.625 1.114 1.104
Periyakuppam 0.014 0.016 0.117 1.742 1.147 3.311
Aliyakuppam 0.321 0.121 0.141 1.471 2.147 3.128
Zinc indicating the anthropogenic influence in the marginal marine sediment which is due to the occupational exposure of numerous processes including chrome plating baths, chrome colours and dyes, cement, tanning agents, wood preservatives, anticorrosive agents, welding fumes, lubricating oils and greases, cleaning materials, textiles and furs.
4.3.4. Copper (Cu)
Copper content varies in study area stations from 22 to 432 mg g-1 with an average of 96 mg g-1. The highest concentration was observed in station no. 1 and the lowest was observed in all the remaining stations. The higher concentration of Cu in station S1 it may due to the organic matter and Fe-Mn oxyhydroxides produce simultaneous accumulation
Coarse
medium
Coarse
medium
Coarse
medium
Coarse
1.5 1 0.5 0
Coarse
Coarse
medium
--• 1 *
Coarse
medium
Coarse
medium
medium
medium
Fig. 11 - (a) Heavy wt % in Besant Nagar; (b) heavy wt % Thiruvanmiyur; (c) heavy wt % Panayur; (d) heavy wt % Kovalam Creek; (e) heavy wt % Nemmelikuppam; (f) heavy wt % Mahabalipuram; (g) heavy wt % Kalpakkam; (h) heavy wt % Perunthuravu; (i) heavy wt % Periyakuppam; (j) heavy wt % Aliyakuppam.
Table 3 - Results of trace element geochemistry in the study area (mg g >
S. no. Fe Mn Cr Cu Pb Zn Co Ni
Average continental crustal values 78 92 28 17 67 17.3 47
1 5874 720.8 540 211 59.8 89 48 63.2
2 5418 318 677.2 105.6 53 80.6 16.4 90.8
3 6020 982.4 1665 99.4 55.4 112 37.4 165.8
4 5646 494.2 257.2 118 36.4 110.6 18.2 59.2
5 5978 863.8 1285.6 10.8 55.8 86.4 38.8 154.2
6 6382 2756 1232.6 35.6 173.6 210.4 79.2 186.8
7 5688 472 1233.8 33 37.6 75.4 33 146.8
8 5442 331.2 227.6 39 23.6 80.2 30 44.6
9 5816 705.2 279 11.2 26.2 101.6 26.4 48.6
10 5772 638.8 723.6 27.4 36.4 111.2 26.2 12.6
heavy metals in sediments (Lisbeth, Lepkova, Katarina, & Martin, 2006). In particulate contamination derived from boating activities, and in particular, paint chips or flakes resulting from the annual cleaning (e.g. pressure-hosing) or, less frequently, complete scraping (shot blasting, sanding, stripping) of automobiles (Turrner, Fitzer, & Glegg, 2008). The Cu concentration is higher in all along the dumping yards indicates the Cu is mainly due to the anthropogenic origin.
4.3.5. Lead (Pb)
The analytical results shown that the lead varies from 10 to 209 mg g-1 with an average of 37 mg g-1. The highest concentration of Pb in station no. S6 and the lowest were observed in all the remaining stations. Lead values in bay, estuarine and other coastal sediments have been much altered by man's activities (Alagarsamy, 2006). This Pb concentration was lower than the coastal sediments and some other marginal marine areas. The concentration of Pb was low due to the dilution of monsoonal rainfall. The higher concentration of Pb indicates the contamination in sediments, when compared with the world average crustal values (Wedepohl, 1995).
4.3.6. Zinc (Zn)
Zinc occurs naturally in air, water and soil, but zinc concentrations are rising unnaturally, due to addition of zinc through human activities. The concentration of Zinc varies from 33 to 2197 mg g-1 with an average of 240 mg g-1 in surface sediments. The highest concentration was observed in station no. 6 and the lowest observed in the remaining stations. The zinc concentration was relatively higher than the world average soils. The highest concentration of zinc is mainly due to input of organic wastes in aquatic environment, which comes from municipal sewage, and dumping materials contributes to the zinc increase in sediments (Alagarsamy, 2006). Zinc can enter the aquatic environment from a number of sources including industrial discharges, sewage effluent and runoff (Boxall, Comber, Conrad, Howcroft, & Zaman, 2000).
4.3.7. Nickel (Ni)
Nickel is a compound that occurs in the environment only at very low levels and is essential in small doses but it can be dangerous when the maximum tolerable amounts are exceeded. The nickel concentration in the study area varies from 13.9 to 487 mg g-1 with an average of 85 mg g-1. The nickel concentration was relatively high with compared to other
coastal and average sediments. This is due to the monsoonal effect and fresh water input has diluted the concentration of Ni in the beach sediments. In Nickel concentration is trend to increase towards the northern side of the stations.
4.3.8. Cobalt (Co)
Cobalt is relatively scarce in the earth's crust. Cobalt occurs in di- and tri-valent state in rocks. Its migration in sea water and its geochemistry is almost slightly higher than that of Ni. The Co concentrations are product of three main sources: i) Co fixed in the lattice position of clay minerals, ii) Co precipitated from overlying water column and iii) Co association with organic matter. The average concentration of Co in ultramafic rocks is 110 ppm, in mafic rocks it is 48 ppm, in granitic rocks it is 1 ppm, in soils it is 10 ppm, in plant ash 5 ppm, and in fresh water is 0.1 ppb. Its chalcophile associations are Mg and Ni in mafic and particularly in ultramafic rocks. It is present in mafic minerals. Its weathering products are carbonates and hydroxides, adsorbed and co precipitated Mn oxides or, to a less extent, Fe oxides. Its aqueous species are Co2+ and organic complexes. Cobalt is one of the more important trace elements in animal nutrition. Mobility of Co is intermediate, controlled mainly by adsorption and co-precipitation with Fe-and Mn-oxides. The highest values are noticed in station no 3, 5, 6, 7 and lowest value in station no 10. This indicates that the concentration of Co present in the sediments of the study area is associated with lithogenic origin with little contribution from external sources.
5. Discussion
Based on the heavy mineral studies, it is clearly observed that the coastal region between Besant Nagar and Marakkanam is lesser percentages of heavy mineral distribution than the other coastal regions. Opaque minerals are slightly higher than the non opaque minerals in this region. Only selective minerals like garnet, zircon and tourmaline are dominated. The lesser percentage of chlorite, hypersthene, hornblende, etc., are noticed. The coastal morphology may control the distribution of placer deposits. This is also supported by Anbarasu (1994) who clearly explained that coastal morphology is the controlling factor for the distribution of placer deposits. A large quantity of sediments is supplied by the major rivers along the east coast and is constantly moved
6500 6000 Î5 5500
5000 4500
123456789 10
Stations
3000 2000
3 1000 0
123456789 10
Stations
rH 1500 à 1000 500 0
123456789 10
Stations
^N—» ♦
Fig. 12 — (a) Distribution of Fe concentration; (b) distribution of Mn concentration; (c) distribution of Cr concentration; (d) distribution of Cu concentration; (e) distribution of Pb concentration; (f) distribution of Zn concentration; (g) distribution of Co concentration; (h) distribution of Ni concentration.
by the waves either towards the north or south depending on the angle of wave approach with respect to the coast. The rate of sediment transport varies from time to time along the coastal region. Analysis presented (Chandramohan, Nayak, & Raju, 1990) indicates that the transport is towards the north from March to October and towards the south from November to February. Northerly and southerly components of the annual sediment transport along the Chennai to Mahabalipuram are estimated to be in the order of 0.89 and 0.60 x 106 m3, respectively. This results in a net northerly drift of 6 m3 per year. Due to the littoral drift and sediment transport the heavy percentage are also varied in this region.
Over all from the geochemistry studies it is observed that the Ni and Cr are more dominant and higher concentration in Panayar (station no. 2), Mahabalipuram (station no. 6), Kalpakkam (station no. 7) and Perunthuravu (station no. 8). The percentage distribution of the Total heavy mineral concentration by weight with respect to station to station of individual grain sizes exhibit in beach and core station environments display hardly any significant trend. This may be due to the fact that these environments are influenced by different factors in different times at a particular point. According to Hanamgond and Nayak (2011) the concentration of heavy metals/elements is controlled by the particle size. It is reported that, adsorption of heavy metals is inversely related to the particle size, where finer particles due to their high specific area, adsorb more heavy metals. The available minerals and their chemical weathering/leaching effect mainly influence the distribution of elements in both the grain size fractions. Textural study of present day sediments as well as studies of Mohan and Rajamanickam (1995), indicate that mixed energy environment and erosion activities are more in this region. Because of this nature, the contribution of heavies are not showing any typical trend which in turn, reflect the process of sedimentation which could not concentrate the heavies by removal of more light minerals from this region.
At Mahabalipuram shore temple, towards south of the bay, heavy mineral concentration is relatively less on the surface. In order to get the enrichment of heavy minerals as beach placers, the optimum conditions are required which should be neither erosive nor accumulative in nature. Such conditions prevail in stable shores, which are signified by the presence of open seashore face, sandy beach, cliffs and high coasts. In the berm region, alternate heavier and lighter mineral bands with increasing width of heavy mineral bands with depth are noticed. About 70 m south of the shore temple, rock exposures constituted by graphic granite, pyrope garnet with reddish-brown colour and labradorite were observed. The littoral drift bringing the oceanic sediments especially in the northeast and southwest monsoon enter inside this region. As they are getting refracted at the coastline, they return with the added force (a circular current or swirl) and leave out the Mahabalipuram with the coarser light fraction and fine heavies. The continuous processes of such movement enable the sediments in and around Mahabalipuram to get enriched in heavies. The persistence of sand throughout the region in all depths is enriched in heavies. The persistence of sand throughout the region in all depths is supplementing such possibilities.
6. Conclusion
In the study area most of the sands are fine and medium grained indicates beach environment and most of the grains are positive skewed with very platykurtic to leptokurtic indicates multiple environments. Most of the grains are very well sorted to moderately well sorted may be due to addition of sediments of different grain size from the reworking of beach edges or by fluvial action. The heavy mineral assemblage of the study region is governed by the distribution of different type of minerals. However, the assemblage is restricted to the dominance of few selective minerals like garnet colourless, garnet pink, zircon, rutile, chlorite, etc. The study area contained a high percentage of orthopyroxene (hypersthene) and garnet, rounded and broken zircons inferred to have been derived from charnockites and granulite gneiss.
From the geochemistry studies, very low concentrations of Fe are found in Marakkanam but sediment core from Mahaba-lipuram shows relatively higher values Mn concentrations are generally high in the sediments of Mahabalipuram due to the variability of the source rocks exposed in this region, On the other hand, Zn at Marakkanam show relatively low Zn values our results clearly indicate that Ni and Cr are high in sediments of Besant Nagar to Marakkanam could be due to the effect of rapid mixing of open waters with the estuarine waters of nearby regions. High values of Cr and Ni are also attributed to intense.
The present study has clearly indicated the multiple roles of tectonically controlled coastal blocks and their geomor-phological influence in redistributing the sediments with favourable NE-SW configuration and wave energy conditions must have contributed to the formation of heavy minerals in a particular zone. As these factors play a major role the materials derived from a common provenance are regrouped for density and size sorting process. Further, the heavy mineral assemblage of the core sediments with respect to the nature of catchment rocks of the study region indicate the possibility of mineral supply from additional agencies such as alongshore and offshore sources.
Acknowledgement
The authors are sincerely thankful to Prof. S.P. Mohan, Professor and Head, Department of Geology, University of Madras, Chennai - 25 for provide lab facilities to carry out this work. The authors are highly acknowledges the anonymous referees for improving this manuscript at various stages for publication.
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