A study on textural characteristics, heavy mineral distribution and grain-microtextures of recent sediment in the coastal area between the Sarada and Gosthani rivers, east coast of India

International Journal of Sediment Research 35 (2020) 484e503

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International Journal of Sediment Research journal homepage: www.elsevier.com/locate/ijsrc

Original Research

A study on textural characteristics, heavy mineral distribution and grain-microtextures of recent sediment in the coastal area between the Sarada and Gosthani rivers, east coast of India Ali Mohammad*, Parvathaneni Bhanu Murthy, Edupuganti Naga Dhanamjaya Rao, Hari Prasad Department of Geology, Andhra University, Visakhapatnam 530003, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 25 April 2019 Received in revised form 9 March 2020 Accepted 12 March 2020 Available online 19 March 2020

The current study aimed to describe textural characteristics, heavy mineral composition, and grain microtextures of the sediment from three micro-environments (foreshore, berm, and dune). A total of forty-one (41) representative surficial sediment samples have been collected from fifteen (15) locations along the beach area between the Sarada and Gosthani rivers on the east coast of India, where the length of the stretch is more than 100 km. The study reveals that most of the coastal sediment is medium to fine sand with relatively high ratios of coarse sand at Yarada beach, and the nature of the sediment is moderately to well sorted. These characteristics indicate a high energy environment. The heavy mineral analysis of the sediment in the current study was done for coarse (þ60#) and fine (þ230#) size fractions. Studying the weight percentage (WT%) reveals that a high percentage of heavy minerals is associated with fine fractions. Ilmenite, sillimanite, garnet, zircon, and rutile are the major heavy minerals identified in the current investigation. The concentrations of these heavy minerals show great variations from south to north of the study area. From an economic point of view, a considerable amount of heavy minerals (average 48.41%) are present on both sides (north and south) of the Gosthani River mouth. In the Sarada Estuary, the concentration of the economic heavy minerals was found under the minimum economic range. The grain microtextures of the major heavy minerals from the different locations along the study area demonstrate the variation in grain microtextures, which is controlled by the chemical and mechanical processes. These microtextures reflect moderate to high wave energy on the beach area, in addition to high mechanical impact on the grains from the estuary point. © 2020 International Research and Training Centre on Erosion and Sedimentation/the World Association for Sedimentation and Erosion Research. Published by Elsevier B.V. All rights reserved.

Keywords: Textural characteristics Heavy minerals Grain microtexture Coastal sediment Visakhapatnam Coast

1. Introduction Coastal sediment is the result of the processes acting on the preexisting rocks. The study of the recent sediment uncovers essential information about the geographical and geological history of the recent past of the particular area under study. There has been a growing interest in studying modern sediment in recent years. These studies have opened up new fields of crucial economic resources exploration (Anonymous, 2000; Freeman et al., 2003; G. Banergee & D. Banergee, 2005; Harben, 2002; Mange & Wright, 2007; Raju et al., 2001; Summerhayes, 1967; among others). This

* Corresponding author. E-mail address: [email protected] (A. Mohammad).

unconsolidated sediment contains different types of minerals which are classified as valuable minerals (such as, barium, chromium, gold, iron, rare earth elements, tin, thorium, tungsten, and zirconium), and rock-form minerals (such as, feldspar, garnet, silica, etc.) (Sharma & Ram, 1964). Finding and extracting these valuable minerals poses a big challenge for countries and companies because the concentration of the typical heavy mineral sand ore deposit is usually found in low amounts (Berquist et al., 1990; Brown et al., 2009; Gent et al., 2005; Lenoble et al., 1995; Li & Komar, 1992; Noakes, 1977; Perissoratis et al., 1987; Praditwan, 1988; Roy, 1999). Modern sediment forms a stretch of varying width adjacent to marine water bodies all over the world. The composition of this modern sediment depends on the rock sources surrounding them. In general, sediment particles are transported from continental rocks by means of mechanical erosion and then

https://doi.org/10.1016/j.ijsrc.2020.03.007 1001-6279/© 2020 International Research and Training Centre on Erosion and Sedimentation/the World Association for Sedimentation and Erosion Research. Published by Elsevier B.V. All rights reserved.

A. Mohammad et al. / International Journal of Sediment Research 35 (2020) 484e503

accumulate and concentrate under appropriate conditions to be form placer deposits. The placer deposits are probably considered as economically viable deposits depending on the weight percentage of total heavy minerals (THM) from the representing samples of that particular deposit. Thus, out of all sediment transporting media, rivers are considered as the main transporting agent from source to deposition areas, where the sand particles are sorted by water motion (waves, tides, and currents) according to the varying density (mass per unit of volume) of the constituent minerals (Komar & Wang, 1984). During the sediment journey, variable chemical and physical changes occur to these particles (Boggs, 2006). The Indian peninsula is surrounded by three seas, namely, the Arabian Sea (west), Indian Ocean (south), and Bay of Bengal (east), covering a coastal length of about 6,500 km and showing its significance at different levels. In a commercial way, Indian coasts are fortunate to have considerable amounts of heavy mineral wealth, more than other countries. Comparatively, India has played a pioneering role among the heavy mineral producing countries. Andhra Pradesh (AP) has a costal bar along the eastern part of India with a coastal length of 974 km. This area receives huge amounts of terrigenous materials which result from erosion and decomposition of igneous and different metamorphic rocks from the Eastern Ghat Mobile Belt (EGMB). The parent rocks formed from mixed origin (both igneous and metamorphic) resulting in variety in the composition. Heavy minerals are the main characteristic feature of the beach area of AP (Cheepurupalli et al., 2012; Deva Varma et al., 1989; Mahadevan & Nateswara Rao, 1950; Mahadevan & Sriamdas, 1948; Mohan & Rajamanickam, 2000; Mohapatra et al., 2015; Panda et al., 2002; Ramamohana Rao et al., 1982; Reddy et al., 2012; Sastry et al., 1981, 1987; Sriramadas, 1951; Subrahmanyam et al., 1982), and these heavy minerals also can exist in high concentrations, especially in areas adjacent to the large river estuaries (Rao et al., 1993). Prof. La Fond and Prasada Rao (1954, 1956) from Andhra University studied the various aspects of recent sediment and the depositional environments. This could be considered as the first attempt to study the recent sediment of the Visakhapatnam coast. Later, many studies were done in the area between Visakhapatnam and Bhimunipatnam, and such studies have examined various aspects in different facets. However, less work has been done on the southern area of the current study area (southern part of the Visakhapatnam Coast). Thus, in the current investigation, the southern and northern sides of Visakhapatnam Coast are examined in order to give a clear understanding of the depositional processes and environments. The current study is exploratory in nature, with the main aim of drawing a general frame work of the distribution of sediment and heavy minerals concentration, in addition to examining the economic quantity of the useful heavy minerals within both sides of the study area, and highlighting the best location for heavy minerals mining. Moreover, the current study provides a stone corner for future investigations of beach sediment as potentially renewable resources of heavy minerals.

2. The study area The current study area is a part of the Visakhapatnam Coast of the Bay of Bengal (see Fig. 1). The study area is located between 17 23ʹ and 17 55ʹ N and 82 23ʹ and 83 29ʹ E with a beach stretch of approximately 100 km. Visakhapatnam is the headquarters of Visakhapatnam district, and it is located in the central part of the study area, due to that, the current investigation has been divided

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into two parts, namely, southern and northern relative to Visakhapatnam's location. Visakhapatnam has a tropical wet and dry climate. The annual mean temperature ranges between 24.7 and 30.6  C (76e87  F), with the maximum in the month of May and the minimum in the month of January; the minimum temperatures ranges between 20 and 27  C (68e81  F). Likewise, the current study area between the Sarada and Gosthani rivers falls under a tropical climate, i.e., humid mega thermal with seasonal rainfall controlled by the monsoon. The rainfall occurs mainly in the south-west monsoon period (JulyeSeptember) and in the north-east monsoon (October). The average rainfall in the area varies from 900 to 1500 mm per year. The study area is located in the eastern part of the Eastern Ghat Mobile Belt (EGMB). This area is bounded by the Bay of Bengal on the east and EGMB on the west. EGMB consists of detached hills that range from 30 to 594 m above MSL (Mean Sea Level). The Kailasa and Yarada ranges are the most obvious hills in the area. Precambrian khondalite and charnokite constitute the main rock formation of these hills (King, 1886; Murthy, 1961; Narasimha Rao, 1945). The beach area from Visakhapatnam and Bhimunipatnam is slowly changing due to coastal processes (waves and tidal currents) (Kannan et al., 2016; Nooka Raju & Vaidyanadhan, 1971). Therefore, these changes make drawing an accurate coastal line a troublesome mission. The Visakhapatnam coast exhibits many geomorphological features. Jagannadha Rao et al. (2012) studied the costal geomorphology between Visakhapatnam and Bhimunipatnam, where he classified coastal features in three types according to the formation processes, such as: waves, sea level oscillation, and the interaction between rock and sea water. Sandy beaches, dunes, and rocky beaches are the main features that characterize the study area. In addition to that, red sediment (bad lands) located near Bhimunipatnam (Gosthani River estuary) can be determined as the unique topography neighboring the study area. 3. Materials and methods Forty-one representative surficial sediment samples were collected at fifteen locations (see Fig. 1) from three microenvironments (foreshore, berm, and dune) along the study area. While collecting the samples, the sampling covered rivers, streams, channels, and estuaries present in the study area, i.e., one sample from each environment. However, at some locations, the dune environment was missing. 3.1. Grain size analysis All forty-one surficial sediment samples had a hundred grams sub-sample taken from each sample by coning and quartering the original sample. Then, the representative sub-samples were washed using distilled water to purify them from salts. The salt free samples were processed by diluted hydrochloric acid (HCl) (1:10) to remove shell fragments and carbonate materials, where this process takes about 12 h. Later on, the washed samples were treated with (1:10) hydrogen peroxide (H2O2) to remove organic matter. Usually this process takes an overnight to achieve good results. Oven dried samples were subjected to the standard ASTM sieves at ½ Ø interval for fifteen minutes on a Ro Tap sieve shaker. The sieves were subjected to the G-Stat computer program (Appa Rao & Karuna Karudu, 2018; Chauhan et al., 2014) to determine the grain size parameters [Mean size (Mz), standard deviation (s1),

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Fig. 1. Location map of the study area (note: NH5 is the national highway 16 in India).

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skewness (Sk) and kurtosis (KG)] following the Folk and Ward (1957) method. 3.2. Heavy minerals analysis Among the selected sieved materials, the following two size fractions, namely, sieves þ60# (0.25 mm, coarse sand) and þ230# (0.25e0.063 mm, fine sand) have been used for heavy mineral separation. In order to remove the oxide coating, these fractions were washed with stannous chloride (SnCl2). The foregoing washed size fractions were rushed for drying and then subjected to heavy mineral separated by using heavy liquid (Bromoform, CHBr3, specific gravity ¼ 2.89) through the float and sink method (Milner, 1962). Acetone was used to deodorize and remove the traces of the used Bromoform from the heavy mineral grains' surface. Taking into account the fugitive character of acetone, hot air oven (60  C) was used to dry the separated heavy mineral grains. Then, the heavy and light fractions were weighed and their weight percentages were calculated. The heavy minerals were mounted on a glass slide with Canada balsam. Thin slides (with 200e300 grains) were studied using a Petrological microscope with a mechanical stage.

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Ribbon counting methods were used for heavy minerals counting (Galehouse, 1969). Weight percentage (WT%) was calculated by multiplying the number of individual minerals in the slide by the specific gravities of each mineral. Whereas, the total heavy minerals (THM) for the bulk sample was calculated by summing the WT% for both fractions. 3.3. Grain microtexture of heavy minerals For grain-microtextures of heavy minerals, Scanning Electron Microscopy (SEM) is the perfect instrument to do this task. Four locations were chosen for the microtexture study, from these locations, many heavy mineral grains (10e30 for each) were picked up using a microscope. All grains have been identified before fixing them on the SEM stage. Gold coating was done for every grain to improve the imaging of the sample. 4. Results and discussion A detailed study has been done for the coastal samples to determine the grain size parameters, such as, mean, standard

Table 1 Grain size parameters of the coastal sand from the area between Sarada to Gosthani rivers on the east coast of India (note: SD ¼ standard deviation, No. ¼ number, V ¼ very). Skewness Kurtosis Sand Silt

Clay V coarse sand Coarse sand

Medium sand

Fine sand V fine sand Sorting typea

Skewness typea

Kurtosis typea

0.638 0.383 0.736 1.106 0.853 0.694 0.721 0.549 0.729 0.758 0.803 0.576 0.481 0.554 0.562

0.045 0.23 0.009 0.06 0.263 0.017 0.207 0.016 0.181 0.242 0.271 0.268 0.104 0.152 0.212

1.581 0.925 0.97 0.924 1.308 1.201 1.103 0.874 1.244 1.142 0.762 0.898 1.35 0.925 1.183

99.19 99.62 99.27 98.67 98.60 97.21 99.91 99.35 99.48 99.83 99.95 99.30 99.81 99.37 99.81

0.801 0.376 0.729 1.327 1.395 2.786 0.087 0.647 0.517 0.162 0.043 0.699 0.186 0.625 0.181

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1.227 0 0.227 3.033 0.834 0.577 3.864 0.038 0.59 5.125 12.483 0.02 0.248 0.055 0.433

5.619 0.069 8.687 19.752 9.069 1.124 22.967 0.973 10.733 21.46 20.504 1.793 5.045 0.668 3.661

65.215 43.449 49.898 33.27 24.909 16.924 62.027 39.463 62.25 61.79 56.711 62.903 74.074 40.806 64.729

24.366 54.405 36.455 34.212 56.453 58.852 10.514 54.083 23.002 10.693 9.902 30.752 18.661 50.855 27.054

2.772 1.7 4.004 8.405 7.339 19.737 0.54 4.796 2.908 0.77 0.356 3.832 1.786 6.992 3.942

Mws Ws Ms Ps Ms Mws Ms Mws Ms Ms Ms Mws Ws Mws Mws

Sy Fsk Sy Sy Csk Sy Csk Sy Fsk Csk Csk Fsk Fsk Fsk Fsk

Vlk Mk Mk Mk Lk Lk Mk Pk Lk Lk Pk Pk Lk Mk Lk

0.459 0.42 0.46 0.588 0.641 0.456 0.73 0.588 0.732 0.555 0.411 0.449 0.682 0.459 0.471

0.227 0.39 0.239 0.001 0.013 0.207 0.02 0.251 0.031 0.13 0.093 0.344 0.132 0.069 0.117

0.964 0.966 0.976 1.296 1.502 1.555 0.881 1.206 1.109 0.889 1.389 0.957 0.937 1.436 1.208

99.20 99.20 99.5 98.41 96.68 97.51 99.91 97.84 99.52 99.54 99.88 99.40 99.53 98.85 99.45

0.791 0.792 0.5 1.586 3.314 2.487 0.089 2.158 0.479 0.452 0.117 0.598 0.461 1.147 0.547

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 2.01 0.009 1.682 0.029 0.518 0 0.2 0 0

0.439 0 0.534 0.187 0.315 0.044 31.936 0.372 5.412 0.589 2.677 0.095 1.809 0.031 0.123

44.554 49.267 48.045 12.363 13.039 2.685 54.803 38.328 51.609 39.862 75.493 53.279 43.61 5.173 11.485

50.201 46.405 47.377 64.703 65.254 72.121 10.442 53.86 35.858 50.765 20.544 42.467 44.178 67.488 71.535

4.014 3.536 3.544 21.162 18.078 22.663 0.721 5.273 4.96 8.303 0.651 3.561 9.743 26.161 16.311

Ws Ws Ws Mws Mws Ws Ms Mws Ms Mws Ws Ws Mws Ws Ws

Fsk Vfs Fsk Sy Sy Fsk Sy Fsk Sy Fsk Sy Vfsk Fsk Sy Csk

Mk Mk Mk Lk Vlk Vlk Pk Lk Mk Pk Lk Mk Mk Lk Lk

0.414 0.621 0.512 0.452 0.491 0.582 0.49 0.388 0.592 0.521 0.456

0.14 0.219 0.108 0.047 0.194 0.196 0.293 0.557 0.046 0.159 0.306

0.88 1.182 1.277 1.429 1.671 0.958 0.949 0.966 1.035 0.818 1.07

99.31 98.65 97.92 98.1 97.26 98.94 99.31 99.46 99.18 99.59 99.79

0.685 1.347 2.077 1.9 2.735 1.055 0.69 0.538 0.818 0.405 0.208

0 0 0 0 0 0 0 0 0 0 0

0 0.134 0 0 0 0 0 0 0.034 0 0

0.128 1.336 0.063 0.011 0.006 0.426 0.071 0.043 0.478 0.06 0.275

34.186 42.432 9.482 7.112 4.247 42.122 41.963 54.061 30.031 26.098 59.731

61.362 49.068 72.446 77.67 74.336 49.29 51.894 41.582 58.006 60.502 36.113

3.639 5.683 15.931 13.307 18.676 7.107 5.381 3.777 10.632 12.936 3.674

Ws Mws Mws Ws Ws Mws Ws Ws Mws Mws Ws

Fsk Fsk Fsk Sy Fsk Fsk Fsk Vfsk Sy Csk Vfsk

Pk Lk Lk Lk Vlk Mk Mk Mk Mk Pk M

Location Mean SD Foreshore L1/A 1.814 L2/A 2.13 L3/A 1.89 L4/A 1.69 L5/A 2.18 L6/A 2.63 L7/A 1.22 L8/A 2.18 L9/A 1.73 L10/A 1.20 L11/A 1.11 L12/A 1.92 L13/A 1.70 L14/A 2.21 L15/A 1.88 Berm L1/B 2.13 L2/B 2.12 L3/B 2.09 L4/B 2.67 L5/B 2.67 L6/B 2.84 L7/B 1.15 L8/B 2.22 L9/B 1.96 L10/B 2.23 L11/B 1.75 L12/B 2.08 L13/B 2.18 L14/B 2.82 L15/B 2.60 Dune L1/C 2.23 L3/C 2.15 L4/C 2.62 L5/C 2.62 L6/C 2.79 L7/C 2.22 L10/C 2.21 L11/C 2.13 L12/C 2.35 L13/C 2.46 L15/C 2.01

a Note: Mws: Moderately well sorted, Ms: Moderately sorted, Ws: well sorted, Ps: poorly sorted, Sy: symmetrical, Fsk: fine skewed, Vfsk: Very fine skewed, Csk: Coarse skewed, Mk: Mesokurtic, Pk: Platykurtic, Lk: Leptokurtic, Vlk: Very leptokurtic.

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deviation, skewness, and kurtosis and also the heavy minerals distribution within the study area (Table 1). 4.1. Grain size parameters The samples from the beach area show a sandy nature, with various ratios of grain size within the three sub-environments (foreshore, berm, and dune). 4.1.1. Mean grain size (Mz) The mean grain size represents the granular structure of the overall grains of the sample, which can give a perception of the dominant grain size. From one facet, the nature of sediment (or) the dominant grain size reflects the nature of the coast, and in another facet, the grain size is used to distinguish between high and low energy environments (waves, currents, etc.) (Amaral, 1977; Nordstrom, 1977). Sediment from the foreshore (see Fig. 2) show medium (1e2Ø) to fine (2e3Ø) grain sizes, where the medium grain size is dominant in most samples (average 50.56%). The medium grain size is a result of the accumulation of medium-sized grains at the expense of washing the light coarse grains (Suresh Gandhi & Raja, 2014). The ratio of the coarse grains is very low in most of the samples (average 8.8%). Whereas at some locations it shows a drastic change, those are Location 7, Location 10, and Location 11 at 22.97, 21.46, and 21.50%, respectively. Nordstrom (1977) found that the differences in grain size statistics are related to the variances in the wave energy and direction on each beach. Samples from the Sarada and Gosthani river estuaries show fine sand with ratios 54.405 and 50.855%, respectively. The fine tendency of the estuary sediment reflects the combined effect of the beach processes and the river flow (Nittrouer et al., 1983). The fine ratio at other locations shows a wide range from 9.9% (Location 11) up to 58.85% (Location 6). Silt and clay ratios at all locations show very low values which range from 0.043% (Location 11) to 2.78% (Location 6). Variation in the grain size of the sediment along the study area is a result of dissimilarity in nature, intensity of the process (Saravanan et al., 2013) and

morphodynamics along the beach (Dora et al., 2014). Sediment from the berm environment (see Fig. 2) is characterized by fine to medium sand, and the ratio of fine grains shows high values at all locations (average 49.54%) except for Yarada Beach (Location 7), which shows medium sand (54.8%) to coarse sand (31.9%) with a mean size value of 1.52 Ø. While in the dune environment, most of the samples show fine sand with mean size values ranging from 2.018Ø up to 2.797Ø. Dunes at Yarada Beach (Location 7) show almost equal proportions of medium and fine sand (42.12 and 49.3%, respectively) and low proportion of coarse grains (0.5%). Mason and Folk (1958) found that the main factor affecting the distribution of dune grain size depends on the distribution of berm and backshore grain sizes. 4.1.2. Standard deviation of grain size (s1) According to Folk (1974), the inclusive Graphic Standard Deviation (s1) is the best overall measure of sorting. For this the following formula was presented s1 ¼ (Ø84  Ø16)/4 þ (Ø95  Ø5)/ 6.6, which comprises 90% of the grain-size distribution. Ø84, Ø16, Ø95, and Ø5 represent the vertical projection of the cumulative curve on the Ø axis. The results of this formula are expressed as “Ø”, where Ø (or Krumbein phi) is the diameter of the particle in “phi”, and it is given by the formula Ø ¼ log 2(D/D0); where D is the diameter of the particle in “mm”, and D0 is the reference diameter which equal to 1 mm. Grain size sorting is a mirror of the deposition basin energy (Roy & Biswas, 1975). The values obtained from the foreshore environment (see Fig. 3) show moderately well sorted (0.5e0.7Ø) to moderately sorted sediment (0.7e1Ø) with values ranging from 0.38 to 1.106Ø (average 0.68Ø) in most of the locations except for Location 4, which shows poor sorting (with a value of 1.106Ø). This extreme value is the result of the mixture of two sand modes, i.e., coarse and fine modes, where the percentage of the coarse mode is 22.78% and 42.61% for fine mode. It has been observed that the dominance of well sorted to moderately well sorted nature is a reflection of the high waves and strong shore currents along the coast (Biju Sabastian et al., 2002). The Sarada River Estuary sediment is well sorted

Fig. 2. Mean size from foreshore, berm, and dune environments along the study area.

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Fig. 3. Standard deviation from foreshore, berm, and dune environments along the study area (Note: Vws: Very well sorted, Ws: Well sorted, Mw: Moderately well sorted, Ms: Moderately sorted, and Ps: Poorly sorted).

with the s1 value of 0.383Ø. There are small changes in the Gosthani River estuary, where the sorting shows moderately well sorted with a s1 value of 0.554Ø. In general, well sorted sediment in a river estuary area indicates the equal intermingling processes of the sediment from the sea and the river (Singarasubramanian et al., 2006). The values derived from the berm environment (see Fig. 3) indicate the predominance of well sorted sediment in most of the locations under investigation, with values ranging from 0.41Ø to 0.73Ø and an average of 0.54Ø. The same is shown in the dune sediment, which have values ranging from 0.39Ø to 0.62Ø (average 0.5Ø), and the standard deviation values belong to the categories from moderately well sorted to well sorted. 4.1.3. Skewness (SK1) Skewness is a measure of the proportion of coarse or fine fractions within the sediment, and it is very helpful to understand the near shore processes. Folk and other scientists who have worked on sediment (Chappell, 1967; Duane, 1964; Folk & Ward, 1957; Friedman, 1961, 1967) suggested that the skewness is the best indicator and the most sensitive parameter to environmental changes. Skewness values from the foreshore sediment (see Fig. 4) oscillating between 0.27 and 0.27Ø and trending from coarse to fine skewness. The Sarada and Gosthani river estuaries sediment show a dominance of fine skewness. The fine skewed nature indicates that the sediment which were carried by the rivers has an excess of fine particles (Angusamy & Rajamanickam, 2006). The skewness value derived from Yarada Beach (Location 7) shows coarse skewness. On the other hand, samples obtained from the berm environment (see Fig. 4) show dominance of the fine skewed sediment followed by near symmetrical except for location 15, which is characterized by coarse skewed curves with value 0.117Ø. The same features (i.e., fine skewed to near-symmetrical) also are noted for the dune environment (see Fig. 4), but in this environment some changes happened at locations 13 and 15. While skewness values show coarse to very fine skewed respectively, the wide range of skewness values from the dune environment along the study area reflect the asymmetry of wind speed and direction. Livingstone et al. (1999) found that the variations in grain-size parameters between dunes are related to the height of the dune vegetation cover.

In general, backshore and dune environments receive their sediment by wind action which is winnowing fine particles from the sea side towards the land side (a direction favored by the prevailing wind) (Mason & Folk, 1958). However, this action gives the dune sediment a positive skewness nature (Mason & Folk, 1958). Furthermore, in the current study, the wind direction is from the sea side towards the land side. At location 4, the sediment shows an extreme value (very coarse skewed), which is due to the presence of two modes (sand and silt) with good content of coarse and very fine sand (polymodal). Therefore, the sediment in this area is very poorly sorted. Friedman (1967) has found that where fines exceed the energy needed for transport, the beach sediment are deposited from suspension. In other words, most fines imported to the beach area are in suspension mode on the breaking zone due to the uplifting force caused by the waves. These fines are washed towards the onshore side, whereas sand is transported towards the offshore side. When the supply of fines exceeds the wash energy, some fines are transported towards the offshore and settle as muddy sand. The supply rate and beach processes are mainly associated with seasonal changes. 4.1.4. Kurtosis (KG) Kurtosis is a measure of the tailedness of the grain size distribution. It is also similar to sorting in showing dominance of the center or ends of the population (Cadican, 1961). The average kurtosis value (1.09Ø) from the foreshore environment (see Fig. 5) indicates a mesokurtic condition. It is also noticed that, the average value from the southern sector shows leptokurtic, while this value changes to mesokurtic conditions in the northern sector. The average values from berm and dune environments (1.15Ø and 1.11Ø respectively) show leptokurtic conditions. The berm as a whole shows dominance of leptokurtic conditions followed by mesokurtic conditions, whereas just two locations are showing platykurtic conditions (Locations 7 and 10). In the dune environment, the leptokurtic condition is dominant in the southern sector except for Location 1, which shows a platykurtic conditions, while the northern sector shows dominance of mesokurtic conditions except for Location 13 which shows platykurtic conditions. Sorting of sediment in high or low energy environments shows extreme values of kurtosis (Folk & Ward, 1957). According to this, sediment from the beach environment with high energy and high sorting rate show extreme kurtosis values (leptokurtic to very leptokurtic).

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Fig. 4. Skewness from foreshore, berm, and dune environments along the study area. (note: Vcsk: Very coarse skewness, Csk: Coarse skewness, Nsy: Near symmetrical, Fsk: Fine skewness, and Vfsk: Very fine skewness).

Fig. 5. Kurtosis from foreshore, berm, and dune environments along the study area (note: Vpk: Very platykurtic, Pk: Platykurtic, Mk: Mesokurtic, Lk: Leptokurtic, and Vlk: Very leptokurtic).

Poorly sorted sediment usual shows platykurtic kurtosis with coarse and fine ends of the population represented over.

4.2. Distribution of heavy mineral concentrations 4.2.1. Foreshore Heavy minerals (HM) weight percentage (WT%) from the foreshore shows big variations between the þ60 and þ230 fractions. As listed in Table 2, the percentage of HM from þ60 ranges from 0.038 to 16.40% (average 3.53%) and the long shore distribution shows stabilization with some exceptions at locations 2, 5 and 15 (see Fig. 6), where the increase is due to the particular conditions at a site such as extra supply of heavy fractions. In the fine fraction, the values of HM WT% take the range from 3.124 to 45.67% with an average of 12.43%. As presented in coarse fractions, the distribution histogram of fine heavy minerals shows stability in the distribution (see Fig. 7). On the other hand, the total heavy minerals (THM) percentage for the bulk samples from the foreshore ranges from 1.56 to 23.65% (average 6.4%). Moreover, it seems obvious that the content of heavy minerals in the study area increases from the southern to the northern sector (see Fig. 8). This indicates the high efficiency of rivers in the northern sector to transfer and deposit heavy mineral

grains. Fig. 9 shows the spatial distribution of heavy minerals in foreshore sediment along the study area. However, the content of THM% at most locations is less than 5%. The major heavy minerals in the coarse fraction are ilmenite (6.23e37.85%), garnet (12.12e48.13%), sillimanite (7.31e39.47%), magnetite (0e32.83%), rutile (0e5.56%), monazite (0e3%), and zircon (0e2.04%). Fig. 10a shows the irregular distribution of the major heavy minerals in the coarse fraction along the coastal part of the study area, in which the garnet, ilmenite, and sillimanite (among others) have the highest concentrations. In the þ230 fraction, the distribution of the major heavy minerals has more regularity (see Fig. 11a), where sillimanite, magnetite, ilmenite, and garnet have the highest concentrations. Magnetite and sillimanite in the fine fraction show an inverse relation. In general, the magnetite is a common accessory mineral in igneous rocks, whereas the sillimanite is common in high grade gneiss, which indicates the multiple-sources of the sediment in the study area.

4.2.2. Berm The weight percentage of heavy minerals for the bulk sediment in the berm sediment along the study area ranges from 2.18 to 51.84%, with an average of 23.28%. Fig. 12 shows the spatial

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Table 2 Distribution of heavy minerals (WT%) in the study area (note: Min. ¼ minimum, Max. ¼ maximum; Av. ¼ average). Location

Environment Foreshore

L1 L2 L3 L4 L5 L6 L7 L8 L9 L10 L11 L12 L13 L14 L15 Min. Max. Av.

Berm

Dune

þ60

60 to þ230

THM%

þ60

60 to þ230

THM%

þ60

60 to þ230

THM%

0.52 8.934 0.214 0.18 11.842 0.588 0.038 4.132 0.818 0.45 1.992 0.294 1.366 5.246 16.406 0.038 16.406 3.53

4.268 15.1 6.614 3.15 24.23 4.656 3.124 4.898 6.0118 10.572 5.68 5.742 29.08 17.79 45.668 3.124 45.668 12.43

2.16 7.99 3.31 1.58 12.7 2.35 1.56 2.65 3.09 5.3 2.93 2.88 14.6 9.15 23.65 1.56 23.65 6.4

0.254 7.222 0.326 0.428 16.028 2.61 5.778 37.132 9.332 37.39 2.954 1.706 12.464 0.428 62.234 0.254 62.234 13.085

9.662 23.68 12.492 4.322 22.462 8.394 84.752 42.386 73.354 85.862 16.34 11.94 88.856 91.506 97.466 4.322 97.466 44.9

4.84 12.20 6.26 2.18 12.03 4.27 42.66 23.05 37.15 44.80 8.32 6.06 45.05 48.41 51.84 2.18 51.84 23.28

0.27 e 0.36 0.514 0.198 1.63 2.986 e e 28.836 3.224 15.87 5.606 e 3.414 0.198 28.836 5.72

9.13 e 11.628 7.534 7.574 9.722 14.11 e e 59.958 34.356 34.036 77.584 e 33.38 7.534 77.584 27.18

4.58 e 5.83 3.79 3.8 4.93 8.7 e e 31.42 17.34 17.81 39.07 e 16.86 3.79 39.07 14.01

Fig. 6. Distribution of heavy minerals WT% in the þ60 fraction.

distribution of heavy minerals in the berm sediment along the study area. It shows that the berm sediment along the study area has relatively high concentrations of heavy minerals. In the þ60 fraction, the heavy minerals percentage shows a relatively high percentage of HM in the northern sector, where it achieves the highest value at Location 15. Some abnormality happened in Gosthani River Estuary which can be explained by excess supply of the fine fraction compared to coarse particles The abnormal value at Location 15 (north of Bhimunipatnam) is the result of two factors working together to achieve this high concentration. The first factor is the near shore currents, which transport the heavy mineral rich sand from the Gosthani River Estuary (these currents have southnorth direction). The second factor is the high waves regime, which transport and concentrate the heavy minerals at the berm point with its forward and backward movements. In the fine fraction (þ230), the HM WT% values range from 4.322 to 97.46%, with an average of 44.9%. The distribution histogram within the fine fraction corresponds with the distribution in the coarse fraction with some change in Gosthani River Estuary. This indicates that the coastal area is receiving more of heavy minerals as fine particles. The distribution of the major minerals from the berm sediment along the study area demonstrates the high percentage of garnet

within the coarse fraction which achieves 74.36% at Location 7. The distribution also shows the gradual increase in the magnetite percentage towards the north, where the highest percentage in the Gosthani River Estuary exceeds 50%. The percentage of sillimanite shows a decrease towards the north. From that it can be concluded there are different sources of sediment in the study area. In the finer fraction, Fig. 11b clearly confirms the aforementioned spatial distribution, where the highest percentage of magnetite was obtained in the northern sector at Location 15 (78.69%). On the other side (southern sector), the sillimanite minerals were marked as the dominant minerals with 56.58% at Location 1. Other minerals were characterized by steady ratios along the study area, with some variations in the garnet percentage towards the north, where the percentage reached 2% at Location 15. Zircon and monazite minerals were found in promising quantities for economic use, especially on the two sides of the Gosthani River Estuary.

4.2.3. Dune The weight percentage of heavy minerals in the bulk sediment from the dune environments ranges from 3.79 to 39.07%, with an average 14.01% (see Fig. 13). This percentage has a range from 0.198 to 28.83% in the coarse fraction, with an average of 5.72%. In the

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Fig. 7. Distribution of heavy mineral WT% in the þ230 fraction.

finer fraction, the weight percentage increases up to 27.18% as an average, and the range varies from 7.53 to 77.58%. Garnet, sillimanite and ilmenite are the dominant heavy minerals in the coarse fraction (see Fig. 10c). While in the fine fraction, magnetite has the highest percentage among the other heavy minerals along the study area as shown in Fig. 11c, followed by sillimanite and garnet. Ilmenite in the fine fraction has steadily increased from the southern sector towards the north where it achieves the highest percentage in Location 15 (30.86%). 4.3. Total heavy minerals distribution in the study area Matching between the heavy minerals distribution and the mean grain size of sediment from different environments is very helpful to understand how the interrelation and the effect of medium processes (Reddy et al., 2007). These processes play a major role in the sediment selectivity depending on specific gravity and the shape of the grains. The total heavy minerals distribution charts clearly show that the THM% in the coarse fractions from the berm environment have a relatively high percentage compared to other environments. This percentage increases from south towards north, where it achieves the highest value at Location 15 (about 63%), which might be explained because of the near shore currents that have the same direction (Chandramohan et al., 1984). In addition to

that, the rate of supply by local streams plays a major role on the concentration and size of the heavy minerals fraction, which can be noticeable at Locations 9, 10, and 11, where the supply agents in these locations are small seasonal streams. In dunes, the distribution of coarse heavy minerals fractions is associated with many factors, such as wind direction, coastal geomorphology, dune height, and vegetation cover (Sloss et al., 2012). In the total heavy mineral distribution chart (Fig. 8), the THM% shows relatively high concentrations in the northern sector compared to the same percentage in the southern sector of the study area. The previously mentioned factors are found at Location 11 in the northern sector. In addition to the rate of supply, the percentage of heavy minerals in the foreshore environment is directly affected by waves and tidal currents (Reddy et al., 2012). In the study area, the HM WT% of the coarse fraction shows low concentrations at most locations, which is due to the repeated wear and tear by wave action. On the other hand, results obtained from the Sarada and Gosthani river estuaries reveal that the supply rate of coarse heavy mineral fractions is more than the wash rate. Fine fractions from the berm environment show a high concentration of HM WT% (average 49.83%). This percentage clearly shows an increase in the HM content from south towards north along the study area. In general, fine fractions are more likely to be transported from the source than coarse fractions and also within

Fig. 8. Total heavy minerals distribution in the study area.

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Fig. 9. Spatial distribution of the heavy minerals in the foreshore sediment along the study area.

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Fig. 10. Distribution of major heavy minerals in the coarse fraction (þ60), a) foreshore, b) berm, and c) dune (note: Il ¼ ilmenite, Rut ¼ rutile, Mon ¼ monazite, Gar ¼ garnet, Zir ¼ zircon, Sil ¼ sillimanite, Mag ¼ magnetite).

Fig. 11. Distribution of major heavy minerals in the fine fraction (þ230), a) Foreshore, b) Berm, and c) Dune (note: Il ¼ ilmenite, Rut ¼ rutile, Mon ¼ monazite, Gar ¼ garnet, Zir ¼ zircon, Sil ¼ sillimanite, Mag ¼ magnetite).

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Fig. 12. Spatial distribution of heavy minerals in the berm sediment along the study area.

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Fig. 13. Spatial distribution of heavy minerals in the dune sediment along the study area.

A. Mohammad et al. / International Journal of Sediment Research 35 (2020) 484e503 Table 3 Surface textures types used in this study. Mechanical origin

Chemical origin

     

     

Collision pits (small, medium and large) Conchoidal fractures Straight steps Arcuate steps Upturned plates Parallel striations

Solution pits and hollows Solution crevasses Irregular surface solution Surface polishing Crystalline overgrowth Chemical etch pits

 Imbricated grinding features

Mechanical/chemical origin

     

    

Bulbous edges Straight scratches Curved scratches Sub-angular outline Rounded outline V-shaped patterns

Fracture plates/planes Low relief Medium relief High relief Adhering particles

the deposition area, which has been found by many researchers (such as, Azam et al., 2001; Borreswar Rao, 1957; Cheepurupalli et al., 2012; Dill, 1998; Komar & Wang, 1984; Mahadevan & Nateswara Rao, 1950; Philander et al., 1999; Sunita et al., 2018; among others). The selective property and settling velocity are considered as the major factors in fine grain-enrichment (Slingerland, 1977, 1984). Komar and Wang (1984) found that, “the degree of concentration of minerals in the placer deal with increasing grain density and decreasing size”. This point of view explains the high concentration of ilmenite in the fine fraction along the study area. Fine-heavy fractions from the dune environment show correlation with the same fraction in the berm environment, which can be attributed to the fact that the berm is the main source of the fine fractions, whereas the rolling over or windblown sand are the transport-supply for the dune area. In the foreshore environment, as in the coarse fraction, the concentration of THM% in the fine fraction shows low values, which reinforces the wave-wash theory for selective minerals. 4.4. Surface microtextures of heavy minerals Provenance studies of heavy minerals have been undertaken by numerous researchers (such as, Callender & Folk, 1958; Dill, 1998, 2007; Dill et al., 2007; Feo-Codecido, 1956; Gravenor, 1979; Hubert, 1962; Krynine, 1946; Morton, 1985, 1991; Morton &

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Hallsworth, 1999; Statteger, 1987; among others). The microtexture of the heavy mineral grains has been utilized as an indicator to understand the transport history, processes, and depositional environments. The grain-surface studies of quartz have been an investigation area for Krinsley and Donahue (1968), Krinsley and Doornkamp (1973), and Le Ribault (1975). These earlier studies provided good information about the mechanical and chemical actions affecting the grain surface, in addition to their use as an environmental indicator. SEM is probably the most useful auxiliary instrument (Dill, 2007; Krinsley & Donahue, 1968; Vos et al., 2014) to identify surface microtexture and grain morphology at the micron scale. The microtexture of (heavy and/or light) mineral grains have been divided into three types depending on their formation origin (Krinsley & Donahue, 1968). These types are of mechanical, chemical, and mechanical/chemical origins as listed in Table 3. The surface textures present on the heavy-mineral grains have been analyzed. The heavy mineral grains have been selected from four locations in the study area. These locations are the Sarada River Estuary, Yarada Beach, Lawsons Bay, and the Gosthani River Estuary (Locations 2,7,9, and 14, respectively). Twenty-two features have been identified; where thirteen features are of mechanical origin, four are of chemical origin, and five features have been formed as a result of interaction between chemical and mechanical processes. 4.4.1. Sarada River Estuary (Location 2) The heavy minerals that were studied in the Sarada River Estuary (monazite, ilmenite, rutile, and kyanite) show the dominance of mechanical features (Table 4). This result indicates that the grains have been transported for a long distance, where the rounded outlines and collision pits are the main and most observed features on the grain surface (see Fig. 14). Chemical features have less impact on these grains since they are present as small chemical pits and some solution hollows as on the rutile grain (see Fig. 14b). In addition to that, some adhering particles have been observed on the monazite surface. 4.4.2. Yarada Beach (Location 7) Heavy mineral grains that were obtained from Yarada Beach seem to be highly affected by chemical processes (Table 4). The solution hollows and the solution pits are the dominant features on the grains surface. On the other hand, mechanical processes have left their own prints as the rounded outlines, small impact pits, conchoidal fractures, and scratches which can be noticeable on the garnet, rutile, and zircon grains (Fig. 15). Yarada Beach is considered

Table 4 Identified microtextures, and their abundance, on heavy mineral grains from the study area. Location name (Number)

Heavy minerals

Mechanical origina

Mechanical/chemical origina

Chemical origina

Sarada River Estuary (2)

Monazite Ilmenite Rutile Kyanite Garnet Rutile Zircon Ilmenite Zircon Rutile Ilmenite Garnet Ilmenite Garnet Zircon Monazite

AA B AA AA AA B C AA B A AA AA A B B A

B D D C D D AB D C D C AB B C B C

B A A D A AA A C C C C B B AA A B

Yarada Beach (7)

Lawsons Bay (9)

Gosthani River Estuary (14)

a

Note: AA: very abundant (>75%), A: Abundant (75e50%), B: Common (50e25%), C: Present (25e5%), D: Rare (<5%), AB: Absent.

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Fig. 14. Surface microtextures of heavy minerals from the Sarada River Estuary. a): Sub-rounded monazite grain shows small pits, (a) adhering particles, and (b) curved scratches. b): Rounded ilmenite grain with (a) small pits and solution pits. c): Rutile grain shows angular shape with some rounded edges and numerous conchoidal fractures, upturned plates, and V-shaped pits. d): Kyanite grain shows elongated-angular shape with (a) collision pits, arcuate steps, and (b) straight steps.

as an erosional area through various seasons (Ganesan & Raju, 2010). This allows the chemical weathering to take place, in addition to that, the circular motion of sediment due to waves action is the main reason for the mechanical features on these grains surfaces.

4.4.3. Lawsons Bay (Location 9) The studied heavy minerals from Lawsons Bay are zircon, rutile, ilmenite, and garnet. This area receives its sediment from small channels pouring into the Bay of Bengal. The microtextures of the grains show dominance of mechanical processes (Table 4), where all the grains are characterized by rounded outlines reflecting sediment reworked by waves. Zircon grains (see Fig. 16a) are characterized by large conchoidal fractures, linear steps, and small impact pits on the surface. These features are due to grain-to-grain impacts (Higgs, 1979), mechanical grinding, or abrasion (Finzel, 2017). Ilmenite grains show spherical shape (Fig. 16c) with numerous etch pits. Stieglitz and Rothwell (1978) found that the microtextures of some minerals depend on crystallography and also on the chemical conditions of the depositional environments.

This finding leads to the conclusion that the spherical form is due to the trigonal system of ilmenite minerals. Garnet grains show irregular shapes with dissolution features, such as surface pitting, linear steps, and also numerous straight scratches which reflect a combination of chemical and mechanical processes. Margolis (1968) studied numerous quartz grains from different environments. He found that the grains under low wave activity are highly impacted by sea water which is why they exhibit oriented etch pits. On the other hand, gains from moderate wave regimes show both chemical and mechanical features, where the mechanical textures are a result of grain to grain impacts (Krinsley & Takahashi, 1962).

4.4.4. Gosthani River Estuary (Location 14) Ilmenite, garnet, zircon, and monazite are the studied heavy minerals from the Gosthani River Estuary area. Ilmenite grains (see Fig. 17a) show well rounded shapes with flake features on the grain surface. The mechanical feature is present as linear steps, and this might lead to the conclusion that the grain was under diagenesis conditions for a long time. Angular garnet grains (see Fig. 17b) show many chemical and mechanical features, where the solution pits

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are the main chemical feature while mechanical ones are present as impact V-shaped pits and linear and arcuate steps. Garnet grains show overgrowth features on the grain surface and also within hollows. Zircon grains (see Fig. 17c) show numerous etch pits in addition to solution hollows. Well-rounded outlines suggest that the grains have been transported for a long distance, while these grains were not subjected to beach processes yet. Monazite grains (Fig. 17d) show similar features to zircon grains, where etch pits and solution hollows are the major features on the grain surface. In addition to this, the conchoidal fractures are present as mechanical features. 5. Summary and conclusions Studying the grain size statistics and heavy minerals of the sandy samples have been taken from three sub-environments, namely, foreshore, berm, and dune in the area between the Sarada and Gosthani Rivers of the Visakhapatnam coast of India. The

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results of the analysis demonstrate a relation between the grain size and heavy minerals concentration. The sediment grain size in the study area directly affects the concentration of heavy minerals, in addition to marine and Aeolian processes which play major roles, either in enrichment, or in decreasing the concentration after deposition (Komar & Wang, 1984). Most of the sediment shows medium to fine grain sizes, where the coarse grains exist in low ratios which suggests a low energy environment of transport and deposition. The sorting ranges between moderately well sorted to well sorted. The good quality of sorting indicates that the sediment was deposited under high energy (Biju Sabastian et al., 2002). Heavy minerals along the study area showed increasing concentrations from south to north following the near shore currents direction. These heavy minerals might have been derived from metamorphic rocks (khondalites and charnokites) from the Eastern Ghat. The spatial distribution of ilmenite, magnetite, zircon, garnet, sillimanite, rutile, and monazite suggest that grain size, settling

Fig. 15. Surface microtextures of heavy minerals from Yarada Beach. a): Garnet grain shows sub-angular surface with rounded edges, this grain shows (a) conchoidal fractures, (b) straight scratches and big size curves. b): sub-rounded rutile grain shows big chemical hole and crystals growth (white arrow), and medium pits. c): Sub-rounded zircon grain shows (a) straight grooves and (b) reworked conchoidal fractures. d): Rounded ilmenite with numerous small pits and chemical solution.

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Fig. 16. Surface microtextures of heavy minerals from Lawsons Bay. a): Large conchoidal fracture on an angular zircon grain with high relief. b): elongated rutile grain with big pit (white arrow) and reworked conchoidal fractures. c): Rounded ilmenite grain with small pits. d): Angular garnet grain with conchoidal fractures and straight scratches.

velocity, and specific gravity have played important roles in their concentration in every environment. Most heavy minerals in the current study are associated with the grain size of the sediment. The weight percentage (WT%) of ilmenite, sillimanite and zircon increases with decreasing grain size, whereas the WT% of garnet is more concentrated in the coarse fractions. The dune and berm sediment present on the two sides of the Gosthani River Estuary contain economic amounts of heavy minerals such as magnetite, ilmenite, zircon, and monazite, which can be considered as potential reservoirs for mining in the future. In contrast, the Sarada River Estuary sediment showed low concentrations of economic heavy minerals.

Grain microtextures of heavy minerals from The Sarada and Gosthani river estuaries show the dominance of mechanical features, where the conchoidal fractures, impact pits, and linear and arcuate steps are the most commonly observed features on the grain surfaces, in addition to well-rounded outlines. All these features indicate that the grains have been subjected to long distance transportation. Grains from the beach areas (Yarada and Lawsons Bay, Locations 7 and 9, respectively) show a combination of mechanical and chemical features. These features reflect the environmental energy and conditions, where all of these microtextures indicate moderate to high wave energy. The microtextures which have been recognized in the current study do not seem detailed

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Fig. 17. Surface microtextures of heavy minerals from the Gosthani River Estuary. a): Ilmenite grain shows rounded shape with flakes features on the surface and straight steps (white arrow). b): Angular garnet grain shows crystalline overgrowth (white arrow), chemical solution and V-shaped pits. c): Sub-rounded zircon grain shows solution hole (white arrow) and big and small pits. d): Sub-rounded monazite grain shows solution pits (white arrow) and reworked conchoidal fractures.

enough to determine the environmental conditions, such as provenance, transport agents, and depositional processes.

Acknowledgments This research did not receive any financial support from any governmental or private agency. All costs were provided by the author. The author would like to thank Dr. Mai Mohamad and Mr. Rambabu Ravuri for valuable recommendations.

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