Indian Journal of Geo - Marine Science Vol. 45 (2), February 2016, pp. 191-196 Microtextures on quartz grains in the beach sediments of a high energy regime, , Southwest coast of Silpa.B.L1, Reji Srinivas1*, Likhil.A.C2, Aneesh T.D1, Krishna Prasad1 & Sajan K2

1National Centre for Earth Science Studies, Earth System Science Organisation, Ministry of Earth Sciences - 695011, India

2Department of Marine Geology and Geophysics, School of Marine Sciences, Cochin University of Science and Technology, Cochin -682016, India

[Email: [email protected]]

Received 28 October 2015 ; revised 7 December 2015

Micro textures of the quartz grains in the beach sediments of Poovar- coastal stretch have been studied to decipher the variations in the morphology and the processes responsible. Open beaches and the seawall dominated region indicate the influence of both chemical and mechanical processes. The quartz grains from tidal inlets show the dominance of chemical features than mechanical features whereas the dominance of mechanical features is observed in pocket beaches. Chemical factory ( Titanium Limited) at Veli forms a major reason for the occurrence of abundant chemical features. Sediments in open beaches and seawall dominated region undergoes either longshore or crosshore transportation. Besides the longshore drift, the sediments in the tidal inlets were transported to the area by fluvial and aeolian processes and subsequently deposited in the marine environment. Sediments in the pocket beaches divulge the winnowing action existing in the high energy regime.

[Keywords: Microtexture, Morphology, Beach Sediments, Energy regime.]

Introduction earlier in the sandy beaches of Kerala6. In addition to this the estuarine quartz grains also Temporal and spatial changes in coastal register a wide spectrum of microtextures7&8. morphological and transportation processes keep Purpose of the study is to investigate the pace with the variations in the hydrodynamic influence of different morphology of a high regime. The most manifest of these processes is energy regime in the quartz grains. the transportation and deposition of sediments along the shoreline. This means that not only the The study area extending Poovar–Varkala sector total flux of sediments, but also their size (80 20' 30"N and 760 53' 10"E - 80 44' 18"N and distribution is controlled by the dynamics of 760 41' 59"E) which is of 60 km length (Fig.1) waves and currents. Thus the energy condition consists of different morphologies. Coastal and the morphology of the coastal environment morphology along the sector has been seem to be reflected in the characteristics of the substantially customized with both the natural sediments1. Microtextural study of quartz grains and artificial structures. The natural is considered as a power full tool in the morphologies include tidal inlets at Poovar, Veli identification of provenance, transportation and Muthalapozhi in which the rivers emptying processes and the digenetic processes of coastal, are , ParvathyputhanAr and fluvial, glacial sediments2,3. The different impact Vamanapuram respectively. Rocky headlands features and the abrasion marks on the quartz are also observed along Vizhinjam- grains during transportation generally record the stretch and a lateritic cliff at Varkala. Here the mechanical or chemical processes and the open beaches (beaches without any structure) knowledge of such physical and chemical include Poovar-Adimalathura stretch (9km), parameters can lead us to the exact Veli-Pudukurichi stretch (18km) and Anjutengu- environmental discrimination. On the basis of the Nedunganda stretch (6km). The artificial microtextures, it is possible to differentiate the structures comprises the construction of particular depositional environments such as breakwaters for fishing harbours at Vizhinjam marine, fluvial, aeolian and glacial4. The wave and Muthalapozhi, seawalls along Kovalam- energy regime along the Kerala coast exhibits Sankumugham (12km) and Thazhampally- distinct patterns, with the highest energy Poothura (2km). Also groins are constructed at observed in Thiruvananthapuram region5. Quartz Panathura (2), Poonthura (8) and Chilakkur (25) grains with varying microtextures were recorded as part of coastal protection.

1* Corresponding author Present address : National Centre for Earth Science Studies, Thiruvananthapuram-695011,Kerala, India

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pre-monsoon season. Approximately 30 g of each sample were soaked with H2O2 solution to remove organic matter and then treated with 30% HCl and stannous chloride solution to dissolve carbonates and to remove iron stains from the quartz grains. The treated samples were sieved at 1/2Ф interval to separate the sand size fraction9. Grains between 250 to 355 microns were hand-picked under a binocular microscope, mounted on stubs, sputter-coated with gold and examined using scanning electron microscope10. SEM photographs of selected grains were taken to illustrate the shape and micro relief features. Results Grain size characteristics along the Poovar- Varkala coastal stretch are furnished in the Table1. The open beaches and the tidal inlets characterizes moderately sorted to moderately well sorted, medium sand to coarse sand with a mean size of 0.80Ф to 1.24Ф. The coarse grains in the foreshore sediments of Poovar (0.80Ф), indicates the presence of river input which is fed by Neyyar river. Sediments here are fine to

Fig.1 Study Area symmetrically skewed and leptokurtic to mesokurtic in nature. The seawall dominated Materials and Methods region characterizes medium sand (1.16Ф) of Foreshore sediments were collected from 10 well sorted, symmetrical and mesokurtic in locations of Poovar- Varkala sector, character. The pocket beach at Mullur which is incorporating different morphologies during between headland and Vizhinjam breakwater

Table 1- Statistical parameters along Poovar-Varkala coast

Locations Mean (Φ) Sorting(Φ) Skewness (Φ) Kurtosis (Φ) Poovar 0.80 0.85 0.14 0.73

Veli 1.24 0.54 0.15 0.98

Thumba 1.13 0.62 -0.02 1.34 Nedunganda 1.19 1.07 -0.05 1.05

Muthalapozhi 1.11 0.63 0.22 1.07 Valiathura 1.16 0.44 0.04 0.93

Mullur 0.36 0.92 0.03 0.71 Kovalam 2.63 0.42 -0.24 1.68 Varkala 2.01 0.39 -0.20 1.58 193 SILPA et al: MICROTEXTURES ON QUARTZ GRAINS IN THE BEACH SEDIMENTS 193

possess coarse sand (0.36Ф) and it is due to the The quartz grains from the pocket beaches of soaring energy condition existing in between the Mullur are sub angular to sub rounded with structures. Sub-bottom topography and the packet of lenses, Vpits and meandering ridges resultant wave energy at Mullur enhance the (Fig.2j, k). Meandering ridges are formed during churning up of sediments which subsequently grain to grain collision in an aeolian results in coarser sand accumulation. But the environment. The pocket beaches of Kovalam pocket beaches of Kovalam possess well sorted possess subrounded to rounded grains with fine grade sediments of 2.63Ф with higher conchoidal fractures, Vpits and adhering percentage of black sands. This presence of finer particles. Rounded nature of grains generally black sands with high specific gravity is due to indicates the high energy zone where the the winnowing action existing in this energy reworked sediments in the beach are subjected to gradient. Further north, the pocket beaches at rigorous wear and tear by strong waves and had Varkala, characterizes moderately well sorted undergone further roundness. Conchoidal sediments of fine size (2.03Ф). Poovar-Varkala fractures are common in the quartz grains of the sector with the highest energy condition is sector, which indicates that the coastal area dominated by medium sand whereas the pocket received more sediment from the crystalline beaches except Mullur are generally source rocks. Whereas in the pocket beaches of characterized by moderately well sorted to well Varkala the grains are subangular to sub rounded sorted, coarsely skewed fine sands which are with conchoidal fractures and Vpits. In the meso to leptokurtic in nature. seawall dominated region at Valiathura, the grains are sub angular to sub rounded with The open beaches and the tidal inlets along the conchoidal fractures, V pits, straight and curved sector exhibit angular to sub angular grains with scratches and etch pits. Straight or curved Vpits, etch pits and adhering particles. Tidal grooves and scratches occur as shallowly inlets at Poovar, Veli and Muthalapozhi possess indented tears on the grain surface (Fig.2l). These grains with bulbous edges where the presence of features are conceivably formed during early Vpits and chemical etches indicates the fluvial transport and weathering and indicates a high origin (Fig. 2a-c). V shaped pits are irregular and energy environment. differ in size and shape and their density can be directly related to the number of straight and Discussion curved scratches. Adhering particles provide The prevalence of high energy in the Poovar- information on the sediment provenance and Varkala sector is supplemented by the steep these may result from the quartz grain itself, or gradient of the nearshore bathymetry and wave from any other particle to which the quartz grain energy conditions11. Sediments are of medium has collided (Fig.2d). The quartz grains at Poovar size indicating a high energy coast12. Angular to showed both types of chemical (dissolution and sub angular features with bulbous edges, Vpits precipitation) features viz, etch pits and silica and chemical etches indicate the fluvial flowers (Fig.2e). The quartz grain from Veli origin13,14. Angular to subangular outlines shows parallel striation and they occur as a series usually occur in high energy environments with of linear or curved marks on the surfaces (Fig.2f). inadequate transportation causing grain breakage Abundant chemical etchings are observed in the without edge rounding15. The features like etch quartz grains of Veli where the chemical factory pits indicates the chemical origin of the sediment (Travancore Titanium Limited) discharges and also its occurrence can be linked to the 16,17 various chemical wastes, mainly H2SO4 (Fig.2g). contact with alkaline fluids, such as seawater . The grains from Muthalapozhi exhibit straight, Quartz grains of Poovar are characterized by arcute scratches and polygonal cracks (Fig.2h). silica flowers and generally, they are formed Dominance of angular to sub angular grains with during post-deposition on the broken surfaces3. conchoidal fractures at Nedunganda (Fig.2i), Features like parallel striations and polygonal which is at the south of Varkala cliff suggests that cracks are observed in the quartz grains of Veli the grains have undergone short transportation and Muthalapozhi respectively. The parallel and rapid deposition representing a calm striations may occur by the movement of sharp environment. This is in the shadow of Varkala edges against the grain involved18, whereas the cliff, making it of lesser wave energy. Moreover, polygonal cracks are usually formed by the the construction of consecutive groins at physical and/or chemical processes19. Chilakkur, which is at the north of Nedunganda, Occurrence of abundant angular grains at has also favored the serene condition. Nedunganda supports a local source rock origin20

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195 SILPA et al: MICROTEXTURES ON QUARTZ GRAINS IN THE BEACH SEDIMENTS 195

Fig. 2 a-l. SEM images of quartz grains showing (a) Subangular grains (b) bulbous edges (c) V pits (d) adhering particles (e) silica flowers (f) parallel striations (g) chemical etches (h) polygonal cracks (i) conchoidal fractures (j) meandering ridges (k) packets of lenses (l) grooves and scratches rocking motion18. Grooves and scratches are which intern agrees with the studies at Northern characteristic of the littoral zone where they are territory of Australia. Sub angular to sub produced by wave action24. rounded grains with packet of lenses, Vpits and meandering ridges are observed in the pocket Conclusion beaches of Mullur. Sub-rounded grain shape with The Poovar-Varkala sector with the highest packet of lenses and the pit like appearance is energy regime is characterized by fine to coarse indicative of post-depositional events21 and the sand depending on varying morphological meandering ridges are characteristics of aeolian conditions. Open beaches and the tidal inlets transportation22. Commonly, the subangular to possess medium to coarse sand, whereas the subrounded grains are formed in the intertidal sediments in the pocket beaches are of fine zones as it requires severe abrasion to round the grained except at Mullur. In Mullur, the sub- particle edges4. The quartz grains in the pocket bottom topography and the resultant wave beaches of Kovalam and Varkala possesses energy, enhance the churning up of sediments conchoidal fractures with Vpits. Blocky which subsequently results in relatively coarser conchoidal fractures are developed due to intense sand accumulation, while the pocket beaches at transportation in the high energy surf zone18. V Kovalam and Varkala possess well sorted fine shaped patterns (Vpits) are the characteristics of grade sediments. Highest percentage of heavy moderate to high energy subaqueous conditions23 minerals at Kovalam is due to the soaring energy and generally occur on less than 50% of the conditions and resultant winnowing action. grains from the fluvial origin and on more than 50% of those from high energy beaches24. The quartz grains in the tidal inlets show the Straight or curved grooves and scratches are dominance of chemical features like silica observed in the seawall dominated area and in flowers and etch pits rather than mechanical general, they are produced during grain-to-grain features. Formation of adhering particles and collisions when a sharp sub-microscopic edge of polygonal cracks in the area can be of either a grain is drawn across the other grain with a mechanical or chemical processes. Numerous

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