Sediment Characteristics and Heavy Mineral Distribution in Tamiraparani Estuary and Off Tuticorin, Tamil Nadu- SEM Studies (original) (raw)
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The study area Tamiraparani located between latitudes 8° 25΄ and 9° 13΄ N, and longitudes 77° 10΄ to 78° 10΄ E along the southeast coast of India. All samples were collected between Pre-monsoon July, 2003 and Post-monsoon February, 2004. 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. From the SEM studies, it is observed that the grains are sub-angular with various surface solution features, rounded crescent like pits, straight net like sutures; v-shaped pits are noticed in pre and post-monsoon samples. The coarser nature of the grains may be due to the influence of river activities. The weathered surface futures also noticed in few samples. The sediment texture, mineral and SEM studies, clearly indicate that in pre-monsoon the erosional activities are predominant than the post-monsoon. In both the periods, sediments transport was from river and estuary towards the beach and marine. In pre-monsoon, the deposited sediment were transported and shifted due to longshore current action. But, in the post-monsoon period the sediments deposited due to the multi-source like riverine and marine influence is observed.
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The Chinnavilai and Erayumanthurai beach sediments of the Kanyakumari District consist of medium-grained, moderately well-sorted, unimodal, occasionally bimodal, mesokurtic, leptokurtic and platykurtic. The fine skewed and symmetrical nature of sediments implies the prevalence of high and low energy, entailing a mixed distribution of coarse and fine sediments. The washing and backwashing of waves cause the coarser sediments to retainment and entrapped amidst finer sediments. The heavy minerals distribution reflects that the less content in Erayumanthurai samples, whereas the Manavalakurichi, Enayam, Kurumpanai sediments comprise >60%. The oval shape zircon is devoid of inclusions, whereas, the euhedral zircons comprise subhedral inclusions. Distinct fractures in zircons are caused due to transportation by waves and currents. The garnet and zircon grains are well-rounded, implying the source for these sediments are an admixture of medium to high-grade metamorphic rocks, reworked sediments, charnockite, and granite gneisses.
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Placer mineral deposits and their limited occurrence have gathered worldwide attention for researchers and geologists to exploit new areas of deposition. This research aims to know the transportation and depositional environment of sediments, provenance and distribution of heavy minerals between Besant Nagar and Sathurangapattinam in the coastal region of Tamil Nadu (India). The sediment samples are collected for textural analysis, magnetic susceptibility (MS), petrographical and mineralogical (XRD) studies of sediment samples, including the heavy minerals studies. Grain size analysis showed fine to medium-grained sandy sediment with very well to moderately sorting indicate reworking of beach edges accompanied by unimodal to the trimodal distribution of sediment from the riverine and marine environment. Grains are mostly symmetrically skewed with platykurtic to leptokurtic nature, indicating low-to high-energy environment prevailing in the region where the deposition and erosion are equally balanced in the area. Bivariate and one percentile-median (CM) pattern plots indicated that most of the sediment is deposited by beach processes transporting sediment by bottom suspension and rolling. The amounts of magnetic or iron-bearing minerals are high in locations no. 1 (Besant Nagar beach), 5 (Injambakkam beach) and 12 (Tiger cave beach) interpreted using MS studies, whereas the heavy mineral weight percentage is higher in locations no. 11 (Pattipulam beach) and 12 (Tiger cave beach). The correlation plot of Heavy wt% vs MS showed positive correlation and in general plots deciphered that the locations with high wt% (Besant Nagar, Injambakkam and Tiger cave beach) showed higher MS indicating the presence of magnetic minerals and the correlation plot between individual mineral grain count% vs MS explicated that the locations were rich in magnetic minerals like ilmenite, magnetite (opaques) and epidote (medium magnetic). The petrographical study of heavy mineral and XRD analysis revealed that the study area contained a high percentage of opaques, garnet, zircon, rutile, chlorite, sillimanite, hypersthene, hornblende, tourmaline, possibly derived from charnockites, granulite gneiss, migmatites and basic dykes. The overall investigation concludes that the sediments are distributed at various locations by marine processes depositing sediment rich in magnetic and heavy minerals derived from various rock type sources transported by rivers and later driven by longshore currents of oceans flowing from S to N, N to S during different months and SW-NE monsoon play a vital role in the distribution of beach placers.
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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 (hypersthene) 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 NEeSW configuration and wave energy conditions must have contributed to the formation of heavy minerals in a particular zone.
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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.