Characterization of sedimentary environment, provenance and distribution of heavy minerals along the Tamil Nadu shoreline, East coast of India

Abstract

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.