Geochemical Characteristics and Paleo Weathering in Sediments of Noyyal River Basin, Tamilnadu – India

A geochemical study of surface sediment samples distributed in the Noyyal River basin in western Tamil Nadu was studied for major oxides, parent rock source, and the extent of weathering. The Al2O3/TiO2 ratio of the samples ranged from (4.5-18) during monsoon and (3.94-32.14) during summer and fell in the category of mafic and intermediate igneous rocks during both seasons. The samples exhibited PIA with an average value of 64.80 during monsoon and 66.36 during summer. CIA values of the samples averaged 61.48 during monsoon and 62.35 during summer. The CIA vs. PIA, CIA vs. K/Na, and CIA vs. Al/Na for the studied samples for both seasons show low to intermediate silicate weathering in almost all locations. ICV values of samples averaged 49 during monsoon and 47 during summer suggesting that rock-forming minerals like plagioclase and alkali-feldspar are more prevalent and fewer clay minerals are present. The Al2O3/TiO2 ratio of the sample locations ranged from (4.5-18) during monsoon with an average of 10.06 and (3.94-32.14) during summer with an average of 9.94. Most of the samples fell in the category of mafic and intermediate igneous rocks during both seasons. The A-CN-K plot shows the weathering tendency towards muscovite and illite, and the A-C-N plot shows the parent rocks' plagioclases are low to intermediately weathered and the sediments gradually reduce albite and are enriched in weathering of anorthite parent material. The A-CNK-FM shows all the sediment samples lying below the feldspar region, indicating garnet and biotite presence.