Geochemistry of estuarine sediments from Marakkanam area, Tamil Nadu, India: source area weathering and provenance implications

In the present study, 135 cm and 125 cm sediment cores were collected from Yedayanthittu estuary at a water depth of 1 m to infer the provenance and paleoweathering conditions of the source rocks. The core samples were carbon-dated and analyzed for calcium carbonate, organic matter, and major oxides to decipher the sea level changes, source area weathering, and provenance. The calcium carbonate is chiefly derived from terrestrial and coastal input into the mangrove ecosystem, and the rapid increase of calcium carbonate percentage at certain levels of the cores is due to enrichment of shell fragment. The organic matter content of the sediments is mostly derived from terrestrial input and mangrove debris. Geochronological studies indicate that the sediments deposited during early Holocene period with an average sedimentation rate of 0.015 cm/y −1 . The 14 C dates and Holocene sea level curve suggest the gradual and slow sea level rise along the study area. The chemical index of alteration (CIA), plagioclage index of alteration (PIA), and A-CN-K diagram reveal that the source rocks were subjected from low to moderate intensity of chemical weathering. The index of chemical variability (ICV) values indicates that the sediments are immature to moderately mature in nature. Major oxide concentrations of core sediments indicate that they were derived mainly from recycled felsic source rocks.