Geochemistry of Vellayani Lake Sediments: Indicators of Weathering and Provenance

The Vellayani lake, located on the west coast, Kerala, South India, is a natural fresh water lake. In order to understand the source and nature of the sediments; thirteen lake floor sediment samples were collected from the Vellayani lake at different intervals along the S-N transects covering the entire surface area of the lake. Textural studies indicate that lake floor sediments are dominant in sand (55.39%) followed by clay (30.57%) and silt (14.04%) fractions. Coarse components are dominant at the inlet ofthe stream into the lake. The geochemical content of the sediments reveals low SiO2, MnO, CaO, MgO, Na2O, K2O, and P2O5 content while TiO2, Fe2O3 and Al2O3 are high when compared with Post Archean Australian Shale (PAAS) and Upper Continental Crust (UCC) values. SiO2 is high in coarse fractions while Al2O3 is strongly associated with fine sediments. Major oxide contents supported by Rare Earth Element (REE) data reveal a distinct negative Eu anomaly reflecting a dominant cratonic origin of the sediments. Detailed geochemical data indicate a mixed source, predominantly, the lateritic soils, sedimentary and metamorphic bedrocks exposed around the lake and in the catchment area.