REE geochemistry of recent clastic sediments from the Kaveri floodplains, Southern India: implication to source area weathering and sedimentary processes

Abstract

The Kaveri River drains through Archean gneissic and charnockitic terranes in south India. The rare earth element (REE) chemistry of the floodplain sediments, along with their major and trace element composition in different size fractions, are discussed. We observe a strong coherence between REE and TiO₂ contents in the sediments, which is suggestive of strong control by titanite, or its weathered products, on the REE chemistry. REE concentrations also show a general increase with decreasing size of bulk sediments, different size fractions and of light and heavy mineral fractions. This suggests the presence of REE in the Fe-oxy-hydroxide surface coatings on clastic grains, formed by the weathering of hornblende and titanite in the granodioritic to dioritic protoliths. We also interpret the data as showing that REE patterns of clastic sediments, notably Eu anomaly, are affected by the degree of source rock weathering, as well as by the fluvial processes of sorting and mineral differentiation. Therefore, for provenance study, sediments having all granulometric grades, such as the floodplain sediments, are preferable because they most closely represent the source, particularly when the source region suffered little chemical weathering. In the present case, the sediments were derived from the high standing hills of Archean charnockites because of their recent uplift and physical denudation.