Holocene–pleistocene provenance transitions in the Cauvery Delta, South India: Evidence from Sr-Nd isotopes

Abstract

We investigate temporal shifts in sediment provenance through comprehensive ⁸⁷Sr/⁸⁶Sr and εNd₀ analyses of two sediment cores (Uttrangudi and Porayar) from the Cauvery Delta, South India. We assessed the role of weathering intensity and source rock variability and glacial/interglacial climate phases using isotopic signatures. Isotopic data of two cores reveal distinct shifts in provenance between the Late Pleistocene and Holocene periods. Around ∼14 ka BP, the isotopic signatures indicate enhanced contributions from the Dharwar Craton, consistent with more efficient sediment transport from the distant upper catchment when the lower sea level exposed the continental shelf. In contrast, Holocene sediments (upper core sections) reflect a dominant contribution from the Southern Granulite Terrain, driven by intensified Northeast Monsoons. Our data shows that weathering intensity may influence isotopic compositions, with Nd isotopes being particularly sensitive to these post-depositional processes. The Porayar core exhibits an unusual inverse relationship in which finer fractions correspond to less radiogenic εNd₀ values. Our findings underscore the critical influence of source rock variability, Quaternary sea-level fluctuations, and climate-driven weathering intensity on the Sr-Nd isotopic composition of deltaic sediments.