No abstract

No abstract

The present-day Palar River and its palaeochannel located in the Southern Peninsular India were investigated with a multidisciplinary approach. The main aim of the study was to reconstruct the palaeoenvironment history of the Palar River basin and to delineate the role of Holocene fluctuations that played a major role in the geomorphological evolution of the region since the Holocene period. The results obtained based on sedimentary facies analysis supported by elemental concentrations and optically stimulated luminescence (OSL) dates reveal distinct seven climatic phases since the past ~10 ka. Phase 1 signifies a very high precipitation as attested by the low CWI with high Rb/Sr ratio. Subsequent to Phase 1, a decreasing trend in the northeast monsoon rainfall (NEMR) is observed (Phase 2). Phase 3 (~4.83–3.59 ka) reflects a decrease in NEMR further supported by low Mn/Al, Mg/Al and Chemical Index of Alteration (CIA) values. Phase 4 (~3.59 ka) is marked by high sand flux, higher K/Al, Ti/Al, Rb/Sr and Ba/Sr ratios coupled with lower values of CaO/MgO, Mn/Al and Fe/Al indicating wetter conditions in the catchment area resulting in the intense weathering of the bedrocks caused owing to the increase in NEMR precipitation. Phase 5 (3.26–2.42 ka) reveals a decline in NEMR precipitation coupled with rapid upstream avulsion because of neotectonic activity that occurred in an intense dry phase. Phase 6 (~1.88–1.44 ka) is marked by an augment NEMR causing higher K/Al, Mg/Al, Ti/Al ratios, CIA and CWI values. Finally, Phase 7 (~1.44 ka–present) is marked by lowered elemental solubility and mobility reflecting short periods of weaker or deteriorated NEMR. The documented record of the Palar River and palaeochannels suggests Holocene NEMR variability in the study region and is synchronous with the various proxy records of NEMR-dominated regions, however, revealing an inverse coupling with southwest monsoon rainfall (SWMR) during the Holocene period.

No abstract

This present study describes the geochemistry of fluvial sediments of the Palar river (lower reaches), Southern Peninsular India, with an aim to evaluate their provenance, weathering and tectonic setting. The bulk sediment chemistry is influenced by grain size. The river sediments are enriched with SiO2 and depleted in Al2O3, K2O, CaO, Na2O, MgO, P2O5, MnO, Fe2O3 as compared with UCC values. Geochemical classification indicate that the sediments are mainly arkose, wacke and shale in composition. Discriminant diagrams together with immobile element ratio plots reveal that, the Palar river sediments are mostly derived from rocks formed in an active continental margin. Additionally, the rare earth element ratios as well as chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomalies indicate felsic rock sources. The chemical indices of alteration suggest that Palar river sediments are chemically immature and have experienced low chemical weathering effects. This is further supported by the Th/U Rb/Sr ratio and A-CN-K ternary diagram, with most of the sample data points falling close to the plagioclase-smectite line. The bivariate plot of Th/Sc versus Zr/Sc suggest a moderate recycled origin of the sediments.