Holocene Evolution of the Palar River, Southern India: Evidence for Channel Migration, Provenance Shifts, Weathering Processes, and Tectonic Controls

 

The present study examines the catchment and source morphodynamics of the Palar River, southern Peninsular India. A multidisciplinary approach—remote sensing techniques, lineament analysis, geochemistry, and ground-penetration radar (GPR)—was applied to better understand its evolution during the Holocene. The major lineaments in the Palar River basin predominantly show a NE–SW trend. Five major faults have been identified in the basin, including a transition zone where frequent low-magnitude earthquakes have occurred. The major fault F1, a strike-slip fault, occurs in the upper reaches of the Palar River and follows a NE–SW trend. Other major faults, F2 and F3, are also associated with a transition zone where frequent minor and major tremors have been documented. Fault F4 runs parallel to the Cheyyar River, and significant changes in the river course have resulted from movement along these strike-slip faults. Fault F5, located nearer to the east coast, indicates a passive tectonic activity regime. The after-effects of tectonic activity in the basin are further evident from the GPR profiles.

Sediments of the active Palar River are dominantly litharenite, arkose, and wacke, whereas the paleochannel sediments are predominantly shale. Weathering proxies such as the Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), elemental ratios, and the A–CN–K plot indicate intense post-depositional weathering of the paleochannel sediments due to climatic variability. In contrast, due to ongoing tectonic activity in the source region along with subsequent aggradation and degradation in the fluvial regime, sediments of the active Palar River exhibit low to moderate weathering.

Geochemical data further reveal that sediments from the active Palar River and the paleochannels are predominantly derived from active continental margin and passive continental margin settings, respectively. Major oxides, trace elements, and rare earth element (REE) data indicate that the Palar River sediments are derived from felsic sources, whereas the paleochannel sediments originate from mafic sources. Overall, the study suggests that the catchment area of the Palar River shifted southward during the Holocene due to tectonic uplift. Subsequently, the paleochannel sediments underwent post-depositional weathering. Ongoing tectonic activity combined with monsoonal variability has enhanced rapid erosion in the catchment, resulting in the deposition of thick sediment sequences from the middle to lower reaches of the active Palar River.