Multi-Proxy Reconstruction of Late Quaternary Monsoon Variability and Fluvial Response in the Central Ganga Plain, India: Insights from magnetic, CHNS and geochemistry records.

The Central Ganga Plain (CGP), a key sector of the Indo-Gangetic foreland basin, contains thick, continuous Quaternary alluvial sequences. Its rapidly subsiding basins preserve a high-resolution terrestrial archive, ideal for reconstructing Indian Summer Monsoon (ISM). This study examines sedimentary profiles from distinct river systems in the Central Ganga Plain (CGP) using a multi-proxy framework. A Late Quaternary trench from the Gomti river (26°52′ N, 80°56′ E, Lucknow) and a Holocene section from the Betwa river (25°28′ N, 79°5′ E, Hamirpur). Sediment sample from Lucknow profile were analysed for CHNS, AMS ¹⁴C dating, mineral magnetism, and bulk geochemistry (major, trace, and REE), while those from Hamirpur were analysed using OSL and AMS ¹⁴C dating, alongside CHNS. The established chronology or Lucknow trench, record from ~24 to 3 kyr BP. The CHNS data shows a significant shift at ~20 kyr, marked by high TOC (3.97%) and C/S ratio (~ 300) indicating enhanced organic productivity and freshwater conditions. Concurrent mineral magnetic signatures (χlf, SIRM and ꭓARM) suggest strong detrital input linked to weaker monsoon. This evolving climatic condition is further investigated through bulk geochemistry, (major, trace and REE), which provide critical insights into sediment provenance, weathering regimes, and paleo-hydrological conditions. The chronology for the Hamirpur trench covers from ~800-12000 years BP and the CHNS data provide distinct environmental phases, marked by a sharp peak in TC (3.31%), TOC (1.56%) and C/N ratio (~439), indicating a enhanced terrestrial organic matter preservation in a low-energy, waterlogged setting around ~3000 kyr BP. This integrated high-resolution multiproxy record from the two distinct river systems provides new insights into monsoon variability and sedimentary responses in the Central Ganga Plain during the late Quaternary.