Evaluating the connectivity of the Yamuna and the Sarasvati during the Holocene: Evidence from geochemical provenance of sediment in the Markanda River valley, India

In the northwest Indo-Gangetic plains, the linkage of the Ghaggar-Hakra paleochannel with the Sarasvati River of early Indian literature and the Harappan (or Indus) civilization poses an important case for understanding drainage reorganization and human-landscape interactions. Among the major paleochannels of the Ghaggar-Hakra, sediment provenance studies on the paleo-Sutlej branch show its connectivity with the Sutlej catchment during the Holocene. However, evaluation of the role of fluvial morphodynamics on the Harappan settlements remains restricted because of limited effort to identify drainage reorganization of the paleo-Yamuna and its connectivity to the Ghaggar-Hakra paleochannel. Here we focus on the sediment deposits in the Markanda Valley, upstream of the northernmost purported paleochannel (Y1) of the river Yamuna, to explore the possible connectivity of the Yamuna catchment with the Ghaggar-Hakra paleochannel through Y1. We analyzed sediment samples from fan surfaces, fluvial terraces, and the modern riverbed for trace element and Sr-Nd isotope geochemistry to identify source signatures. Chronology of the samples, available through Singh et al. (2021), shows aggradation of the fan (57.7 ka) and T-1 to T-5 fluvial terraces during 13.1 to 6.0 ka, and deposition of paleoflood sediment during 3.9–3.8 ka. Results of provenance analysis suggest that sediment in the Markanda Valley was primarily derived from the silicate rocks of the Subathu-Dagshai-Kasauli Formations and the Siwalik Group of the Sub-Himalayas, thus implying that the river Yamuna was not connected to the ancient Ghaggar-Hakra river system (the Sarasvati) through the paleochannel Y1 during the Holocene. The Late Holocene sediment in the Ghaggar-Hakra plains (<4.5 ka), like the sediment in the Markanda Valley, was derived from the sub-Himalaya and transported through Y1, whereas the depositional pathway for the older sediment (>4.5 ka), having sources in the Himalayan hinterland, was likely the southernmost paleochannel (Y2) of the Yamuna.