Propagation of Base-Level Signals into an Active Himalayan Catchment: Morpho-Sedimentary and OSL Evidence from the Satluj River Valley

The geomorphic and sedimentological evolution of the dynamic Satluj River basin is understood through a detailed analysis that combines comprehensive morpho-sedimentary mapping, lithofacies analysis, and optically stimulated luminescence (OSL) dating to evaluate the impact of base-level fluctuations. Although the valley is far from the current coastline, evidences of minor changes in base level caused by climate and sea level processes reach deep into the hinterland is clearly seen in such a dynamic mountain catchment of the Himalaya. These changes majorly control river dynamics, sediment transport, and overall landscape evolution. Frequent landslides, temporary channel damming, lake formation, and large fluvio-lacustrine sedimentary successions direct periods of enhanced sediment input and aggradation. Morphotectonic indices and the presence of seismites in these deposits suggest significant tectonic influence on base-level-driven geomorphic responses.

Optical chronology identifies two major aggradation phases: one from about 30 to 24 ka and another from about 17 to 11 ka. During these phases, more sediment was deposited, less material was transported, and the local base level temporarily rose owing to valley damming. In these periods, the landscape was unstable, resulting in numerous mass-wasting events, the creation of dammed palaeolakes, and the preservation of extensive sedimentary records. Subsequent incision stages form strath terraces, vertically incised gorges, offset channels, and modifications in the shape of Quaternary sediments. This indicates that the base level declined again and tectonic activity resumed.

The observed relationship between aggradation-incision cycles, dammed lakes, and tectonically influenced base-level fluctuations demonstrates how climate-driven base-level modifications can be greatly amplified in dynamic mountain belts. The findings suggest that base-level signals connected to sea-level fluctuations may have an indirect impact on sedimentation and geomorphology over significant distances upstream through complex sediment-routing systems. This study adds new constraints on late Quaternary catchment-scale geomorphic adjustment and improves understanding of how sea-level-induced base-level changes interact with tectonics, landslides, and fluvial processes to shape the Himalayan landscape.