Unravelling the quaternary palaeoglacial archives from the Trans-Himalaya: Evidence from geomorphological, sedimentological studies and luminescence dating in Spiti basin, NW Himalaya

Several studies have been attempted in the rain-shadow zone of the NW Indian Trans-Himalaya to delineate quaternary spatio-temporal palaeo-glacial extents. The glaciers in this region are influenced by two major climatic systems; i.e. Western Disturbances (WD) and Indian Summer Monsoon (ISM) with spatio-temporal variable intensities from north to south respectively. In case of the transitional climatic zones, on the southern fringe of the Trans-Himalaya where ISM and WD both have been instrumental in controlling the glacial activity, there has been wide range of study conducted in Lahaul and Zanskar. Spiti, further E-SE, though lacks palaeo-glacial studies due to poor glacial deposit preservation and dominant fluvial recycling of sediments, despite glaciers currently supplying over 50% of the basin's water.  Although, modern glaciation in Spiti is limited to high altitudes above 5000m, features like glacial striations, U-shaped valleys, and sparsely preserved palaeo-glacial deposits in various parts of Spiti indicate that glaciers once extended to much lower elevations in the past.

Our work focused on spatio-temporally constraining these palaeo-glaciations within Spiti. Our study involved detailed geomorphological and sedimentological studies using litho-facies and clast-macrofabric analyses to identify the palaeoglacial deposits and past glacial extensions within the basin. The identified deposits were chronologically constrained using luminescence dating in order to understand temporal glacial landscape evolution within Spiti. Our study identified the dominant LGM influence on the glaciation on the S-SW side of Spiti trunk channel towards southern fringe of Trans-Himalaya between ~29 ka to ~15 ka. Whereas the palaeoglacial signatures in the northern direction of trunk channel of Spiti towards Ladakh are majorly constrained between ~100 ka – ~45 ka. Our findings indicate that paraglacial processes were the primary driver of landscape evolution in the upper Spiti basin during the late Quaternary, leading to the basin's headward expansion.