Nature, genesis and provenance of silt pellets on the ice surface of Glacier No. 1, upper Urumqi River, Tian Shan, Northwestern China

This paper reports silt pellets found at the terminus of the east branch of Glacier No. 1, Tian Shan, Northwestern China. These pellets of approximately 1 mm in diameter appeared as layers on glacier surface. Two pellet samples were collected for microscope examination, grain-size measurement, and geochemical analysis to understand their nature, origin and provenance. Observations of thin sections show that the pellet is comprised of an inner structureless core and an outer concentric thin layer, explained by a two-stage process: a nucleus-forming stage and a concentric growth stage. The pellet is mainly comprised of poorly sorted (σ = 1.7–1.8) silts (mean grain grain-size = 6.2–6.5 φ) with quartz, feldspar, biotite, pyroxenes, clay, and other minerals. The chemical compositions of the silt and clay portions are very similar to that of the Upper Continental Crust (UCC) except for a few elements (e.g., enrichments of Li, Mo, and clay-sized particles’ P, Zn, Cu, and Pb, and depletion of Ca and silt-sized particles’ Bi). The pellet materials are derived mainly from atmospheric dusts. Therefore, the silt pellets may provide insights into details of the large-scale fine sediment recycling between the atmospheric, glacial and alluvial systems.