Nature and genesis of till silt pellets from the shuanghu area, central Tibetan Plateau, China

摘要

Distinctive silt pellets were identified in a diamicton profile, 1 km north of the town of Shuanghu on the central Tibetan Plateau. The characteristics (mineral composition, texture, structure, fabric, and striations) of the diamicton indicate that it was formed under ice as subglacial melt-out or lodgment till. Comparing the shape, size, grain composition, and preservation of the pellets in this area with published pellet studies, we conclude that silt pellets from the Shuanghu area are formed by in situ melting out of dead ice (containing pellets) within subglacial till. We estimate that the till was deposited no later than Marine Isotope Stage (MIS) 8, based on nearby numerical ages for post-glacial fluvial terraces and the overall Quaternary glaciation history of the Tibetan Plateau. This is the first time that silt pellets have been identified in glacial deposits on the Tibetan Plateau. Detailed examination of the characteristics and formation of silt pellets has the potential to provide new insight into the basal condition of paleo-glaciers on the Tibetan Plateau.