Sediment rock magnetic properties indicate outburst events for Gega dammed lake at the Tsangpo Gorge in the Tibetan Plateau

Abstract

A large ice-dammed lake exists at the entrance of Tsangpo gorge in the Tibetan Plateau. Many megafloods occured down the Tasangpo gorge during the last glaciation. The lacustrine sediments are important for understanding these periodic outburst floods. Through detailed rock magnetic studies of 39 lacustrine samples, we found the low frequency magnetic susceptibility (chi(If)) is high in fine sand and low in clay, but the value of susceptibility of anhysteretic remanent magnetization (chi(ARM)) and saturation isothermal remanent magnetization (SIRM) are similar. chi-T, Loop and IRM show that coarse-grained magnetite is the main magnetic minerals in fine sand. chi(ARM)/chi(If) also shows that the grain size of magnetite in fine sand is coarser than that in clay. Rock magnetic properties indicate that the fine sand of lacustrine sediment experienced no weathering damage and should be deposited near the source and then quickly buried. Thus, the rock magnetic properties of fine sand of lacustrine may indicate the outburst event, which could be a new method for detecting the event.