Luminescence Properties Of Recent Fluvial Sediments From The Yarlung Tsangpo River And Their Implications For Provenance

The migration of sediments is an important process on the earth's surface,and is the key to understand the formation and evolution of landforms as well as solve problems such as soil erosion and disaster prevention.Sediment provenance is therefore of great significance both theoretically and practically.Actually,there are already many sediment provenance methods,including heavy mineral composition,detrital zircon U/Th age,isotopic geochemical composition,etc.However,due to the complexity of the earth system and the limitations of each method,sediment provenance still faces many challenges.Thus,it is of great need to explore new methods for mutual verification and to make the results more reliable.Luminescence is a widely used method for quaternary dating.And in the past decade,it has been exploited as a provenance tool and turned out to work well in many cases.Based on those achievements,Recent fluvial sediment samples were continuously collected along the main channel of the Yarlung Tsangpo River and the downstream branches of the Brahmaputra River.By analyzing the distribution characteristics of the OSL properties such as the residual dose of both quartz and feldspar,as well as the OSL sensitivity of quartz.the feasibility of using the luminescence property as a sediment provenance tool in the Yarlung Tsangpo-Brahmaputra river were carefully discussed.The main results are as follows:(1)Both high and low intensity of quartz luminescence signal were discovered along the main channel of the Yarlung Tsangpo river,but not in a form of an increasing line as discovered in many other rivers.Instead,it exhibited an undulating character,which coupled well with the lithological characteristics along the main channel,indicating that the sediments in most parts of the main channel of the Yarlung Tsangpo River are not from the remote source but the surrounding areas.(2)The intensity of the quartz luminescence signal of the Brahmaputra River were significantly lower than that of the Yarlung Tsangpo River,indicating that the main source area of the sediment in the Brahmaputra River is not inside the Tibetan Plateau,but more likely to be the southern foot of the Himalayas or other mountains nearby.(3)The residual dose of quartz in most samples from both the Yarlung Tsangpo River and the Brahmaputra River were less than 1 Gy,indicating that these quartz had experienced better exposure during the migration process.However,the residual dose in those gorges of the Yarlung Tsangpo River were generally high,mostly up to 5Gy.Especially in the Grand Canyon,which is the highest,reaching 29 Gy.Taking consideration of the geomorphic process of the canyon,it is believed that this is due to the rapid erosion process in the canyon,which causes a large amount of material that has not been fully exposed to be brought into the river channel.In addition,the residual doses of both quartz and feldspar in the Brahmaputra River appeared to be higher in the mainstream than in the tributaries.Combined with hydrodynamic conditions,this may be due to the fact that the main stream is more erosive than the tributary,which involves more old nearshore sediments,resulting in a higher residual dose.To sum up,those results above altogether showed that a high residual dose value indicates an adjacent source.(4)The residual dose of feldspar from the Brahmaputra river appeared to the lowest in the excitation temperature of 50? and grew up as the temperature increased,until it finally reached a “plateau” at the temperature of 140? and 170?,which was a sign that OSL signals corresponding to 140 ? and 170 ? had basically not been touched and thus may contain information of the previous deposition area and hold the potential to be used as provenance tool.