Response of modern fluvial sediments to regional tectonic activity along the upper Min River, eastern Tibet

[摘要] The deposition of fluvial sediments in tectonically active areas is mainlycontrolled by tectonics, climate, and associated Earth surface processes;consequently, fluvial sediments can provide a valuable record of changes inregional climate and tectonic activity. In this study, we conducted adetailed analysis of the grain-size distribution in modern fluvial sedimentsfrom the upper Min River, eastern Tibet. These data, combined withinformation on regional climate, vegetation, hydrology, geomorphology,lithology, and fault slip rate, indicate that modern regional tectonicactivity along upper Min River can be divided into three segments.Specifically, fluvial sediments in the Minjiangyuan–Diexi segment aredominated by silts (  63  µ m, 70.2 %), agreeing withlow runoff, low rainfall, and high vegetation cover and revealing a windblownorigin influenced by the arid and windy climate. These observations areconsistent with the low hillslope angle and low relief, all indicating weakactivity along the Minjiang Fault. The coarse-grained fraction ( >  250  µ m) of fluvial sediments in the Diexi–Wenchuan and Wenchuan–Dujiangyan segments increases stepwise downstream, although runoff andrainfall do not change significantly. These patterns correlate well withincreases in both regional relief and hillslope angles. Together, theseobservations imply that regional tectonic activity along the Maoxian–WenchuanFault becomes more pervasive downstream along the Min River. The occurrenceof well-sorted and well-rounded pebbles of fluvial sediments downstreamof Dujiangyan must be related to the long-time scouring and sorting byrivers. This study marks the first development of a new research approachthat can characterize regional tectonic activity by analysis of grain-sizedistribution of fluvial sediments collected from tectonically activeregions.

[学科分类] 土壤学