PROGRESS IN GEOGRAPHY ›› 2012, Vol. 31 ›› Issue (11): 1467-1474.doi: 10.11820/dlkxjz.2012.11.007

• Original Articles • Previous Articles     Next Articles

Characteristics of Palaeoflood Slackwater Deposits of Yunxian County in the Upper Reaches of the Hanjiang River

QIAO Jing, PANG Jiangli, HUANG Chunchang, ZHA Xiaochun, ZHAO Yanlei, ZHANG Yuzhu   

  1. College of Tourism and Environmental Sciences, Shaanxi Normal University, Xi’an 710062, China
  • Received:2012-03-01 Revised:2012-07-01 Online:2012-11-25 Published:2012-11-25

Abstract: Palaeoflood slack water deposits (SWD) are very useful for hydrological reconstruction. Search for SWD has become a key step in the study of palaeoflood hydrology. Three types of sediments (palaeoflood SWD, paleosol and loess) are surveyed over the first level river terraces of the upper Hanjiang valley. Comprehensive analyses of macroscopic characteristics, grain-size distribution, magnetic susceptibility, loss-on-ignition, micromorphology, and major-elementcomposition are conducted in the laboratory. Results are shown as follows. (1) The color of palaeoflood slackwater deposits in the upper Hanjiang valley is gray-yellow (2.5 YR 7/2), with abrupt vertical changes and clear boundaries in the adjacent stratigraphies. (2) The palaeoflood SWD has coarse texture with silty fine sand, and is better sorted than other types of sediments, indicating that this type of sediment was formed by the suspended sediment load of floodwater. However, compared to palaeoflood SWD in the Weihe river valley, the latter is even better sorted because the majority of it is silty fine sand with even smaller grain size. (3) The magnetic susceptibility of the palaeoflood SWD is slightly higher than that of loess, but significantly lower than that of luvisols. (4) Loss-on-ignition of palaeoflood SWD is lower than that of loess and paleosol, which suggests that the palaeoflood SWD was fresh sediment without being affected by weathering and pedogenesis after deposition. (5) In micromorphology, the surface of the palaeoflood SWD is distributed with V-shaped pits, typically caused by physical collision and friction in running water. (6) The palaeoflood SWD is also different from paleosol and loess in major-element compositions and UCC (upper continental crust)-normalized patterns. These results are of great importance to the identification of the palaeoflood slackwater deposits in the upper Hanjiang valley and the reconstruction of the palaeoflood hydrological parameters.

Key words: Holocene, palaeoflood, slackwater deposits, the upper Hanjiang River