Acta Geographica Sinica ›› 2015, Vol. 70 ›› Issue (1): 63-72.doi: 10.11821/dlxb201501005

• Orginal Article • Previous Articles     Next Articles

Eolian loess- palaeosol sequence and OSL age of the first terraces within the Yunxian Basin along the upper Hanjiang River

Jiangli PANG(), Chunchang HUANG, Yali ZHOU, Xiaochun ZHA, Yuzhu ZHANG, Leibin WANG   

  1. College of Tourism and Environmental Sciences, Shaanxi Normal University, Xi'an 710062, China
  • Received:2014-10-16 Revised:2014-11-15 Online:2015-01-20 Published:2015-06-17
  • Supported by:
    National Natural Science Foundation of China, No.41271108, No.41030637, No.41371029;Fundamental Research Funds for Central Universities, No.GK201301003

Abstract:

The first river terrace within the Yunxian Basin along the upper reaches of Hanjiang River was investigated in the field work. The sediment profiles were sampled systematically. The sedimentological characteristics, and physical and chemical properties were analyzed in laboratory. The samples were dated using OSL method. The results show that, the bottom age of the thick loess L1 is 25 ka BP, and the age range of the eolian loess-alluvial sand inter-beds (T1-al2) is between 55-25 ka BP. The age distribution suggests that deposition process of the loess sequence in Hanjiang River valley is essentially continuous. The first river terrace of the Hanjiang River has experienced two development stages, including the tectonic uplift and river incision (55-25 ka BP), and then the stabilized eolian loess deposition (25-0 ka BP). Around 55 ka BP, the river incision started because of the intensified tectonic uplifting. The eolian loess accumulation on the uplifted flood plain was frequently interrupted due to the overbank flooding. This process continued around 25 ka BP and the inter-beds of eolian loess and alluvial sand (T1-al2) were therefore formed. To about 25 ka BP, the first river terrace had formed and eolian loess accumulated continuously on the terrace land. At the same time, with the river incision, the last glaciation entered the maximum stage and the thickeolian loess covered the terrace because of the increased dust storms and dustfalls. Since the formation of the terrace about 25 ka BP, the eolian loess experienced varying degrees of weathering and pedogenesis in different periods because of monsoonal climate change. The stratigraphic paleosol-loess sequence on the first terrace from the bottom to the top is listed as fluvial gravel (T1-al2) → eolian loess and alluvial sand inter-beds (T1-al2) → Malan loess (L1) → transitional loess (Lt) →paleosol (S0) → recent loess (L0) → modern soil (MS). This stratigraphic sequence has recorded a monsoonal climate change model since 25 ka BP, including the gradually intensified southeast monsoon during the late glacial and early Holocene periods, the strongest monsoon in the mid-Holocene, and the monsoon recession and the climate drying during the late Holocene.

Key words: Hanjing River, river terrace, OSL age, eolian loess, climatic change