PROGRESS IN GEOGRAPHY ›› 2017, Vol. 36 ›› Issue (4): 454-465.doi: 10.18306/dlkxjz.2017.04.007

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Grain-size and sedimentary records of the XYC Core in the downstream of the Cao’e River

Lidong ZHU(), Jun WANG, Haojie PEI, Wei YE, Fengquan LI, Dongpo MO, Haiyi LIN   

  1. College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua 321004, Zhejiang, China
  • Received:2016-09-01 Online:2017-04-20 Published:2017-04-20
  • Supported by:
    National Natural Science Foundation of China, No.41371206, No.41572345

Abstract:

Based on the analysis of grain-size constitution and distribution curves of the XYC core in the downstream of the Cao'e River—the central section of the Ningshao plain, we arrived at the following conclusions: (1) According to the grain-size constitution, the sediments of the XYC Core can be divided into four lithologies: silty sand, sandy silt, silt, and clayey silt. They distribute along the core alternately. The core is divided into 9 layers and they compose multiple grain-size combinations. The 9 layers are marked as layer 1 to layer 9 from the bottom to the top. Among them, layer 1 and layer 4 are silty sand, and the percentage of clay is 10%~15%, which is poorly sorted and the dynamics is complicated. Layer 3 and layer 5 are sandy silt, the percentage of silt is no more than 70%, and clay is more than 20%. The percentage of clay is low. Layer 2, layer 7, and layer 9 are silt, the percentage of silt is more than 70%, and clay and sand are less than 20%. Layer 6 and layer 8 are clayey silt, the percentage of silt is more than 70%, and clay is more than 20%. The percentage of sand is very low. (2) According to the C-M graph of the max and the mean values and the analysis of its variation, there were four types of deposits from the bottom to the top: fluvial, tidal flat, shallow marine, and lakes and marshes. For layer 1 and layer 2, the hydrology was high energy and unstable, which indicates a fluvial environment; for layer 3 to layer 7, the max hydrology weakened, but the mean hydrology was strong and the range was still wide, and the hydrology was similar to the SYTT tidal flat samples. It referred to a tidal flat environment; for layer 8 and layer 9, the hydrology was weak and stable, which indicates still water environment. Based on the grain-size and biology information, it can be concluded that the under part of layer 8 belonged to shallow marine environment, but the upper part and layer 9 belonged to lakes and marshes environment. (3) Vertical variation of grain-size indicates that clay increased from the bottom to the top with fluctuation, while sand declined. The average grain diameter is decreasing and the sorting coefficient is higher. The sediments change from the bottom to the top reveals that the XYC Core and its adjacent area experienced sea level rise, and then water level decreased during 9690~5131 cal.a BP. The results of the study are helpful for identifying the paleoenvironmental evolution characteristics of the Qiantang River Basin.

Key words: downstream of the Cao'e River, grain-size, sediment, environmental change of deposit