摘要
Based on the principle that the present is the key to the past , detailed analyses, such as AMS 14C dating, grain size, component and morphology of heavy minerals, micro-morphology of zircon, Rb/Sr, magnetic susceptibility and total organic carbon (TOC), were conducted to identify paleoflood sediments archived in Zhongba Site. The results indicate that the plaeoflood sediments bear great similarities with modern flood sediments in the following aspects: (1) probability cumulative curves mainly show a pattern of 3―4 segments; (2) grain-size distribution of suspended matter ranges between 3 and 10Ф; (3) the sediments are well-sorted, most of which are suspended matter (>50%); (4) the same species, quantity and morphology of heavy minerals; (5) scanning electronic microscope images show that shapes of zircon are mainly oval and nearly spheral, rounded due to long-distance transport; (6) higher Rb/Sr values (0.55―0.66)than those of sediments from cultural layers (0.03―0.26); (7) magnetic susceptibility values (133.73―433.05 10-6m3/kg) are lower than those of sediments from cultural layers (959.25―2442.44 10?6 m3/kg); (8) TOC (0.14%―0.33%) are lower than those of sediments from cultural lay-ers (1.13%―2.95%). Our results demonstrate that, except for the 1981 flood, there are at least six paleoflood events that occurred during the Qing Dynasty, the middle of Song Dy-nasty, the early Warring States (400BC―350BC), the West Zhou Dynasty (920BC―900BC), the Xia Dynasty (2070BC―1600BC), and the late Neolithic Age (3000BC―2300BC), respectively .
Based on the principle that the present is the key to the past, detailed analyses, such as AMS ^14C dating, grain size, component and morphology of heavy minerals, micro-morphology of zircon, Rb/Sr, magnetic susceptibility and total organic carbon （TOC）, were conducted to identify paleoflood sediments archived in Zhongba Site. The results indicate that the plaeoflood sediments bear great similarities with modern flood sediments in the following aspects： （1） probability cumulative curves mainly show a pattern of 3-4 segments; （2） grain-size distribution of suspended matter ranges between 3 and 10（I）; （3） the sediments are well-sorted, most of which are suspended matter （〉50%）; （4） the same species, quantity and morphology of heavy minerals; （5） scanning electronic microscope images show that shapes of zircon are mainly oval and nearly spheral, rounded due to long-distance transport; （6） higher Rb/Sr values （0.55-0.66）than those of sediments from cultural layers （0.03-0.26）; （7） magnetic susceptibility values （133.73-433.05 10^-6m^3/kg） are lower than those of sediments from cultural layers （959.25-2442.44 10^-6 m^3/kg）; （8） TOC （0.14%- 0.33%） are lower than those of sediments from cultural layers （1.13%-2.95%）. Our results demonstrate that, except for the 1981 flood, there are at least six paleoflood events that occurred during the Qing Dynasty, the middle of Song Dynasty, the early Warring States （400BC-350BC）, the West Zhou Dynasty （920BC-900BC）, the Xia Dynasty （2070BC-1600BC）, and the late Neolithic Age （3000BC-2300BC）, respectively.
基金
supported by the Key Project of the National Natural Science Foun-dation of China(Grant No.90411015)
the National Natural Science Foundation of China(Grant No.40271103)
Open Foundation of the State Key Laboratory of Loess and Quaternary Geology from the Insti-tute of Earth Environment,CAS(Grant No.SKLLQG0503)
Physical Geography of“985”Item and Foundation of Modern Analyses Center of Nanjing University.
关键词
中国
扬子江
蓄水池
防洪设施
沉积物
地球化学
Zhongba Site, identification of paleoflood deposits, shapeof zircon, Rb/Sr, magnetic susceptibility, geochemistry indexes
