Abstract：Division of sedimentary cycles from the Yellow River sediments under Kaifeng City is the groundwork to illustrate the relationship between the decline of Kaifeng City and the Yellow River floods in history. However, traditional method dividing sedimentary cycle with granularity cannot be used to the sediments under the city because the normal granulometric sequence of the sediments were disturbed significantly by human activities, such as city reconstructions, looking for treasures buried in sediments, etc. after flood events. Therefore we must discover other proxy indicators instead of granularity to divide flood sedimentary cycles in urban areas. Three sedimentary cores (ZKsz, ZKyz and ZKjm) of 25 m were drilled in April, 2012. ZKsz and ZKyz are in the central urban area of Kaifeng City, and ZKjm is in the western suburbs of the city that is the reference core on the study. The core sections were split fresh in the field at most 10 cm interval and a total of 657 samples were acquired and stored in sample boxes. Concentrations of Pb, Cd, Cu, Zn, Ni, V, Cr and Co in samples were measured with the instrument of Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) , Mn, Al, Fe, and P with Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) , and Hg and As with Atomic fluorescence spectrometer (AFS) . The integrated enrichment factor (IEF) of elements from human and biology was defined in this paper. With IEF as a proxy indicator, sedimentary cycles were divided based on the wavelet analysis with the help of MATLAB 7.0 software. The results show that the elements of Ni, Cr, Fe, Mn, Co, V and Al in cores are primarily of natural sources, while Cd, Pb, Cu, Zn, Hg, As and P are anthropogenic-biogenic elements from human activities and biology. Most boundaries of the sedimentary cycles divided by granularity (sand-clay ratio) in ZKsz and ZKyz are consistent with IEF in ZKjm less disturbed by human activities, indicating IEF can be used as a proxy indicator dividing sedimentary cycles. There are eight element cycles in ZKsz upper stratum from 0 to 12 m, and six element cycles in ZKyz from 0 to 9 m, which are more than their granularity cycles, indicating that IEF can avoid the human disturbance to normal granulometric sequence and element cycles can inverse the Yellow River flood frequency accurately. The ancient Daliang City in the Warring States Period, Dongjing City in the Song Dynasty, Kaifeng City in the late Ming Dynasty and Kaifeng City in the late Qing Dynasty were buried under the ground of 10 to 12 m, 9 m, 4 m and 1 m respectively in the area within the city wall of Kaifeng City nowadays.
Keyword：Yellow River flood sediments; anthropogenic-biogenic elements; sedimentary cycle; proxy indicator; Kaifeng;
【source】Geographical Research2017年06期
