Abstract:

A large quantity of gravel depositions is located in the middle reaches of the Yangtze River, especially at Yichang and Yangluo near Wuhan City. In order to investigate the magnetic characteristics and constrain the source of these gravel depositions, the magnetic characteristics of these sediments were studied. The results are as follows: 1)The content of ferromagnetic minerals in these profiles are different, with the Yunchi profile having highest concentrations, followed by Shanxiyao, Honghuatao, Baiyangdu and Yangluo profiles. 2)The results of SIRM/χ and F₃₀₀ show that magnetic properties in the gravel depositions in the midstream of Yangtze River is dominated by ferromagnetic minerals. The Yangluo profile has the highest antiferromagnetic mineral proportions. 3)The values of χ_ARM/χ，χ_ARM/SIRM and χ_fd suggest that the magnetic minerals grains in Baiyangdu, Honghuatao and Shanxiyao profiles are coarser, but the magnetic minerals in Yunchi and Lijiayuan profiles are characterized by relatively finer grain. The magnetic particles in Yangluo profile near Wuhan City are dominated by single domain and superparamagnetic particles. 4)The magnetic characteristics of Shanxiyao, Yunchi, Honghuatao and Baiyangdu profiles are similar to these of present sediment of the Yangtze River, suggesting that these sediments were fed by the Yangtze River. However, the magnetic characteristics of Yangluo is similar to the modern sediments of the rivers around the Jianghan basin, which means that the sediment in Yangluo comprise a mixture of detritus derived from the Yangtze, Han River and some small rivers on the periphery of the Jianghan basin.

Key words: the middle reaches of Yangtze River, high position gravel, magnetic characteristics, provenance