Magnetism parameters characteristics of drilling deposits in Jianghan Plain and indication for forming of the Yangtze River Three Gorges

The forming time of the Yangtze River Three Gorges is considered as one of keys in the research on the Yangtze River,also is one of the most disputed hotspots.In order to solve the difficult problem,the authors adopt the internationally recognized thoughts and methods of substance tracing from source to sink.The lithologic characteristics,magnetic parameters and magnetic mineral characteristics of deposits in 2 bores are analyzed,which are both sampled from the sedimentary center of the Jianghan Plain.The results are as follows:At about 110 m depth of the core,the contents of coarse materials and stable magnetic mineral both increase significantly.Meanwhile,the magnetic susceptibility of sediment,saturation isothermal remanent magnetization and magnetic susceptibility values of anhysteretic remanent magnetism increase suddenly,which all reflect that at about 110 m depth,the important adjustment has appeared in water system of the Jianghan Plain,and the sedimentary environment and material composition have changed greatly.And it may be the horizon where the Yangtze River Three Gorges formed,its forming time reflected by the paleomagnetic dating is between 1.17 and 1.12Ma B.P.