Heavy mineral characteristics of gravel layers in the Zhoulao Town borehole

Abstract：A borehole was drilled at Zhoulao Town in Jianghan plain, and then ten gravel layers in core sediments were analyzed in order to study heavy mineral components and distribution characteristics of the fillings. The results show that the ten gravel layers can be divided into three mineral stages from bottom to top. A comparative study of the stable and unstable heavy minerals of the three stages has revealed that the variation characteristics are as follows: sediments of stage 1 and 2 are composed mainly of distal materials with a small amount of proximal materials, whereas the major sediments of stage 3 are distal materials mixed with a certain amount of proximal materials. Based on core lithology and gravel contents as well as Quaternary lithofacies features of Jianghan plain, the authors hold that at the depth of 112.30～109.05 m in the borehole (1.17-1.12 Ma.B.P., namely stage 3), the sedimentary environment changed remarkably, and the water system of the Jianghan plain underwent considerable variation, which finally led to the formation of the Three Gorges on the Yangtze River.