Abstract: Several thick gravel layers are widely distributed in the middle reaches of the Yangtze River, providing useful clues for tracking the evolution of the Yangtze River. Previous studies mainly focused on the chronologies and sedimentary characteristics of gravel layers in local sites, while comparison of gravel layers among different regions has not been extensively investigated. In this study, eleven profiles of gravel layers in Yichang and Wuhan were explored, the morphology and lithology of 1616 gravels were analyzed. Furthermore, geochemical composition of silty sediments intermixed in gravel layers were measured in order to explore the provenance of the sediments, in combination with regional geological conditions. The results show that the dominant inclinations of gravels in the gravel layers of Yichang and Wuhan are different. Gravels in the Yichang gravel layers mainly consist of granite, sandstone, conglomerate and some siliceous rocks. Gravels in Wuhan are dominated by quartzite, with a small amount of flint. Silty sediments in the gravel layers of Yichang are relatively enriched in Ca and Sr, while those in Wuhan are relatively enriched in Fe and Al. Comparison of gravels and silty sediments in the two regions shows that the provenances of gravel layers in the two regions are different. Detritus from the upper reaches of the Yangtze River are important sources of the gravel layers in Yichang, while the gravel layers in Wuhan are sourced from the Dabie Mountains. The results of this study provide new evidence for improving our understanding of the provenances of gravel layers in the middle reaches of the Yangtze River.

Key words: gravel lithology, gravel inclination, geochemical analysis, The Three Gorges Region, the Dabie Mountains