Provenance study on geochemical elements of detrital K-feldspar in Quaternary gravel layer in Yichang and its geological significance

Abstract

The Yichang area located at the exit of the Three Gorges is covered with a set of thick Quaternary gravel layers, recording the evolution of the paleoenvironment and the formation of the Yangtze River. However, there has been a great dispute over the time when the Yangtze River materials in the upper reaches entered the western margin of the Jianghan Basin. K-feldspar is a common mineral in fluvial sediments, and its geochemical element compositions are significantly different in different regions, making it an ideal mineral for the fluvial provenance study. In this case, we utilized the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to analyze the elementary compositions of detrital K-feldspar grains (n=340) on the gravel layers of the Yichang area and the upper reaches of the Yangtze River. In combination of principal component analysis (PCA) with formation sedimentary ages of gravel layers, we discussed the time when they established the provenance connection. The results show that the provenance connection has been established since 1.15 Ma and a new provenance area appeared at 0.75 Ma, suggesting that the Yangtze River drainage was strongly influenced by the East and South Asian summer monsoon during the period of 1.2~0.7 Ma.

Keywords

• gravel layer in yichang
• k-feldspar
• element characteristics
• provenance tracing
• yangtze river