REE composition and its geological implications of the Hetang Formation mudstones in the East Jiangxi and west Zhejiang, China

The provenance, tectonic setting and sedimentary environment of the Lower Cambrian black shale named Hetang Formation in the east Jiangxi and west Zhejiang of the Lower Yangtze platform are studied in this paper. Characteristics of rare earth elements (REEs) are revealed from 22 outcrop samples and 15 core samples of the Well ZJD-1. It suggests that the total amount of rare earth elements in the Hetang Formation of the study area vary substantially from 16.83 to 321.22×10⁻⁶, with a lowest mean value around 103.11×10⁻⁶. Light rare-earth elements are obviously enriched and differentiated, while the heavy rare-earth elements deficit and poorly differentiated. Commonly observed are negative Ce and positive Eu anomalies. Combined with previous researches, we reached the followings as conclusions. (1) The Hetang Formation was deposited in a rift basin with anoxic water along a passive continental margin tectonically. The provenance of the sediments was jointly controlled by the terrestrial source and the outputs from seawater and hydrothermal fluid. The region of Hengfeng and Shangrao is little affected by terrigenous debris, but substantially influenced by the materials from hydrothermal fluid and seawater, and the region of Changshan and Jiangshan is just the opposite. (2) The Hetang Formation is obviously affected by hydrothermal activities, and the low temperature hydrothermal activity is favorable for the deposition and enrichment of organic matters. The hydrothermal activity was centered at Shangrao, with decreasing influence from west to east.