Origin and enrichment of Selenium in Permian strata in the northern part of Jianshi, Hubei

During 1∶50 000 geological mapping in the northern part of Jianshi, Hubei, the authors investigated three Permian selenium anomaly horizons—the Gufeng, Wujiaping and Dalong Formations—in the area. Basic pyroclastic rocks were found in the selenium anomaly horizons or their underlying horizons. The selenium content is positively proportional to basic pyroclastic rocks in the stratigraphic sequence and in plan distribution. The consistency of the geologic ages suggests that the selenium source is related to eruption or weathering of the Emeishan basalt in Southwest China. The selenium content variation displays a positive correlation with the sea level fluctuation curve, with the selenium content reaching a maximum at the highest marine flooding surface. The large hosting space and the environment with relative flow water body energy as well as the use of organic carbon to absorb a significant amount of selenium result in enrichment of selenium.