Source of selenium in Handan geochemical anomaly belt: Evidences from petrology and geochemistry of Upper Paleozoic in western Handan, China

Handan lies in a geochemical anomaly belt characterized by enrichment of selenium (Se) in rock, soil, and water, contrasted with deficiency of Se in the North China Plain. In this study, 27 environmental soil samples and 96 rock samples in the Upper Paleozoic were analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) for major and trace element concentrations to determine the source of Se in the environment. Se concentrations in soil vary from 0.054 μg/g to 2.869 μg/g, with an average of 0.598 μg/g. Ignoring the anthropogenic contamination, Se concentrations in soils elevate with the decrease of distance from outcrops in Mountain Zishan (Mt. Zishan). There is a strong positive correlation between Se and Al2O3 (r = 0.679, P Ga > Li > Bi > Th > Sc > In > U > Cd > Y > Rb > Ba > Cr > V > Be > Cs > Ni > Zn > Tl > Sr > Co > Mo > Cu. Se enrichment appears in two types of rocks, which are gray clay rocks and black mudstones and shales (including coal and gangue). Stratigraphically, Se is more highly enriched in TY Fm. and SX Fm., with average enrichment factor (EF) values of 14.64 and 5.59, respectively. Chemical index of alteration (CIA) and several environmentally sensitive elements, such as Th, U, Sr, Ba, V, Cr, and Ce, were employed for sedimentary environment analysis. The results revealed that Se-enriched rocks were deposited mainly in a weak, reducing freshwater environment, and their sediments were subject to an intermediate chemical weathering process. The discrimination diagrams of SiO2-TiO2, F1-F2, ∑REE-La/Yb, and La/Sc-Co/Th indicate that the terrestrial clastic s