Trace element distribution and enrichment patterns of Ediacaran-early Cambrian, Ziyang selenosis area, Central China: Constraints for the origin of Selenium

All Eu/Eu* for the forty anomalous Se-enrichment samples (Se = 42-303 ppm) of the 1st Member (1.09-2.09, average = avg. = 1.40), 2nd Member (1.20-1.38, avg. = 1.29), 3rd Member (1.12-4.00, avg. = 2.38) and 4th Member (2.51-4.48, avg. = 3.56), show positive Eu anomalies and an increasing trend upward. However, Eu/Eu* of two samples are 0.90 (HSBY324, Bed 4 of 1st Member) and 0.95 (HSBY401, Bed 6 of 1st Member), which indicate that they are characterized by hydrothermal sediments, except HSBY324 and HSBY401 of 1st Member. Based on these elements' geochemical and petrographic characteristics, we conclude that these samples are of hydrothermal origin. There is also a strong positive correlation between Se and Ba (RSe-Ba = 0.738**, n = 40). In three point X-ray energy spectrometric analysis of black shale mineral anomalous Se-enrichment samples (HSBY601), the nor.C measurements of Ba (L Series) are 55.50 wt.%, 54.94 wt.% and 27.20 wt.%, respectively, with the corresponding Atom. C of 14.80, 14.50 and 5.72 at.%. Thus, the main Se source was derived from hydrothermal fluids, of anomalous Se-enrichment strata of Ediacaran-early Cambrian (ca. 635-520 Ma) of South Qinling Mountain.