Constraints of paleoenvironment on selenium enrichment of the Ediacaran-Cambrian transition period Lujiaping Group in the North Daba Mountains, China

Abstract

The Lujiaping Group (LG), a diachronous unit spanning the Ediacaran-Cambrian transition period in the North Daba Mountains, China, exhibits notable selenium (Se) enrichment. However, the distribution patterns and enrichment mechanisms remain poorly understood. In this study, we analyzed the elemental content and lithology of 61 rock samples from the LG named section in Ziyang County. The Se concentrations ranged from 0 ∼ 147.86 μg/g, with an average of 16.31 μg/g. The LG was subdivided into 5 Formations (Doushantuo Formation (DST), Dengying Formation (DY), Huoshiwan Formation (HSW), Baihe Formation (BH), Shanpingshang Formation (SPS)) from bottom to top, all showing Se enrichment with average enrichment factor (EF=content/upper continental crust (UCC))>2. The BH of the Terreneuvian of the Cambrian showed the highest Se enrichment (mean EF=663.56), while the upper part of the SPS of the Series 2 of the Cambrian showed the lowest Se enrichment (mean EF=3.45). Geochemical and petrographic characteristics suggest that hydrothermal influence was most pronounced in the DST to the lower part of the HSW, while the upper part of the HSW to the SPS received more input from terrestrial sources, and the upper part of the HSW to the lower part of the SPS received more from organism sources. Additionally, paleoenvironmental and paleoclimatic factors such as alternating anoxic-euxinic and suboxic conditions, high primary productivity, intermittent upwelling, and a warm, moist climate may have further promoted Se enrichment.