Trace element characteristics and sedimentary environment of lacustrine carbonate rocks in the Huanghua Depression, Bohai Bay Basin

Carbonate rocks dominate in the lower part of the first member of Shahejie Formation in the Huanghua Depression, Bohai Bay Basin. The geochemical characteristics of trace elements in Kongdian-Yangsanmu, Qijiawu and Qinan show that the content and distribution of trace elements varied in different pays, but those of Sr, Ba, V, Mn, Th, U were similar, and the contents of Ni, Pb, Zn and others tended to decrease from Qijiawu to Yangsanmu, indicating environmental changes during the diagenesis process. The B content varied (7.5-92.8)×10-6 with an average of 42.8×10-6 in Qijiawu, and varied (7.2-97.4)×10-6 with an average of 45.21×10-6 in Kongdian-Yangsanmu, indicating an alternating process of saline to fresh water environments. The Ti content varied (946-3 496)×10-6 and averaged 2 319×10-6 in the lower part of the first member of Shahejie Formation from Kongdian to Yangsanmu, showing nearby provenance characteristics. The V/(V+Ni) ratio indicated strong reducingenvironment in the study area, and the low Th/U ratio showed a higher salinity of lake water or the influence of seawater intrusion.