Enrichment of mercury in the Lower Cambrian sedimentary successions by submarine hydrothermal venting

Abstract

• Widespread sedimentary Hg enrichments in the Early Cambrian can be attributed to periodic hydrothermal ventilation. • Prevailing hydrothermal ventilation was an important source of Hg in sediments in the Early Cambrian. • The accumulation of Hg in sediments may be more effective in euxinic environments. Although extremely high Hg contents are known in the Lower Cambrian sedimentary successions, the extent and spatial-temporal distribution of sedimentary Hg anomalies in these successions remain unclear. Here, we report concentrations of Hg, total organic carbon (TOC), total sulfur (TS), and major and rare earth elements of the Lower Cambrian (∼525 Ma) sedimentary rocks at the Dongxihe section in the interior of the Yangtze Platform, South China. We investigated the sedimentary Hg enrichment mechanism and the spatial-temporal fluctuations of Hg in the Lower Cambrian and compiled published Hg (Hg/TOC) data from the Upper Neoproterozoic to the Lower Cambrian to trace the potential Hg sources. Our study verified that hydrothermal vents provide an excess Hg source for the sedimentary Hg enrichment in the Dongxihe section, which is supported by the positive Eu anomaly and major element. The major elements show more Fe and Mn enrichment in the upper part than the lower part, indicating more hydrothermal contribution in the upper part. Additionally, the records of the spatial-temporal distribution of Hg show that most of the sections (including shelf, slope, and basin) in South China show strong sedimentary Hg enrichment, which can be attributed to widespread hydrothermal venting. By reconstructing fluctuations of Hg during the Late Neoproterozoic to the Early Cambrian, we proposed that in the context of the Gondwana continent assembly, the prevalent hydrothermal ventilation event during the Early Cambrian not only induced the abnormal enrichment of sedimentary Hg but also played a crucial role in shaping the marine environment and ecosystem during this period.