Mercury enrichments in the black shale unit of the Ediacaran Doushantuo Formation are, likely the result of volcanic input or anoxia-driven mercury deposition. If the Hg enrichments are volcanic in origin, or are due to synchronous regional anoxia, then the patterns of Hg enrichment are consistent with the conventional correlation of these units, with the tripartite units equivalent to Member IV black shales. Additionally comparing redox proxy data from the intervals of Hg enrichment could indicate if the enrichments are due to comparable changes in redox conditions, or increased Hg input under differing redox conditions, consistent with volcanic input.
Los enriquecimientos de mercurio en la unidad de esquisto negro de la Formación ediacárica de Doushantuo son probablemente el resultado de la influencia volcánica o del depósito de mercurio mediante anoxia. Si los enriquecimientos de Hg son de origen volcánico, o se deben a una anoxia regional contemporánea, entonces los patrones de enriquecimiento de Hg son consistentes con la correlación convencional de estas unidades, con las unidades tripartitas equivalentes a la pizarra negra del Miembro IV. Además, la comparación de los datos redox de los intervalos de enriquecimiento en Hg podría indicar si los enriquecimientos se deben a cambios comparables en las condiciones redox, o a un aumento de la entrada de Hg bajo diferentes condiciones redox, consistente con la influencia volcánica.
The Ediacaran Period is a critical time interval in the history of life, when environmental changes and evolutionary events set the stage for the Cambrian explosion of animal diversity (e.g. Marshall,
Understanding these histories requires stratigraphic correlation between sections of the Doushantuo Formation, especially correlations among black shale units (Member IV, Miaohe Member, and Lower Black Shale). Conventionally, the Member IV is correlated to the tripartite Lower Black Shale, Upper Dolostone, and Miaohe Member; however, some δCcarb data suggests that only the Lower Black Shale correlates to the Member IV, thus the Miaohe Member correlates to the Shibantan Member and the Upper Dolostone correlates to the Hamajing Member of the overlying Dengying Formation (An
Samples were collected from six sections of the Doushantuo Formation around the Huangling Anticline of south China (
Mercury concentrations from sections of the Doushantuo Formation around the Huangling Anticline. A. Qinglinkuo Section. There is a large positive mercury concentration enrichment in the LBS unit and a moderate enrichment in the MM unit. Stratigraphic column modified from An
To improve sectional comparisons, mercury concentration is normalized with Total Organic Carbon content (TOC) to account for differential sedimentation rates between sections over time. TOC data are available only for the Jiulongwan section (McFadden
Mercury concentration data of the Doushantuo Formation from the Jiulongwan Section. Left profile shows concentrations, and right profile shows mercury concentrations normalized by total organic carbon content (TOC). The data support intervals of heightened mercury concentration in the upper and lower parts of Member IV. The normalized data also show considerable variance and large mercury spikes. These are likely noise due to very low organic carbon content (< 0.1% TOC), while the Member IV signals are all based on greater organic carbon content (between 0.2% and 8% TOC). TOC data from McFadden
There are clear mercury enrichments in the black shale units, likely the result of volcanic input or anoxia-driven mercury deposition. If the Hg enrichments are volcanic in origin, or are due to synchronous regional anoxia, then the patterns of Hg enrichment are consistent with the conventional correlation of these units, with the tripartite units equivalent to Member IV black shales. Furthermore, a volcanic origin would offer targets for radiometric dating. The source of the Hg enrichment can be explored via comparison of mass-independent and mass dependent Hg. isotopic fractionation. Additionally comparing redox proxy data from the intervals of Hg enrichment could indicate if the enrichments are due to comparable changes in redox conditions, or increased Hg input under differing redox conditions, consistent with volcanic input.