Characterization of trace elements and carbon isotopes across the Ediacaran-Cambrian boundary in Anhui Province, South China: Implications for stratigraphy and paleoenvironment reconstruction

Abstract

Characteristics of redox-sensitive elements and organic carbon isotopes of a drilling section covering the Ediacaran-Cambrian (E-C) boundary at Anhui Province, South China were studied. Total organic carbon (TOC), organic carbon isotope values of organic compounds, abundances of Mo, V, U, and Ni, and ratios of V/(V+Ni) and Th/U co-vary across the section, suggesting that the redox condition is the main factor controlling carbon isotope values of organic matter, and sequestration of trace elements. The E-C boundary is characterized by the lowest organic carbon isotope and the highest ratios of Mo/TOC, V/TOC, and U/TOC in the section, which are correlated with reported carbon isotope excursions in other regions. This is the first time that signatures of Mo, V, and U in the Hetang Formation at the Lower Yangtze Platform are used for stratigraphic correlations. The results highlight abnormally high ratios of Mo/TOC, V/TOC, and U/TOC near the E-C boundary. Petrological and geochemical characteristics in this section suggests that intense upwelling activities during the E-C transition may be the main contributor to 13C-depleted CO2 and enrichment of trace metals. The co-existing pervasive transgression led to ocean anoxia and facilitated the preservation of 13C-depleted organic matter and trace metal sequestration. Furthermore, oxidation of the bottom ocean water may have completed during the early Cambrian. A combination of these factors may be among the reasons for significant evolutionary changes during the E-C transition.