Global Hg cycle over Ediacaran-Cambrian transition and its implications for environmental and biological evolution

The Ediacaran-Cambrian (E-C) transition witnessed remarkable environmental changes, the extinction of the Ediacaran biota, and subsequent rapid diversification of Cambrian animals. However, the linkages between environmental and biological evolution are still under debate at this critical time. Here, we present new Hg abundance and Hg isotopes in sediments from South China, which are then combined with those published from the Indian craton to explore the co-evolution of environment and complex life during the E-C transition. In both areas, high Hg/TOC ratios and near-zero delta Hg-199 of the Late Ediacaran sediments suggest enhanced volcanism, whereas relatively high Hg/TOC ratios and positive delta Hg-199 shift upsection indicate volcanic-sourced atmospheric Hg(II) deposition in the earliest Cambrian. The dramatically decreasing Hg/TOC ratios and positive delta Hg-199 of early Cambrian Age 2 to 3 sediments indicate scavenging of dissolved seawater Hg(II) by organic matter particulates. Our Hg results suggest volcanism may have likely played a significant role in the extinction of Ediacaran biota and global negative carbon excursions near the E-C boundary. Furthermore, our Hg data provides new evidence of extensive OM burial in the early Cambrian Age 2 to 3 oceans, leading to a rapid increase of Earth-surface O-2 levels that coincided with appearance of more complex large-body animals. Our study provides new insights of the global Hg cycle into the co-evolution of the environment and complex life at this critical time. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the co-evolution of environment and complex life during the Ediacaran-Cambrian transition through the analysis of mercury (Hg) abundance and isotopes in sediments from South China and the Indian craton. The results suggest that volcanism played a significant role in the extinction of Ediacaran biota and global negative carbon excursions, and the burial of organic matter in the oceans during the early Cambrian led to an increase in Earth's oxygen levels and the appearance of more complex large-body animals.