A diverse Ediacara assemblage survived under low-oxygen conditions

Area of Science:

• Paleontology
• Geochemistry
• Marine Biology

Background:

• The Ediacaran biota were early soft-bodied organisms with uncertain evolutionary relationships and metabolisms.
• Hypotheses range from metazoan affinity with aerobic respiration to a separate group relying on chemoautotrophy.

Purpose of the Study:

• To investigate the redox conditions experienced by Ediacaran organisms.
• To test the hypothesis of aerobic metabolism versus anaerobic or chemoautotrophic lifestyles.
• To understand the environmental context of Ediacaran fossil preservation.

Main Methods:

• Analysis of local and global redox datasets from Siberian carbonates containing in situ Ediacaran fossils.
• Measurement of cerium anomalies to assess local anoxia.
• Analysis of uranium isotope (δ238U) values to determine global marine euxinia.

Main Results:

• Cerium anomalies consistently greater than 1 indicate pervasive local anoxia in fossil-preserving environments.
• δ238U values suggest widespread marine euxinia during the terminal Ediacaran.
• Ediacaran biota preserved in situ appear tolerant of anoxic conditions.

Conclusions:

• Some Ediacaran organisms likely possessed the capacity for facultative anaerobic lifestyles.
• The dynamic redox landscape of the Ediacaran-Cambrian transition influenced these early life forms.
• Fossil preservation conditions were anoxic, potentially influencing interpretations of Ediacaran ecology.