Microbial Fossils in the 2.63 Ga Jeerinah Formation, Western Australia—Evidence of Microbial Oxidation

ABSTRACT

A diamond drill core from the upper part of the Jeerinah Formation (∼2.63 Ga), underlying the Hamersley Group, deposited at a time when the oxygen concentrations in the marine environment were extremely low, was examined for microbial fossils. The paper presents organo-mineral structures in the form of twisted stalks produced by bacteria being present in the laminated black carbonaceous shale sediments. These twisted stalks are organo-mineral structures produced by microaerophilic Fe(II)-oxidizing-type bacteria such as Gallionella and/or Mariprofundus that are active at very low-oxygen concentrations, thus providing evidence for oxygen being present in the marine environment at 2.63 Ga.

KEYWORDS:

• Banded iron formations
• Gallionella
• Mariprofundus
• microbial fossil
• oxygen evolution

Acknowledgments

The authors thank Hamersley Exploration Pty Ltd for providing core material and personal transportation of Hallberg between Perth and Tom Price. Hallberg thanks senior geologist W. Burns for excellent guiding at the mine site for 2 days.

Funding

Funding was provided by the Swedish Natural Science Research foundation for Hallberg's trip to Australia.