A Mesoproterozoic iron formation

Research output: Contribution to journalArticle

Abstract

We describe a 1,400 million-year old (Ma) iron formation (IF) from the Xiamaling Formation of the North China Craton. We estimate this IF to have contained at least 520 gigatons of authigenic Fe, comparable in size to many IFs of the Paleoproterozoic Era (2,500–1,600 Ma). Therefore, substantial IFs formed in the time window between 1,800 and 800 Ma, where they are generally believed to have been absent. The Xiamaling IF is of exceptionally low thermal maturity, allowing the preservation of organic biomarkers and an unprecedented view of iron-cycle dynamics during IF emplacement. We identify tetramethyl aryl isoprenoid (TMAI) biomarkers linked to anoxygenic photosynthetic bacteria and thus phototrophic Fe oxidation. Although we cannot rule out other pathways of Fe oxidation, iron and organic matter likely deposited to the sediment in a ratio similar to that expected for anoxygenic photosynthesis. Fe reduction was likely a dominant and efficient pathway of organic matter mineralization, as indicated by organic matter maturation by Rock Eval pyrolysis combined with carbon isotope analyses: Indeed, Fe reduction was seemingly as efficient as oxic respiration. Overall, this Mesoproterozoic-aged IF shows many similarities to Archean-aged (>2,500 Ma) banded IFs (BIFs), but with an exceptional state of preservation, allowing an unprecedented exploration of Fe-cycle dynamics in IF deposition.

Details

Authors
  • Donald E. Canfield
  • Shuichang Zhang
  • Huajian Wang
  • Xiaomei Wang
  • Wenzhi Zhao
  • Jin Su
  • Christian J. Bjerrum
  • Emma R. Haxen
  • Emma U. Hammarlund
Organisations
External organisations
  • China National Petroleum Corporation
  • University of Southern Denmark
  • University of Copenhagen
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Geology

Keywords

  • Anoxygenic photosynthesis, Banded iron formation, Green sulfur bacteria, Mesoproterozoic, Oxygen
Original languageEnglish
Pages (from-to)E3895-E3904
JournalProceedings of the National Academy of Sciences of the United States of America
Volume115
Issue number17
Publication statusPublished - 2018 Apr 24
Publication categoryResearch
Peer-reviewedYes