The Significance of Iron-Formation in the Precambrian Stratigraphic Record

  1. Wladyslaw Altermann2 and
  2. Patricia L. Corcoran3
  1. A. F. Trendall

Published Online: 12 MAR 2009

DOI: 10.1002/9781444304312.ch3

Precambrian Sedimentary Environments: A Modern Approach to Ancient Depositional Systems

Precambrian Sedimentary Environments: A Modern Approach to Ancient Depositional Systems

How to Cite

Trendall, A. F. (2002) The Significance of Iron-Formation in the Precambrian Stratigraphic Record, in Precambrian Sedimentary Environments: A Modern Approach to Ancient Depositional Systems (eds W. Altermann and P. L. Corcoran), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304312.ch3

Editor Information

  1. 2

    Institut für Allgemeine und Angewandte Geologie, Ludwig-Maximilians-Universität München, Luisenstrasse 37, D-80333 Munich, Germany

  2. 3

    Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H 3J5, Canada

Author Information

  1. School of Physical Sciences, Curtin University of Technology, GPO Box 1987, Perth 6000, Western Australia

Publication History

  1. Published Online: 12 MAR 2009
  2. Published Print: 18 FEB 2002

ISBN Information

Print ISBN: 9780632064151

Online ISBN: 9781444304312



  • significance of iron-formation in precambrian stratigraphic record;
  • iron-formation and where it occurs;
  • Hamersley group BIFs as examples;
  • iron-formation in precambrian record;
  • scales of banding in Dales Gorge member;
  • lateral stratigraphic continuity;
  • microbands as varves - key to depositional model;
  • early precambrian BIF;
  • neoproterozoic IFs and secular evolution of sedimentary basins;
  • BIFs as bizarre or unusual rocks - presence in stratigraphic record


Iron-formation (IF) is an iron-rich (±30% Fe) and siliceous (±50% SiO2) sedimentary rock which results from extreme compaction and diagenesis of a chemical precipitate in which those components were major constituents. It is widely, but irregularly, distributed within Precambrian volcano-sedimentary successions. During most of the period from c.3.8 Ga until c.2.4 Ga IF was formed in greenstone successions, in relatively thin, tectonically deformed and metamorphosed units whose poor preservation makes the nature of their deposition uncertain. A number of major IF units of the Gondwana continents deposited in the later part of that period are better preserved, thicker and more areally extensive, and occur within successions whose depositional environments can be interpreted with more confidence. The IF of those units, and of all older IFs, has a centimetre-scale alternation of iron-rich and silica-rich bands (mesobands) whose presence justifies its usual designation as banded iron-formation (BIF); characteristically, the mesobanding of BIF has a high degree of lateral stratigraphic continuity. By contrast, the IF typically represented in the circum-Ungava belt of North America is not only significantly different in sedimentological characteristics but also younger (c.1.8 Ga). Although it is also banded, the banding is coarser and less regular that that of BIF, and the material of the bands is often finely granular. The name granular iron-formation (GIF) distinguishes it from the typical BIF of earlier sequences. Following deposition of these there is a hiatus in IF deposition until the later Neoproterozoic. The BIFs of the c.2.6–2.45 Ga Hamersley Group of Western Australia are by far the largest (in terms of contained iron), most extensive and thickest known, only the roughly coeval and lithologically near-identical BIFs of the Transvaal Supergroup of South Africa rivalling them in these respects. The Hamersley BIFs are therefore taken as archetypes for comparison with others. The mainly older (c.3.8–2.5 Ga) BIFs of greenstone belts are sufficiently similar to suggest that they have the same origin. The formation of such BIFs by precipitation of dissolved deep ocean ferrous iron by photosynthesizing organisms is consistent with all available evidence; and geochemical evidence is consistent with the mantle as an iron source for the oceans. The necessary and sufficient conditions for the deposition of BIF are the formation of depositories which: (i) remained tectonically stable for periods approaching 106 years; (ii) were deep enough both to avoid contamination with epiclastic material and to be free of bottom disturbance; and (iii) had dispositions such that deep ocean water was able to circulate freely into and out of them. Control of the time-distribution of Precambrian IFs solely by abrupt steps in biochemical evolution, closely linked to the increasing oxygen content of the atmosphere, cannot now be totally accepted; although aspects of Preston Cloud';s model proposing this are believed to remain valid, particularly his enthusiasm for a biogenic involvement in IF deposition. An additional factor controlling the early distribution of BIFs is thought to be the evolving architecture of volcano-sedimentary depositories related to the evolution of continental crust, a new model for which is outlined. The late Archaean peak of BIF deposition can be interpreted, to the extent that its existence is real, by gradually increasing tectonic suitability of depositories for BIF deposition as the structure of continents evolved. IFs are unusually sensitive indicators of depositional environment. Their distribution in the Precambrian stratigraphic record indicates that, from a sedimentological viewpoint, conditions on the Precambrian Earth were sufficiently different from those now obtaining to make the simplistic application of uniformitarian principles misleading.