A model for the deposition of the microbanded Precambrian Iron Formations.

Abstract

The proposed model defines the microbanding of the iron formations as the product of annual cycles of initial precipitation of Fe minerals, followed by precipitation of chert from evaporating stream-waters in non-marine basins in a low oxygen environment. Various lines of evidence, assumptions, and constraints are reviewed. The striking textural similarity of Australian Precambrian iron formation microbands with carbonate-anhydrite varves of the Permian Castile formation of west Texas-New Mexico lends support to the evaporite aspect of the model. -M.S.