Abstract:

Banded-iron formations (BIFs), typically consisted of interbanded iron- and silica-rich layers, are unique iron-rich sediments precipitated by extensive Fe(II) oxidation in the anoxic-hypoxic ocean during the Early Precambrian Era (mainly 3.8-1.8 Ga). The most abundant iron-containing minerals in BIFs are magnetite and hematite. BIFs provide the largest iron source to form giant iron ores that are of great economic value. Furthermore, as BIFs are closely related to the two billion-year co-evolution of life and earth environments, they are unique geological records for studying the important evolutionary events (e.g., the rise of atmospheric O₂) on the early Earth. However, few modern BIF analogues have been discovered due to the uniqueness of the Early Precambrian paleomarine environment and sedimentary conditions. Thus, there are still many unsolved mysteries about the origin of BIFs, despite intensive research in the past century. Among them, the most critical scientific question is how the dissolved Fe(II) was oxidized to form specific mineral assemblages in the anoxic paleo-ocean. In this review, the basic information on BIF types, material compositions and sources, as well as sedimentary conditions are summarized, followed by the proposed mechanisms of Fe(II) oxidation and their inherent problems from the perspective of special sedimentary environment of BIFs. Also discussed are the contribution of microbial-mediated nitrogen biogeochemical cycle to Fe(II) oxidation and the formation of BIFs and related research progress. Lastly, an outlook on the genetic study of BIFs is discussed.

Key words: banded iron formation, biogenesis, Fe(II) oxidation mechanisms, Fe(II) oxidation coupled with nitrogen cycle