Iron formations: unique archives to reconstruct the Precambrian Earth

Iron Formations (IFs) are Fe- and Si-rich marine chemical sedimentary rocks that are confined to the Precambrian rock record. Although many aspects of IF depositional mechanism(s) are intensively debated and despite their diverse mineralogy, IF occurrences throughout the Archean, Paleoproterozoic and partly Neoproterozoic rock record have highlighted IFs as unique archives to unravel and reconstruct the coevolution and interactions of Earth's oceans, landmasses, atmosphere, and life through deep time. This chapter sheds light on the applicability of IFs as archives directly derived from the geological record to tackle diverse research questions in the interdisciplinary fields of biogeosciences. Here, the aim is to provide a general background in combination with recent advances on the classification of IFs, mineralogical as well as geochemical features, and proposed IF depositional models with a special focus on the Archean and early Paleoproterozoic. It also provides novel insights into which signatures are indicative of paleoenvironmental conditions or postdepositional modifications and describes the usage of IF as recorders for Earth's oxygenation, in particular covering the first dramatic increase in atmospheric oxygenation during the Great Oxidation Event (GOE) and subsequent changes of Earth's environments and ocean chemistry. This chapter also tackles the usefulness of IFs to gather information about the geodynamic evolution of early Earth from a seawater perspective. It also provides snapshots into the potential of IFs to reconstruct the elemental evolution and sources that affected and dominated ancient seawater chemistry in different IF depositional settings, with additional implications for the evolution of Precambrian habitats and life.