A New Depositional Framework for Massive Iron Formations after The Great Oxidation Event

Abstract

Abundant global oxygen is crucial for macroscopic life on Earth today, yet the tempos and triggers of ancient oxygenation are unknown. Iron formations (originally defined as rocks with >15 wt. % iron; James, 1954) hold important clues to the early evolution of Earth's atmosphere and biosphere, yet questions about their genesis remain. In particular: (a) are all massive iron formations (IFs) deposited in broadly similar depositional and geochemical settings; and (b) what drives their episodic deposition? The purpose of this work is to assess these questions with a case study coupling facies-based sedimentological and stratigraphic approaches for the ∼1.88 Ga Gogebic Range exposed near Lake Superior, USA (Michigan-Wisconsin), one of a few preserved post-Great Oxidation Event (GOE) massive iron deposits.Massive IFs (∼10 6 Gigatons) occur only in the Precambrian (e.g., Bekker et al., 2014;Konhauser et al., 2017). When examining the geologic record, the largest volumes of preserved IFs span the Late Archean to