Editing Banded iron formation (section)

====Absence of oxygen or hydrogen sulfide====
The absence of hydrogen sulfide in anoxic ocean water can be explained either by reduced sulfur flux into the deep ocean or a lack of [[dissimilatory sulfate reduction]] (DSR), the process by which microorganisms use sulfate in place of oxygen for respiration. The product of DSR is hydrogen sulfide, which readily precipitates iron out of solution as pyrite.<ref name="holland-2006"/>

The requirement of an anoxic, but not euxinic, deep ocean for deposition of banded iron formation suggests two models to explain the end of BIF deposition 1.8 billion years ago. The "Holland ocean" model proposes that the deep ocean became sufficiently oxygenated at that time to end transport of reduced iron. [[Heinrich Holland]] argues that the absence of [[manganese]] deposits during the pause between Paleoproterozoic and Neoproterozoic BIFs is evidence that the deep ocean had become at least slightly oxygenated. The "[[Canfield ocean]]" model proposes that, to the contrary, the deep ocean became euxinic and transport of reduced iron was blocked by precipitation as pyrite.<ref name="holland-2006"/>

Banded iron formations in northern [[Minnesota]] are overlain by a thick layer of ejecta from the [[Sudbury Basin]] impact. An [[asteroid]] (estimated at {{convert|10|km|abbr=on}} across) [[Impact event|impacted]] into waters about {{convert|1000|m|abbr=on}} deep 1.849 billion years ago, coincident with the pause in BIF deposition. Computer models suggest that the impact would have generated a [[tsunami]] at least {{convert|1000|m|abbr=on}} high at the point of impact, and {{convert|100|m|abbr=on}} high about {{convert|3000|km|abbr=on}} away. It has been suggested that the immense waves and large underwater landslides triggered by the impact caused the mixing of a previously stratified ocean, oxygenated the deep ocean, and ended BIF deposition shortly after the impact.<ref name="Slack_2009"/>