Iron Formation

Iron Formation

Volcanic ventings on the seafloor introduced iron into early sea water allowing formation of iron-silica particles that remained suspended in the ocean for extended periods of time. Their precipitation in quiet, deep-marine settings formed chert-magnetite, sometimes with iron-rich clays (greenalite).

Magnetite-chert iron formation.

Magnetite-chert iron formation: between mafic volcanic flows.

Magnetite-Greenalite: magnetite-chert iron formation interlayered with green, iron-rich clay (greenalite).

Greenalite-Magnetite: folded steel-grey magnetite and bright green, iron-rich clay (greenalite).

Magnetite iron formation: beds of magnetite interlayered with siltstone (clastic input).

Fun Fact: iron-silica particles suspended in ancient oceans were an ancient sunscreen for early marine organisms (cyanobacteria), protecting them from lethal effects of direct UV exposure. These early organisms generated oxygen through oxygenic photosynthesis, and their protection led to oxygenation of Earth's atmosphere, leading to evolution of oxygen-based respiration and multicellular organisms.