Iron-oxidizing microbial ecosystems thrived in late Paleoproterozoic redox-stratified oceans

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…1.88 Ga in basins having varied redox conditions and a strong redoxcline separating an upper oxic water column from deeper waters that were suboxic to anoxic (Planavsky et al, 2009). These ranges are similar to those seen in modern anoxic basins.…”

“…1.88 Ga Gunflint-type microfossils from the Animikie Basin have been reinterpreted as chemolithoautotrophic Fe(II)-oxidisers (Golubic and Lee, 1999;Planavsky et al, 2009). It is important to note that some Gunflint fossil groupings (e.g., Gunflintia) may encompass multiple types of bacteria, including those with different metabolisms (Shapiro and Konhauser, 2015).…”

Fossilized iron bacteria reveal a pathway to the biological origin of banded iron formation

“…Heavy rare earth element (REE) enrichment occurs in both the ferruginous and siliceous components of the rock relative to light REE (Fig. 3b) and is comparable to reported Precambrian BIF profiles [17][18][19] . Together with a pronounced positive Eu anomaly, these observations hint at a hydrothermal origin of the deposits as opposed to seawater-derived sediments that are often light REE-enriched relative to heavy rare earth elements 18 .…”

“…Similar to Precambrian BIFs, silica/iron ratios in these rocks are inversely related (Fig. 3a), while a low range of TiO 2 , Al 2 O 3 and K 2 O concentrations suggest little terrigenous sedimentary input [17][18][19] . Heavy rare earth element (REE) enrichment occurs in both the ferruginous and siliceous components of the rock relative to light REE (Fig.…”

“…Together with a pronounced positive Eu anomaly, these observations hint at a hydrothermal origin of the deposits as opposed to seawater-derived sediments that are often light REE-enriched relative to heavy rare earth elements 18 . Calculated Eu/Eu* and Ce/Ce* anomalies (North American Shale Composite (NASC) normalized) of B0.23 and B2.56, respectively, lie within the reported Precambrian BIF range, while Ce depletion in relation to the other REEs supports anoxic depositional conditions [17][18][19] . Sedimentary Ce levels are generally expected to increase under oxidizing conditions because, unlike most REEs, Ce 3 þ is oxidized to Ce 4 þ and coprecipitated in association with iron oxyhydro(oxides) [17][18][19] .…”