image: This is a drill core of rocks recording deposition within Paleolake Nonesuch. view more
Credit: Image courtesy of Sarah P. Slotznick
Researchers report magnetic evidence of oxygenation in a lake during the Proterozoic Eon. In the early history of life on Earth, oxygenated terrestrial lakes may have represented refuges for the evolution of eukaryotic life, given that marine environments, particularly deep waters, were likely low in oxygen. The 1.1 billion-year-old Nonesuch Formation, on the shores of Lake Superior, has been interpreted as being deposited in a predominantly anoxic lake. Sarah P. Slotznick and colleagues analyzed two drill cores from the Nonesuch Formation spanning various water depths within the lake. The authors used magnetic data and explored the mineralogy of the drill cores to determine the mineral phases of iron, with different phases representing different degrees of oxygenation. Three distinct assemblages of minerals emerged, suggesting a gradient of oxygenation according to water depth. Reduced iron oxides in the deepest waters indicated anoxic conditions, but mid-depth waters contained magnetite and hematite, suggesting low oxygenation, whereas the shallowest waters contained only the most oxidized iron mineral, hematite. According to the authors, the results suggest the presence of at least some oxygen in most of the water column, and throughout most of the history, of the paleolake.
Article #18-13493: "Oxygenated Mesoproterozoic lake revealed through magnetic mineralogy," by Sarah P. Slotznick, Nicholas L. Swanson-Hysell, and Erik A. Sperling.
MEDIA CONTACT: Sarah P. Slotznick, University of California, Berkeley, CA; tel: 717-222-1022; e-mail: sslotz@berkeley.edu
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Journal
Proceedings of the National Academy of Sciences