Gunflint Chert

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The Gunflint chert is a sequence of banded iron formation rocks that are exposed in the Gunflint Range of northern Minnesota and western Ontario along the north shore of Lake Superior. The black layers in the sequence contain microfossils that are 1.9 to 2.3 Billion years in age. Stromatolite colonies that have been converted to jasper are found in Ontario. The formation consists of alternating layers of iron oxide rich layers interbedded with silica rich zones. The iron oxides are typically hematite or magnetite with ilmenite while the silicates are predominantly cryptocrystalline quartz as chert or jasper along with some minor silicate minerals.

Stanley Tyler in 1953 examined the area and noted the red stromatolites. He also sampled a jet-black chert layer which when observed petrographically revealed some small spheres, rods and filaments which were less than 10 micrometres in size. Elso Barghoorn, a paleobotanist at Harvard, looked at the samples and stated they were indeed structurally preserved unicellular organisms.[1] In 1965 the two published their finding and named a variety of organisms from the Gunflint. This created a rush to explore Precambrian fossils from similar environments.

[edit] References

• Barghoorn, E.S. and Tyler, S.A., 1965: Microorganisms from the Gunflint Chert. Science, vol. 147, p. 563-577.
• Schopf, J.W., 1999: Cradle of Life: The Discovery of Earth's Earliest Fossils. Princeton University Press, 336 p. ISBN 0-691-00230-4
• Superior type Banded Iron Formation
• Gunflint Chert