Gunflint Chert

The Gunflint Chert is a sequence of banded iron formation rock of the Animikie Group, exposed along Lake Superior's north shore across the Gunflint Range of northern Minnesota and northwestern Ontario, with its type locality near Schreiber, Ontario. It dates to the Paleoproterozoic, its host rock about 1.88 billion years old with contained microfossils reported across a broader 1.9 to 2.3 billion year range based on uranium-lead dating of interbedded ash layers, and consists of alternating iron-rich layers of hematite, magnetite and ilmenite with silica-rich layers of cryptocrystalline quartz as chert or jasper. Its black chert bands preserve exceptional microfossils of cyanobacteria-like organisms forming stromatolites, a discovery in the 1950s that provided some of the first scientific evidence of Precambrian microbial life and is sometimes called the first Precambrian lagerstatte.