Rare Gunflint Stromatolite

This stromatolite is from the Gunflint Formation, a Paleoproterozoic chemical-clastic sedimentary assemblage outcropping to the immediate northwest of Lake Superior that became famous in 1954 as containing the oldest fossil assemblage known at that time. Older microfossils have since been discovered, but the Gunflint prokaryotes remain one of the most diverse Precambrian fossil communities. In the March 7, 2002 edition of Nature (Volume 406), J.W. Schopf, himself famous for his role in the discovery of Domain of Life Archaea, reported discovery of cellular remains of prokaryotic cells in the Gun Flint stromatolite (combining optically discernible morphology with analyses of chemical composition, laser-Raman spectroscopic imagery). His results remain controversial, however. At about the same time, the age was measured at 1.9 billion years.

Note the intricate domal layers of this chertized (Chert is cryptocrystalized quartz) stromatolite that represents a piece of history in the study of Pre-Cambrian paleobiology.