Stromatolitic chert

Photograph by James Kocher.

Photography contest, Honorable Mention.

Slice of Gunflint Chert
Digitate stromatolites in the Gunflint formation (Lower Algal Member), Nolalu, Ontario. Mr. Kocher writes, "Specimen is a vertical section cut on lapidary saw (i.e., perpendicular to bedding). Thin piece (1-2 mm thick) is translucent chert and shows preserved columnar algal colonies, hematite oolites, and algal pellets (peloids). Specimen is ~4 cm wide. Variously classified as Collenia undosa, Stratifera biwabikensis, among others. Age ~ 1.8 Ga; Mesoproterozoic." Mr. Kocher explains further, "'Lower Algal Member' is a designation given to a subset of strata within the Gunflint Formation. The Gunflint Formation has been divided up stratigraphically into at least 5 subsets of strata, i.e., 'Members.'" Perhaps it goes without saying, but the specimen is flat, despite the illusion of hills and valleys.