Stromatolites in Glacier National Park

May 19, 2017


Photographer: Rod Benson
Summary Author: Rod Benson

May 2017 Viewers' ChoiceFeatured above are fossil stromatolites found along the Highline Trail in Glacier National Park, Montana. The park is made almost entirely of rocks from the Belt Formation (also known as the Belt Supergroup) - layer upon layer of sandstones, shales and carbonates from the late Precambrian Era. At that time, there were no organisms with bones or shells, so stromatolites are the only fossils that can be found in Glacier Park. Fossils of different species of stromatolites can be found in different areas of the park.

Stromatolites are mound-like, multi-layered colonies of algae (blue-green algae or cyanobacteria), and their formation has much to do with the way they change the chemistry of the shallow water where they live. The photosynthetic cyanobacteria remove carbon dioxide from the surrounding water, causing calcium carbonate to precipitate onto their slimy, mat-like colonies. Calcium carbonate, along with grains of sediment (silt, etc.), sticks to the biofilm layer that covers the colonies. As the cyanobacteria continue to grow up through the sediment, a new layer forms. This process occurs over and over again, creating layered mounds, columns, or sheets.

Stromatolites that lived in the Precambrian played a major role in increasing the amount of oxygen in the atmosphere of the primeval Earth (The Great Oxygenation Event). It should be noted that living stromatolites can be found today at Shark Bay in Western Australia. Photo taken on August 30, 2014.

Photo Details: Camera: Panasonic DMC-LX7; Focal Length: 4.7mm (35mm equivalent: 24mm); Aperture: ƒ/2.8; Exposure Time: 0.0031 s (1/320); ISO equiv: 80; Software: QuickTime 7.6.6.