Archaean Stromatolites from Wyoming

There are but few Archaean stromatolites sites in North American, making this an unusual specimen. Clearly much of the ancient reefs have been ground up into sediment, and perhaps much subsumed back into the Earth's mantel. These stromatolites come from the Hartville Uplift that is cut by a granite dike radio-dated at 2.58 billion. This stromatolite comes from below the granite and is therefore older. Being dolomite that has been highly metamorphosed, it fits into the Stratifera form genera.

Some theories hold that stromatolites were widespread and prolific reef builders in the Archaean and through the Lower Proterozoic, and steeply declined beginning by the Middle Proterozoic. The primary microorganism that built stromatolites is believed to have been photosynthetic Eubacteria that oxygenated the earth’s oceans and atmosphere.

This specimen is unique in another respect. As the back-lighted top right picture shows, calcite crystal is tranlucent in some areas, creating a bit of a light show.