Archean stromatolites from the Hartville Uplift, eastern Wyoming
Stromatolites occur in dolomitic marbles of two formations of the Whalen Group, which is cut by a 2.58-Ga-old granite. The lower part of the Whalen Group contains poorly exposed mounds as much as 18 m in width and up to 2 m in growth relief. These mounds are similar to those of Hadrophycus immanis from the Nash Fork Formation of the Medicine Bow Mountains 200 km to the southwest, which is generally considered to be early Proterozoic in age. Stromatolites that are exposed in the upper part of the Whalen Group are small- and medium-sized stratiform, columnar-stratiform, and branching columnar-stratiform types attributable to the long-ranging groups Stratifera , Collumnaefacta , and Gruneria . These are only the fifth and sixth Archean occurrences to be reported from North America.