Mineralogy of Eocene Fossil Wood from the “Blue Forest” Locality, Southwestern Wyoming, United States

Central Wyoming, USA, was the site of ancient Lake Gosiute during the Early Eocene. Lake Gosiute was a large body of water surrounded by subtropical forest, the lake being part of a lacustrine complex that occupied the Green River Basin. Lake level rises episodically drowned the adjacent forests, causing standing trees and fallen branches to become growth sites for algae and cyanobacteria, which encased submerged wood with thick calcareous stromatolitic coatings. The subsequent regression resulted in a desiccation of the wood, causing volume reduction, radial fractures, and localized decay. The subsequent burial of the wood in silty sediment led to a silicification of the cellular tissue. Later, chalcedony was deposited in larger spaces, as well as in the interstitial areas of the calcareous coatings. The final stage of mineralization was the precipitation of crystalline calcite in spaces that had previously remained unmineralized. The result of this multi-stage mineralization is fossil wood with striking beauty and a complex geologic origin.