Interesting Ventifacted Green River Eocene Stromatolite

Not only are these Green River stromatolites quite striking, they are interesting from several perspectives: Coming from the Eocene Green River shale formed fromed in a fresh-water aquatic ecosystem, it is young for stromatolites. Thus, photosynthetic, eukaryotic algae are more likely to have been the organisms responsible, as opposed to photosynthetic, prokaryotic cyanobacteria. But, this cannot be confirmed, and it is also possible that both types of organisms were involved in building the contrasting laminae. It is composed of chert, or cryptocrystalline quartz, a commonly found mineral form of stromatolites. This material is also known as flint. This particular flint was found in a bed of debris that was once used by primitive Native Americans to make tools or perhaps arrowheads. This, there is an archeological spin to its history. Finally, note the polished appearance of the surface. In fact, it is naturally polished, apparently by extended exposure to wind-driven sand, a process known as ventifaction.