Revisions to the Wanakah Formation in and around Ouray County, Colorado

A well-defined type section and consistent nomenclature are fundamental requirements for successful correlation of stratigraphic units and subsequent accurate paleogeographic reconstructions. The exact location of the original type section of the Middle Jurassic Wanakah Formation of the eastern Colorado Plateau was found in Ouray County, Colorado. Two nearby reference sections are described that supplement the lithologic descriptions in the original type section. These reference sections and the original type section constitute a “principal reference section” for the Wanakah Formation. Informal names “upper shale beds”, “marl member”, and “beds at Sawpit” have been used to describe the uppermost member of the Wanakah. These terms are replaced with the formal name, “Crooked Tree Member of the Wanakah Formation”, in the reference sections to avoid confusion, foster consistent usage, and facilitate litho-stratigraphic correlation.