PERMO-CARBONIFEROUS VERTEBRATE FOSSILS FROM THE HALGAITO SHALE, CUTLER GROUP, SOUTHEASTERN UTAH
The Early Permian Cutler Group, spanning northeastern Arizona to southeastern Utah, west of Comb Ridge, San Juan County, Utah, has been divided into four formations. From oldest to youngest these formations are the Halgaito Shale, the Cedar Mesa Sandstone, the Organ Rock Shale, and the DeChelly Sandstone. The Halgaito Shale rests unconformably on the Late Pennsylvanian Honaker Trail Formation of the Hermosa Group. Although there are local unconformities between the Cutler and Hermosa groups, recent biostratigraphic studies have suggested that the basal portion of the Halgaito Shale in the area of Glen Canyon National Monument (GCNM) spans the Permo-Carboniferous boundary.
Recent finds from GCNM represent the first recorded locality from the Halgaito Shale inside the monument. Here, the Halgaito is characterized by fine grained red sands, typically in aeolian depositional structures. Fossils are primarily recovered from small channels of limestone, pebble to cobble conglomerates. As such, fossils occur as isolated bones and fragments; diagnostic material is extremely rare. The GCNM locality has produced remains of both freshwater aquatic and terrestrial vertebrates. These fossils along with others collected from adjacent valleys (including Johns Canyon and the Valley of the Gods) are currently under study at CSUSB.