Nankoweap Formation [SEP] named after
thin sequence of red beds unconformably overlying basaltic flows of the Unkar Group as a separate stratigraphic unit, which he called the “Nankoweap Group.“
Although more extensive outcrops exist in Basalt Canyon, Comanche Creek, and Tanner Canyon, it is named for a small, fault-bounded block of the Nankoweap Formation in Nankoweap Canyon. It was argued that these redbeds belonged neither to the underlying Unkar Group nor overlying Chuar Group. Maxson in his geological mapping reduced the Nankoweap Group to formational rank because the Nankoweap had not been
faulted Nankoweap Formation is a prominent angular unconformity that is part of the Great Unconformity.
Uranium-lead dating of detrital zircons from the Nankoweap Formation indicate the presence of zircon grains in approximately the 800-770 Ma age range. This finding indicates that the Nankoweap Formation is closely related in age and stratigraphy to the Chuar Group – and any unconformity associated with its upper contact is relatively minor in duration and significance. Thus, the Nankoweap Formation is most likely the basal unit of the Chuar Group.
Depositional environments.