Rock Point Formation


The Rock Point Formation is a geologic formation in New Mexico and Utah. It preserves fossils dating back to the late Triassic.

History of investigation

The unit was first named by Harshbarger, Repenning, and Irwin in 1957, who assigned Gregory's "A" division of the Chinle Formation to the Wingate Formation as the Rock Point Member. It was named for Rock Point School, located near the type exposures at Little Round Rock. Stewart et al. argued in 1972 that the unit has more affinity with the Chinle, and Dubiel assigned the Rock Point to the Chinle in 1989. The unit has created an unusual amount of controversy, but Lucas et al. raised it to formation rank within the Chinle Group in 2005.

Description

The formation is up to 70 m thick and is mostly reddish-brown and grayish-red massive siltstone and fine sandstone beds. It is the uppermost portion of the Chinle Group wherever it is exposed. In the Chama basin, its base is placed at the first persistent sandstone bed above the mudstones of the Petrified Forest Formation. Its contact with the overlying Entrada Sandstone is sharp.

Fossils

The famous Whitaker quarry of Ghost Ranch, New Mexico is believed to belong to the Rock Point Formation, although these beds have also controversially been assigned to the Owl Rock Formation. This quarry has also been referred to as the Coelophysis quarry due to preserving a large number of specimens of the early theropod dinosaur Coelophysis bauri.

Footnotes