Seven Rivers Formation

The Seven Rivers Formation is a geologic formation in southeastern New Mexico and west Texas. It preserves fossils dating back to the late Guadalupian Epoch of the Permian period.

Description
The formation consists of 400-1970 feet of anhydrite, with interbeds of shale, dolomite, siltstone, and sandstone. It rests on the Queen Formation and is overlain by the Yates Formation. The Seven Rivers Formation is part of the Artesia Group, which is interpreted as a sequence of shelf rocks of the Capitan reef.

History of investigation
The unit was first named as the Seven Rivers Member of the (now abandoned) Chupadera Formation by Oscar Edward Meinzer and coinvestigators in 1927. In 1937, W.B. Lang assigned the Seven Rivers Member to the (now abandoned) Chalk Bluff Formation and removed its upper beds to the Three Twins Member. The unit was promoted to formation rank and assigned to the Whitehorse Group by Ronald K. DeFord and E. Russel Lloyd in 1940. Norman D. Newell and coinvestigators assigned the formation to the (now abandoned) Carlsbad Group in 1953, and it was assigned to the Artesia Group by D.B. Tait and coinvestigators in 1962.