Named as middle formation (of 3) in the northern area of the Sapulpa group; named from Curl Creek, Nowata Co, OK on the Chautauqua platform. No type locality designated. Occurs in a broad, conspicuous band from the KS State line near Coffeyville south and somewhat west past Lenapah, Delaware, Nowata and Oglesby to the west-central part of the Nowata quad; area of occurrence averages about 6 mi wide, maximum being 10 mi. Consists, in the lower part, of a mass of homogeneous bluish or greenish clay shale which weathers yellow or greenish. Consists, in the upper part, of sandstones appearing just south of the KS State line and increasing in thickness southward; these sandstones together with the Hogshooter limestone member (new), basal member of Wann formation, form the prominent scarp lying at or near the western limit of outcrop. Thickness of the Curl formation is about 300 ft from the northern OK State line south to the latitude of Nowata or beyond; in southern part of Nowata quad, thickness is somewhat more than 300 ft. Overlies Lenapah limestone (new) and underlies Wann formation (new), both of the Sapulpa group. Stratigraphic chart. Correlates with the Pleasanton shales, Bethany Falls limestone, Ladore shales, Mound Valley limestone, Galesburg shales, Dennis limestone, and Cherryvale shales of KS. Of Pennsylvanian age.

Source: GNU records (USGS DDS-6; Denver GNULEX).