Reassigned from member of Cedar Valley Formation to Coralville Formation, 1 of 4 formations of Cedar Valley Group (revised). Divided into Gizzard Creek (named) and Iowa City (named) Members in northern IA and Cou Falls (named) and Iowa City Members in eastern IA on Iowa shelf. Gizzard Creek extends into southeast MN (Iowa shelf) and northern MO (Lincoln anticline). Cou Falls extends into northeast MO (Lincoln anticline) and western IL (Wisconsin arch, Illinois basin). The lower fossiliferous parts with abundant marine fauna belong to Gizzard Creek and Cou Falls. The upper carbonate-dominated, laminated, brecciated, or evaporitic part with some restricted marine fauna belong to the Iowa City. Was deposited during a single transgressive-regressive cycle. Bounded by disconformities or discontinuities. Overlies, in northern IA, Hinkle Member (named) of Little Cedar Formation (named), basal formation of Cedar Valley Group. Overlies Rapid Member (named) of Little Cedar Formation in eastern IA. Underlies Osage Springs Member (named) of Lithograph City Formation (named) of Cedar Valley in northern IA, and State Quarry (rank reduced) or Andalusia Member (named) of Lithograph City in eastern IA. Nomenclature charts. Graphic sections. Cross section. Of Middle Devonian, late Givetian age. These rocks formerly designated unit B of Cedar Valley Group, or part of Coralville Member of Cedar Valley Formation.

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