355 Frasnian Rugose Corals from Lime Creek and Shell Rock, Iowa

Rugose corals from Frasnian Lime Creek (“Hackberry”) and Shell Rock strata are known largely from the works of Fenton and Fenton (1924) and Belanski (1928, 1928), each of which described outcrop stratigraphy and major parts of the fauna. The Shell Rock Formation includes three members, two of which contains rugosans, the basal Mason City and the uppermost, or Nora Member. The overlying Lime Creek Formation contains the Juniper Hill Member, lacking corals, overlain by the very fossiliferous Cerro Gordo Member, source of much of the famous “Hackberry” coral fauna described by Fenton and Fenton in 1924. The uppermost, Owen Member, also contains abundant Rugosa. Based on the brachiopod and conodont zonation, the Shell Rock and Lime Creek coral faunas are middle and late, but not latest, Frasnian.