The Imo Formation, or Imo Shale, is a geologic unit in northern Arkansas that dates to the Chesterian Series of the late Mississippian. The Imo is considered to be a member of the upper Pitkin Formation, and is the most recent Mississippian age rock in Arkansas. The Imo Shale unconformably underlies the Pennsylvanian age Hale Formation
The stratigraphic placement of this interval has long been debated. It was introduced in 1964 as the "Imo Formation," representing an interval of shale that was presumably of Mississippian and possibly of Pennsylvanian age. However, in a footnote in the first publication to use this designation, the author noted that the shale interval had been mapped into the Pennsylvanian Cane Hill Member of the Hale Formation and revoked use of the name "Imo Formation".
The name was reintroduced in 1973 as the "Imo Shale", and in 2010 was classified as a member of the Mississippian age Pitkin Formation.
Paleontology Cephalopods
Anthracoceras A. discus Cravenoceras C. mapesi Delepinoceras D. bressoni Eumorphoceras E. imoense E. richardsoni Fayettevillea F. bransoni F. friscoense
Metadimorphoceras M. saundersi Peytonoceras P. ornatum Rhadinites R. miseri Somoholites S. cadiconiformisj Stenoglaphyrites S. involutum Syngastrioceras S. imprimis
Flora Stacheoides S. tenuis
Foraminifera Earlandia Endothyra Eosigmoilina E. explicata E. rugosa Monotaxinoides Neoarchaediscus Priscella Trepeilopsis Zellerina Z. discoidea
Ostracods Cavellina Cornigella Gortanella Healdia Healdioides Hollinella Monoceratina Sargentina Youngiella
See also
List of fossiliferous stratigraphic units in Arkansas Paleontology in Arkansas
References