The Winfield Formation, also known as the Winfield limestone, is a geologic formation in Nebraska and extends into Kansas and Oklahoma. It preserves fossils dating back to the Early Permian period.
Brachiopods make up most of the fossils in the Winfield formation, https://www.kgs.ku.edu/General/Geology/Clay/06_rock.html with genera such as Composita being especially common. Some of the other genera present are Derbyia and Juresania. also present but less common is the small Trilobite, Ditomopyge.
Other invertebrate fossils include Fusulinids, Crinoids, Bryozoans, Corals, and a mollusk, Aviculopecten.
See also
List of fossiliferous stratigraphic units in Nebraska Paleontology in Nebraska
References