Three brachiopod faunas have been described from Lower Devonian strata in Oklahoma: Haragan-Bois d'Arc Formations of Helderbergian (Gedinnian) age, Frisco Formation of Deerparkian (Siegenian) age, and the Sallisaw Formation of early Onesquethawan (Emsian) age. Beds with the Haragan-Bois d'Arc fauna are confined to south-central Oklahoma, and those with the Sallisaw fauna to eastern Oklahoma. The Frisco fauna is distributed more widely, being present in strata which crop out in the Arbuckle Mountains of south-central Oklahoma and the Ozark region of eastern Oklahoma, and in the subsurface of central and southwestern Oklahoma. Cores from the central part of the state show Frisco strata with a well-developed Deerparkian brachiopod fauna resting on the Upper Silurian Henryhou e Formation bearing a fauna of pentamerid brachiopods. These two faunas make it possible to define the Silurian-Devonian contact with precision through a substantial area in the central part of the state. Frisco brachiopods also have been recovered from a core in southwestern Oklahoma where the Frisco rests on Ordovician strata. Oil production from the Devonian of central Oklahoma, notably the West Edmond field, is believed to be largely from the Frisco Formation.

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