The Atokan Stage (pennsylvanian): A Review: A Review

The Atokan Stage was the last of the five North American provincial stages of the Pennsylvanian to be named, and for a time it competed with three rival units, the Bendian, Lampasan, and Derryan. The Atokan type area, in southeastern Oklahoma, is ill-suited to represent a chronostratigraphic unit. These rocks are poorly exposed, structurally complicated, highly variable laterally, sparsely fossiliferous, and commonly unconformable to neighboring units. Proposed boundaries of the Atokan have been based on fusulinids and, to a lesser extent, on conodonts and ostracods. However, paleontologists disagree over zonation and where to place the boundaries. An Atokan symposium in 1984 detailed the problems and proposed solutions, but none of these seem to have taken hold. The need for appropriate definition of the Atokan Stage is obvious. We propose that the boundaries of Atokan follow the traditional fusulinid-based definitions, so that the base of the Atokan is the first appearance datum (FAD) of Eoschubertella and the top of the Atokan (base of the Desmoinesian) is the FAD of Beedeina. We favor a basal Atokan boundary stratotype section at Arrow Canyon, Nevada, and a basal Desmoinesian boundary stratotype in the Derry Hills, New Mexico.