Atokan

Atokan is a regional geologic stage used in North American stratigraphy to describe part of the Pennsylvanian subperiod of the Late Carboniferous. It is named after Atoka, Oklahoma, where representative rocks of this age were studied and correlated with other Pennsylvanian deposits. The Atokan is part of the sequence of North American stages that also includes Morrowan to its lower side and Desmoinesian to its upper side.

Geographically, the Atokan stage is most commonly applied to the midcontinent region of the United States, including parts of Oklahoma, Texas, Kansas, and surrounding areas, as well as adjacent sedimentary basins. The rocks assigned to the Atokan are typically part of cyclothemic sequences—alternating coal-bearing, paralic, and marine deposits—that reflect fluctuating sea levels and sediment supply characteristic of the Pennsylvanian world.

In terms of age and correlations, the Atokan sits after the Morrowan stage and before the Desmoinesian stage within North American practice. Its boundaries are defined in part by fossil assemblages, including conodonts, foraminifera, and plant remains, which help correlate rock units regionally and with global Pennsylvanian time scales. Because it is a regional stage, the exact age and lithologic expression of the Atokan can vary across local stratigraphic sections.

Subdivisions of the Atokan, where used, may include lower and upper intervals, reflecting internal changes in deposition and fossil content over time. In practical terms, the Atokan remains a key reference point for describing coal-bearing strata and sedimentary sequences in the central United States during the Pennsylvanian subperiod.