GEOLOGIC MAP OF THE CHICKASAW NATIONAL RECREATION AREA, SOUTH-CENTRAL OKLAHOMA

The Chickasaw National Recreation Area (CNRA) is an important part of the Arbuckle-Simpson aquifer, a critical groundwater source for south-central Oklahoma. The CNRA also contains numerous freshwater and mineral springs that discharge in the Recreations Area’s Rock Creek and its principal tributary, Travertine Creek. The National Park Service (NPS) held a Geologic Resources Evaluation scoping meeting at the CNRA on October 17-18, 2007, to discuss the potential for mapping the Recreation Area at 1:24,000-scale and to conduct geophysical surveys in the northern part of CNRA’s Travertine area. Large-scale maps are extremely useful to resources managers as they capture most geologic features of interest and are spatially accurate within 12 meters. The NPS scoping meeting resulted in a USGS contract in April, 2008. The 1:24,000-scale USGS map identifies and revises numerous unit contacts and shows that some of the formerly undifferentiated rock units are locally mappable as individual formations. The map and map pamphlet includes two detailed cross sections that characterize the subsurface stratigraphy and fault structures for areas in, and just a few kilometers outside, the CNRA. The map pamphlet also includes information pertaining to how the geologic units and structural features relate to the formation of the Arbuckle Mountains and Arbuckle-Simpson aquifer. The use of a handheld computer in the field greatly increased both the accuracy and efficiency in completing the 1:24,000-scale map. Both ground audio-magnetotelluric and helicopter electromagnetic geophysical surveys complemented the geologic mapping by providing additional subsurface contact and fault control in the northern, central, and western parts of the CNRA.

Small circular-shaped hills that occur just east of the CNRA are similar to hills examined in other parts of the eastern Arbuckle Mountains. We interpret these hills or knobs to be the result of ancient karst-related collapse and subsequent erosion that exhumed large sink holes. The circular shape of these features and the inward dips of strata toward the hill’s axes collectively suggest that they initially formed as sag-like sink holes and that the collapsed rocks units were more resistant to erosion than were the surrounding rocks they collapsed into.