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

The Arbuckle-Simpson aquifer in the Arbuckle Mountains of south-central Oklahoma is a critical ground-water resource. The current published maps showing the geology that confines the aquifer, in particular the water-producing rocks of the Hunton anticline area, were by William E. Ham, Myron E. McKinley, and Martin P. Gilbert at both 1:72,000 and 1:100,000 scales. All previous maps of Arbuckle geology were constructed using a drafted base, and the only published digital map is a 1:100,000-scale compilation by Cedarstrand published in the mid-1990’s. These geologic maps commonly combine numerous hydrologically-significant formations into one “undifferentiated” map unit. For example, the Ordovician- to Devonian-age Hunton Group consists of seven formations but is mapped as the unit “DSOh”. USGS reconnaissance mapping in 2008 also showed some inconsistencies including errors in fault and unit contact location and mislabeling.

After the USGS met with the National Park Service (NPS) Geologic Resources Evaluation group in October, 2007, the NPS concluded that Chickasaw National Recreation Area (CHIC) should be geologically mapped at 1:24,000 scale, and contracted with the USGS in April, 2008, to map CHIC. Mapping of CHIC is ongoing with completion expected at the end of 2009. Our new 1:24,000-scale mapping effort of CHIC thus far identifies and revises numerous unit contacts and faults and demonstrates that some of the “undifferentiated” rocks units are now mappable as individual rock units. For example, both the upper and lower Hunton Group exposures can be differentiated and the Sylvan Shale and Viola Group represent separate map units. In addition, a new waterborne electromagnetic geophysical survey of the Lake of the Arbuckles, planned for late August, 2009, will complement CHIC mapping by providing additional contact and fault control in the central parts of the map area.