Geologic Mapping Studies at Buffalo National River, Northern Arkansas

Science Center Objects

Detailed geologic mapping is being conducted by the USGS in and adjacent to the Buffalo National River, a park administered by the National Park Service, to better understand and characterize the natural resources and associated ecosystems of this area within the Ozark Plateau region. General-purpose geologic maps are created to provide a framework for a host of natural resource, natural history, and public education uses. The mapping activities focus on understanding development of karst features and ground water flow paths through extensive karst aquifers within Ordovician through Pennsylvanian rock strata that underlie the Buffalo River watershed.

The geologic maps provide background to understand major cave resources in the park, geologic controls on major spring locations, and recharge areas for springs, including recharge basins that extend beyond the surface watershed boundaries of the Buffalo River.

(Research funded by Geologic Framework of the Southern Ozark Plateaus Project, USGS National Cooperative Geologic Mapping Program and National Park Service Water Resources and Geologic Divisions)

 

Location of Buffalo National River in Arkansas

Figure 1. Location of Buffalo National River

Project Activities

  • Conduct geologic mapping at 1:24,000 scale of quadrangles in and adjacent to the Buffalo River watershed (fig. 2). As part of geologic mapping for each quadrangle, summarize the stratigraphic succession, document structural features, and develop a structure contour map for the major aquifer unit.
  • Construct and compile Geographic Information System (GIS) databases of the geologic data.
  • Integrate geology with National Park Sevice karst and spring inventories and dye tracer results to investigate geologic controls on karst hydrology.
  • Investigate Buffalo River landscape development through studies of karst features and surficial deposits (fig. 3).
  • Conduct three-dimensional modeling of geologic framework (fig. 4).

 

Map showing status of geologic mapping in western part of Buffalo National River

Figure 2. Status of Geologic Mapping in Western Part of Buffalo National River

 

Photo collage of karst features in Buffalo National River

Figure 3. Examples of karst features within the Buffalo National River Park. Karst is a type of topography that is formed over limestone, dolomite, or gypsum by dissolving or solution, and that is characterized by closed depressions or sinkholes, caves, and underground drainage (American Geological Institute Dictionary of Geologic Terms).

 

Model of 3D geology model of the western part of the Buffalo River area

Figure 4. Three-dimensional geology model of the western part of the Buffalo River area. View is toward the north and colors show different rock formations that are distributed across the area.

 

The geologic mapping helps place inventories of springs and caves within the park in proper stratigraphic context. Caves and springs are present in a variety of geologic formations ranging in age from Ordovician to Pennsylvanian, but they are concentrated within the 120-m-thick, Mississippian-aged limestone of the Boone Formation. Springs (fig. 5) in the western part of the park are most frequent near the unconformable contact between the basal St. Joe Member of the Boone Formation and underlying sandstone-rich Ordovician Everton Formation. These features indicate that the Boone Formation, comprising the karstic Springfield aquifer, is the principal path for ground-water flow into the western Buffalo River watershed. New mapping documents that major springs and cave systems are localized in structural lows (fig. 6) of the Boone Formation where ground water discharges at lowest elevations within the perched Springfield aquifer. Dye-tracer studies indicated that some springs localized in structural lows have captured recharge from beyond topographic watershed boundaries (fig. 7). This interbasin flow of ground water becomes a land management concern if agricultural land use of adjacent watersheds results in transfer of nutrient-enriched ground water in the Buffalo River.

Springs at Buffalo National River

Figure 5. Springs localized in basal St. Joe Limestone Member of Boone Formation, the principal karst aquifer of the western Buffalo River region.

Section of 3D model of springs, Buffalo National River

Figure 6. Three-dimensional model of geology showing major springs localized at base of structural low in Boone Formation.

 

Map of dye tracer study of Dogpatch Springs interbasin recharge area

Figure 7. Dye tracer study of Dogpatch Springs interbasin recharge area. Discharge springs are localized at corner of structural low formed by intersection of two faults.

New geologic mapping in the middle part of the Buffalo River documents a transition from the Springfield Plateau aquifer to lower karstic Ordovician formations of the Ozark aquifer. The largest spring in the park, Mitch Hill Spring (fig. 8), discharges from a stratigraphic level in the lowest part of the Ordovician Everton Formation above impervious argillaceous dolostone of the Powell Dolomite that is brought to the surface along the Buffalo River in a structural high. Dye tracer studies integrated with the geologic mapping are investigating probable pathways for ground water between the two aquifers.

Mitch Hill Spring with tracer dye path arrows

Figure 8. Black arrows represent general paths of tracer dye to detection sites.

New geologic mapping has recognized many new faults and folds in the region and has added information on the age and character of new and previously recognized faults. These data are revealing new insights into the ancient history of deformation in the area that was probably related to past interactions among tectonic plates in late Paleozoic time.

Results of these mapping efforts were presented to fieldtrip participants at the Geological Society of America North Central/South Central section combined meeting in April 2010. Mark Hudson and Kenzie Turner of the USGS and Chuck Bitting of the National Park Service led the field trip to emphasize geologic controls on karst development in the Buffalo National River area (fig. 9).

Fieldtrip stop in Buffalo National River

Figure 9. Field trip leaders describe the geologic controls on the formation of the large sinkhole in the Batesville Sandstone.