How does Arbuckle limestone affect Oklahoma foundations?
In short: The Arbuckle carbonates are thick, hard limestone and dolomite beds that reach the surface in the Arbuckle Mountains of south-central Oklahoma. Where they are at the surface, houses often sit on or near firm rock, but the rock can dissolve slowly and form karst features such as small cavities and springs. Shallow rock and karst, not clay swell, are the main foundation questions in this setting.
What is the Arbuckle rock?
Carbonate rock means limestone (calcium carbonate) and dolomite (calcium-magnesium carbonate). The Arbuckle rocks were deposited in shallow seas 4. A century-old USGS survey of the area described the Arbuckle limestone as mostly hard bluish-white and cream-colored limestone and dolomite, with some clay beds and with chert and limestone breccia in places 3. It reported a maximum thickness of nearly 5,500 feet, with the lower part Cambrian and the upper part Ordovician 3.
The Arbuckle Mountains were pushed up about 315 million years ago, and the tilted limestone beds now form rows of outcrops sometimes called "tombstone topography" 4.
Arbuckle and Simpson together
Hydrologists group the Arbuckle with the overlying Simpson Group as the Arbuckle-Simpson aquifer. It underlies more than 500 square miles of south-central Oklahoma and supplies drinking water to about 39,000 people, including Ada and Sulphur 1. The rocks are limestone, dolomite and sandstone of Cambrian and Ordovician age, exposed in three uplifts separated by large faults 1. A USGS model describes the units as highly faulted and fractured and includes 54 faults in its study area 2.
What is karst?
Karst is ground shaped by rock that dissolves in water, producing features such as cavities, sinkholes, caves, disappearing streams and springs. The Oklahoma Geological Survey identifies the Arbuckle Mountains in the south and the Ozark area in the northeast as the state's main limestone and dolomite karst areas 5. It lists sinkholes, caverns, subsidence and collapse as potential hazards in karst terranes 5.
In the Arbuckle-Simpson outcrop, small karst features occur over much of the area, while caves large enough for people to enter are known at only a few locations 1. Springs discharge up to 19,000 gallons per minute and feed stream flow 1.
What does Arbuckle rock mean for foundations?
| Ground condition | Why it matters |
|---|---|
| Hard rock at or near the surface | The rock is described as uniformly hard 3 and crops out at the surface 4 |
| Fractures and faults | The units are highly faulted and fractured 2, and small karst features occur over much of the outcrop 1 |
| Small karst openings | Sinkholes and caves can let the ground settle or collapse 5 |
| Uplifted, tilted beds | Limestone layers dip down into the ground, forming tombstone topography 4 |
- On this ground, the key questions are what lies directly under the footing (sound rock, soil, or a soil-filled opening) and whether roof or yard water is being concentrated into fractures in the rock.
- Sudden, localized drops are a sign worth separating from slow seasonal movement. See sudden depressions or sinkholes and karst subsidence.
- Because contaminants can move quickly through karst 5, roof and surface drainage that is directed into open rock can also carry contaminants to groundwater.
How is deep Arbuckle rock tied to earthquakes?
The same rock group extends deep underground in other parts of Oklahoma. That deep setting is discussed separately in induced seismicity in Oklahoma and seismic damage vs. soil movement.
Where can I read more?
The South-Central (Arbuckles and Texoma) region page covers the soils and other rock units around the Arbuckle uplift, and gypsum karst and sinkholes explains the different, faster-dissolving karst of western Oklahoma.
Related
- Karst subsidence and sinkholes
- South-Central (Arbuckles and Texoma)
- Oklahoma geologic provinces
- Gypsum karst and sinkholes
- Void and compaction grouting
Common questions
What are the Arbuckle carbonates?
They are thick beds of limestone and dolomite laid down in shallow seas during the Cambrian and Ordovician periods. They are exposed at the surface in the Arbuckle Mountains of south-central Oklahoma.
Are there sinkholes in the Arbuckle Mountains area?
The Arbuckle Mountains are one of the two main limestone and dolomite karst areas in Oklahoma. Small karst features are found across much of the outcrop, but large open caves are known in only a few places.
Is the rock close to the surface?
In the outcrop belt the rock is uniformly hard and crops out at the surface, where tilted limestone layers form rows of outcrops sometimes called tombstone topography.
How does Arbuckle rock relate to Oklahoma earthquakes?
The deep Arbuckle Group is a separate topic from the surface outcrop. See the induced seismicity guide for how deep rock layers relate to Oklahoma earthquakes.
Sources
- Karst Aquifers: Arbuckle-Simpson Aquifer U.S. Geological Survey
- Three-dimensional geologic model of the Arbuckle-Simpson aquifer, south-central Oklahoma (Open-File Report 2010-1123) U.S. Geological Survey
- Description of the Tishomingo Quadrangle (Geologic Atlas Folio 98) U.S. Geological Survey
- The Oklahoma Geological Survey and the geology of Oklahoma USGS National Geologic Map Database (DMT '25)
- Mapping of Karst Terranes in Oklahoma to Identify Potential Environmental and Hydrologic Problems AAPG Search and Discovery / Oklahoma Geological Survey
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