Ames
Key facts
- Country
- United States
- Diameter
- 16 km
- Age
- about 470 ± 30 million years
- Location
- 36.25° N, 98.20° W
Nothing: the crater lies about 3 km beneath the wheat fields of Major County, Oklahoma. Oil wells dot the area above it.
Ames is a buried impact crater about 16 km across in Major County, northern Oklahoma, in the United States. It is best known as one of the most productive oil and gas fields linked to an impact crater anywhere in the world.
What it hit. About 470 million years ago, in the Ordovician, an impactor struck a shallow sea floor of dolomite, a carbonate rock, overlying Precambrian granite. The blast excavated a crater with a raised rim and a central uplift of granite. The crater was soon buried by younger sediments, and today it lies about 3 km underground.
Discovery. The crater was found by accident in 1991, when an oil company drilled a well into what it expected to be ordinary rock and instead struck a thick layer of broken granite and dolomite, an impact breccia, which turned out to hold large amounts of oil. Further drilling and seismic surveys outlined the round structure. Cores from the wells contain quartz grains with planar deformation features, produced only by shock, together with impact melt rock.
Oil and gas. The broken and porous rock of the crater rim and floor makes an excellent reservoir, while the shales that filled the crater act as a seal on top. Hundreds of wells have been drilled, and the field has produced many millions of barrels of oil and large amounts of gas.
Why it matters. Ames transformed the oil industry's view of impact craters. After its discovery, companies began to look at buried craters as potential reservoirs. The impactor is unknown.
Did you know?
Ames was discovered in 1991 when an oil well hit broken granite instead of the expected rock.
It has produced many millions of barrels of oil.
The crater lies about 3 km beneath the surface.