| Flynn Creek crater | |
| Map: | United States#Tennessee |
| Confidence: | Confirmed |
| Age: | 360 ± 20 Ma |
| Exposed: | Yes |
| Drilled: | Yes |
Flynn Creek crater is an impact crater situated in Jackson County, Tennessee, approximately 8 km south of Gainesboro.
The impact crater was formed approximately 360 million years ago as a shallow, saucer-shaped crater, 3.8km (02.4miles) in diameter and about 150m (490feet) deep. A large central hill, highly deformed rim strata, and a breccia lens 40m (130feet) in thickness were produced during formation. Over 2km2 of flat lying Middle and Upper Paleozoic limestone and dolomite were brecciated and mixed to a depth of 200m (700feet), and at least half of the breccia was ejected from the crater. The remaining breccia contains fragments ranging in size from small grains to megabreccia blocks 100m (300feet) long. Undisturbed strata lie 100m (300feet) below the original crater floor.[1]
In the middle of the crater, a sequence of steeply-dipping, folded, faulted, and brecciated Middle Ordovician limestone and dolomite has been uplifted 100m (300feet) to form a large central hill. Rock of the Knox group in the central uplift are raised 250m (820feet) above their normal position and locally contain shatter cones.
In the rim surrounding the crater, Ordovician limestone has been uplifted NaNm (-2,147,483,648feet) and is moderately to tightly folded into doubly plunging anticlines and synclines that have axes concentric to the crater walls. In parts of the rim, folds have resulted in radial shortening as great as 35%. Faulting is common in the rim strata and is usually concentric to the crater walls.
In the southeastern rim, a large thrust block forms the crater wall and has been moved out from the crater and uplifted about 50m (160feet). The thrust block partly overrides a tilted rim graben that has down-dropped about 100m (300feet) and moved toward the crater. Overlying this graben is a layer of breccia which is apparently the remains of an ejecta blanket that once surrounded the crater.
Post-crater erosion removed the ejecta, except for the overlying graben, and lowered the regional ground surface less than 30m (100feet). Within a few million years of the cratering event the entire structure was covered with shale deposits from the Late Devonian Chattanooga Sea, creating one of the best-preserved ancient impact structures presently known. Subsequent erosion along Flynn Creek drainage has exposed a large extent of the structure. Karst development in the immediate area has created numerous caves associated with impact features, including the only cave known to occur in the central uplift of an impact structure, Hawkins Impact Cave.