FLYNN CREEK IMPACT STRUCTURE

FLYNN CREEK IMPACT STRUCTURE

by: Charles O’Dale

  • Type: Complex
  • Age ma: 382.03 ± 0.21 a
  • Diameter: ~3.8 km
  • Location: N 36° 17 W 85° 40
  • Shock Metamorphism: shatter cones

a Dating Method: Geological – With some limitations, and acknowledging analytical error ranges of ±2 m.y. for published radiometric dates, as well as competing geochronological schemes … the 0.42 m.y. time interval from 382.24 to 381.82 Ma. (lower Frasnian) thus brackets the time of impact.

A generalized tectonic map of the southern interior lowlands of the United States which shows the locations of the Howell Structure and Nashville Dome with respect to three concentric faults (after Roddy, 1968: 293).
Areal geologic map of Flynn Creek area (Wilson and Born, 1936: 818)
East-west structural cross section of the Flynn Creek site (after Wilson and Born, 1936: 824).

Flynn Creek impact structure located in north-central Tennessee is a Late Devonian, 3.8-km diameter, complex, marine target impact crater, which formed in an epicontinental shelf setting. Flynn Creek is thought to be the result of an extremely shallow marine impact that occurred in perhaps 10 meters of sea water.Described originally as a sinkhole, then as a cryptovolcanic structure, it was finally recognized as a site of meteorite impact when shatter cones found in the structure confirmed its origin. When formed, the crater was most likely around 100 to 120 meters deep relative to the surrounding surface and “Since the rim was completely removed by erosion and yet the pit was not filled with air-borne sediments, the explosion is dated as shortly before the deposition of the Chattanooga shale, or in late Devonian time.” (Baldwin, 1963: 89).

Total intensity magnetic anomalies in the Flynn Creek area (after Roddy, 1964: 176). The Flynn Creek Structure is shown by the dashed outline.

In a subsequent, postimpact phase, Upper Devonian Chattanooga Shale was deposited in the crater and across the area on what was then a shallow marine shelf. In a post-impact phase of erosion, the ejecta blanket, terraced crater rim, crater-moat breccias, and central uplift were subjected to intensive erosion (either prior to or during transgression of the Chattanooga sea). This episode of erosion was followed by local transgression of the Kaskaskia sea, which inundated the erosional unconformity or peneplain.  After Chattanooga Shale was deposited over the area including the crater, several hundreds of meters of other types of sediments were deposited in the area. Regional uplift along the Nashville Dome has promoted erosion in the Flynn Creek area and thus generated an extensive valley network that cuts into, and thus helps expose, the terraced rim, breccia fill, and central peak.

The Flynn Creek Historical Marker.
This is a close as we could get to the point of impact in our van. We took this image from the east rim of the structure looking into the crater.

REFERENCES

THE FLYNN CREEK METEORITE IMPACT SITE AND CHANGING VIEWS ON IMPACT CRATERING
J.R.H. Ford,  Huay Kaew, Wayne Orchiston, and Ron Clendening Journal of Astronomical History and Heritage,  (2013).

MARINE RESURGE SEQUENCES IN DRILL CORES FC67-3 and FC77-3 — FLYNN CREEK IMPACT STRUCTURE, TENNESSEE USA. L. de Marchi, D.T. King Jr., J. Ormö, L.W. Petruny, D.R. Adrian, J.J. Hagerty, T.A. Gaither, and S.J. Jaret, Lunar and Planetary Science XLVIII (2017)