WELLS CREEK IMPACT STRUCTURE

WELLS CREEK IMPACT STRUCTURE

by: Charles O’Dale

  • Type: Complex
  • Age ma: 200 ± 100 a
  • Diameter: ~12 km
  • Location: N 36° 23 W 87° 40
  • Shock Metamorphism: shatter cones & brecciation

a Dating Method: Geological – [see text]

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).

Wells Creek, Tennessee, USA (Laney et al 1978)
West of Cumberland City, the Wells Creek Structure is a syntypical cryptovolcanic explosion in the US. The 275 metre-wide, 20 million ton asteroid slammed into the earth at 40 km per second around 200 ± 100 Mya. A cross sections of the entire ~12 km complex crater shows the ripple of mangled Cambrian & Ordovician dolomite bedrock rising in the central uplift descending down to alluvial deposits, and then up on through Ordovician, Silurian, Devonian and Mississippian seabeds. Courtesy of USGS mapView.
Map showing the major structural features of Wells Creek (after Wilson and Stearns, 1968: 55).

Wells Creek is a confirmed meteorite impact site in Tennessee, USA. The Wells Creek structure was first noticed by railroad surveyors around 1855 and brought to the attention of J.M. Safford, Tennessee‟s State Geologist. He included an insert in the 1869 Geologic Map of Tennessee, which is the first known map to include the structure. The origin of the Wells Creek structure was controversial, and was interpreted as being either the result of volcanic steam explosion or meteorite impact. It was only in the 1960s that Wilson and Stearns were able to state that the impact hypothesis was preferred. Evidence for a Wells Creek meteorite impact includes drill core results, extreme brecciation and shatter cones, while a local lack of volcanic material is telling.

Since 325 Ma Mississippian rock is deformed at Wells Creek, the structure must have been formed after these rocks were deposited, and because the Cretaceous Tuscaloosa Formation (which dates to 75 Ma) has been found in the deformed area, the Wells Creek event must have occurred prior to the deposition of this Formation. No rock from any periods between these units have been found in any part of the structure, so on the basis of this geological evidence the age of the Wells Creek structure can only be estimated at 200 ± 100 million years.

Wells Creek shatter cones in snow (photograph by Andrew Tischler).

Shatter cones found in a 610-m core drilled near the center of the Wells Creek structure were concentrated at a depth of 30 meters. A few shatter cones were found below 60 meters being not complete or well defined, except for a single exception at 377 meters depth.

The Cumberland Fossil Plant situation on the north section of the Wells Creek structure. The north rim is illustrated in the extreme left of the image with the east “crater rim” visible in the far background.

REFERENCE:

J.R.H. Ford, Wayne Orchiston, Ron Clendening; THE WELLS CREEK METEORITE IMPACT SITE AND CHANGING VIEWS ON IMPACT CRATERING Journal of Astronomical History and Heritage, 15(3), 159-178 (2012).