38th parallel structures
The 38th parallel structures, also known as the 38th parallel lineament, are a series of circular depressions or deformations stretching 700 km (435 mi) across southern Illinois and Missouri into eastern Kansas at a latitude of roughly 38 degrees north.
Rampino and Volk (1996) postulated that these structures could be the remains of a serial meteorite strike in the late Mississippian or early Pennsylvanian periods. Difficulty in determining the age of many of the structures and doubts about the exogenic origins of several of them leave some geologists skeptical of this hypothesis. As of May 2009, only two of the structures, Decaturville and Crooked Creek, are listed as confirmed in the Earth Impact Database.
There is evidence that at least some of them, such as Hicks Dome, are volcanic in origin. They are associated with faults and fractured rock, and are accompanied by igneous rocks and mineral deposits. Hicks Dome is a structural dome which has its central Devonian core displaced upward some 4,000 feet in relation to the surrounding strata. The dome has small associated igneous dikes around its flanks.
Interest in the possibility of serial impacts on Earth was piqued by observations of comet Shoemaker–Levy 9 impacting on Jupiter in 1994. It is estimated, however, that the likelihood of such an event on Earth is vanishingly small because the Earth's weaker gravitational field is much less able than Jupiter's to pull a speeding object close enough to be torn apart by tidal forces. However, evidence of serial impacts on the Moon can be seen in several chains of craters.
- Gillman, Joe (ed.), Association of Missouri Geologists Field Trip Guidebook, 51st Annual Meeting, Rolla, Missouri, October 1–2, 2004, 2004, Missouri Department of Natural Resources, Geological Survey and Resource Assessment Division, p. 15
- John Spray (director) (2009-05-20). "North America". Earth Impact Database. Planetary and Space Science Centre, University of New Brunswick. Retrieved 2009-09-27.
- Raymond Wiggers, 1997, Geology underfoot in Illinois, Mountain Press, p. 252-256 ISBN 0-87842-346-X
- Rampino, M.R, and Volk, T. 1996. Multiple impact event in the Paleozoic: Collision with a string of comets or asteroids?. Geophys. Res. Lett. 23, 49-52. (Abstract)
- Evans, Kevin R.; Mickus, Kevin L.; & Rovey, Charles W. III (2003). The Weaubleau Structure: Evidence of a Mississippian Meteorite Impact in Southwestern Missouri. Association of Missouri Geologists Field Trip Guidebook, 50th Annual Meeting. Missouri Department of Natural Resources. PDF
- Luczaj, J. 1998. Argument supporting explosive igneous activity for the origin of "cryptoexplosion" structures in the midcontinent, United States. Geology 26(April):295.