No. 105: May-Jun 1996
The recent impact upon Jupiter of a procession of chunks from Comet Shoemaker-Levy 9 has encouraged geologists to look for crater chains here on earth. Such have been spotted on the moon, and it is unlikely the earth escaped such bar rages. Of course, older terrestrial craters are harder to identify due to the ceaseless geological activity here on earth.
In the first 1996 number of Geophysical Research Letters, M.R. Rampino and T. Volk describe a possible swath of meteoric devastation across the North American Midwest.
"Eight circular geologic structures ranging from about 3 to 17 km in diameter, showing evidence of outwarddirected deformation and intensive brecciation, lie within a linear swath stretching about 700 km across the United States from southern Illinois through Missouri to eastern Kansas. Based on their similar geological characteristics and the presence of diagnostic and/or probable evidence of shock, these structures, once classified as 'crypto volcanic' or 'cryptoexplosion' structures, are more confidently ascribed to hypervelocity impact. No other similar occurrence of aligned features is known, and we calculate the probability of a chance alignment to be less than 10- 9 ."
The craters are all roughly the same age: 310-330 million years. Rampino and Volk suspect they were formed all at once by a string of asteroids or comets.
(Rampino, Michael R., and Volk, Tyler; "Multiple Impact Event in the Paleozoic: Collision with a String of Comets or Asteroids?" Geophysical Research Letters, 23:49, 1996)
Comment. We cataloged a possible chain of meteorite scars in Argentina, near Rio Cuarto, in SF#80.
|Linear chain of known and probable impact structures across the North American Midwest.|