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Science Frontiers ONLINE No. 121: Jan-Feb 1999 |
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An Arkansas Tsunami Deposit?
Yes, Arkansas is hundreds of kilometers from any ocean. Could a tsunami ever reach Little Rock, or even 120 kilometers northeast of Little Rock where, atop a 76-meter (250-foot) hill are perched giant blocks of sandstone. These blocks range up to 7.6 meters (25 feet) in size and weigh many tons. No native rocks in the area match them. The Ice Age glaciers never reached Arkansas, so they can't be glacial erratics. Where did they come from? One clue is the presence of glauconite in the sandstone. Glauconite is common in marine rocks, so suspicion points toward the Gulf of Mexico.
Geologist G. Patterson, University of Memphis, thinks that the huge chunks of sandstone came from coastal Louisiana and were carried some 650 kilometers (400 miles) inland by the giant tsunami raised by the asteroid or comet that smashed into the Yucatan to close out the Cretaceous. That, of course, was when the dinosaurs were forced into oblivion. But could the tsunami really have transported such huge rocks 650 kilometers?
(Falk, Dan; "Washed Up," New Scientist, p. 26, November 7, 1998.)
Comments. Tsunami debris from the end-Cretaceous impact has been found along the Gulf Coast and on some Caribbean islands. In northeastern Mexico, geologists have found a debris layer 3-meters thick that is also of the right age. This layer contains tektites, glass spheres, plant material, and an iridium anomaly. (SF#85) However, these debris deposits can hardly compare to the far-inland Arkansas sandstone chunks.