This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

13 April 2008

New Article in Geology on Chesapeake Bay Impact (1 - 1.5 miles in diameter, about 35 million years ago)

Selections from the article...

A Western Michigan University graduate student is the lead author of an article in the April issue of Geology magazine that explores how the crust of the Earth behaves after being hit by a comet or asteroid and could shed light on how the moon's surface was formed.

Travis Hayden, a graduate student in geosciences from Portage, Mich., is among seven authors who contributed to the article, titled "Impact effects and regional tectonic insights: Backstripping the Chesapeake Bay impact structure." Hayden's main advisor, Dr. Michelle Kominz, a WMU professor of geosciences, also contributed to the article.

Published by the Geological Society of America, Geology is one of the most popular and widely read earth science journals in print, with 20 or more thought-provoking articles each month. The article written by Hayden, Kominz and five other scientists examined the impact of an object, probably a comet or asteroid, that struck the Earth in the Chesapeake Bay area. The object was 1 to 1.5 miles in diameter and hit the Earth about 35 million years ago, Hayden says.

It was widely thought that such an impact would have long-lasting effects on the Earth's crust. In addition to forming a very large crater, scientists believed a significant amount of heat would have been generated in such a strike, melting a portion of the Earth's crust.

"The interesting thing was that we found it behaved exactly the opposite of what everybody expected," Hayden says. "Everyone had assumed that the impact released a whole bunch of heat, melted a lot of rocks and this heat actually changed how the crust behaves over time." Hayden says the impact did generate a lot of heat and melted a lot of rock, but most of the molten debris was thrown out of the crater. All the material that then filled in the crater afterward wasn't hot at all--it was cold.

And that affected what happened to the crust, Hayden says. Scientists had believed an impact and resulting melting of rock in the crater would have resulted in uplift within the crater followed by subsidence. Their results showed just the opposite happened. The crust subsided about 100 meters, and that was followed by uplift. "This was out of left field," Hayden says.

The results help to better understand how such impacts affect the crusts of the Earth and other bodies, including the moon, Hayden says.

"The seas of the moon, such as the Sea of Tranquility, are thought to be formed by this kind of melt, when a big impact came in, melted a whole lot of rock and then kind of paved everything out pretty smoothly" Hayden says. "But no one had been able to test it. So this was the first time we've ever been able to look at it in the real world to see if it actually happens. We found that for smaller impacts like the one that occurred at Chesapeake Bay, it didn't. This doesn't rule out larger impacts producing this effect."

"Grad student is lead author of article in Geology"
08 April 2008

Link: Western Michigan Article


"Impact effects and regional tectonic insights: Backstripping the Chesapeake Bay impact structure"
Article: pp. 327–330
Volume 36, Issue 4 (April 2008)

Travis Hayden1,*, Michelle Kominz1, David S. Powars2, Lucy E. Edwards2, Kenneth G. Miller3, James V. Browning3, and Andrew A. Kulpecz3

1 Department of Geosciences, Western Michigan University, 1187 Rood Hall, 1903 W. Michigan Avenue, Kalamazoo, Michigan 49008, USA
2 United States Geological Survey, National Center, Reston, Virginia 20192, USA
3 Department of Geosciences, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA

Abstract: The Chesapeake Bay impact structure is a ca. 35.4 Ma crater located on the eastern seaboard of North America. Deposition returned to normal shortly after impact, resulting in a unique record of both impact-related and subsequent passive margin sedimentation. We use backstripping to show that the impact strongly affected sedimentation for 7 m.y. through impact-derived crustalscale tectonics, dominated by the effects of sediment compaction and the introduction and subsequent removal of a negative thermal anomaly instead of the expected positive thermal anomaly. After this, the area was dominated by passive margin thermal subsidence overprinted by periods of regional-scale vertical tectonic events, on the order of tens of meters. Loading due to prograding sediment bodies may have generated these events.

Link: Geology Journal Reference

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