Rock Elm Disturbance

North American Middle Ordovician impact craters, which may be part of the Ordovician meteor event. Key: 1: Ames crater, 2: Decorah crater, 3: Rock Elm Disturbance, 4: Slate Islands crater.

The Rock Elm Disturbance is an impact crater in Wisconsin, United States, roughly 40 kilometers southwest of Menomonie.^[1] The disturbance is named for Rock Elm, Wisconsin, a nearby community.

Features

The meteorite is estimated to have been 170 m (560 ft) in diameter with a mass of 9×10⁹ kg (2.0×10¹⁰ lb) and impact velocity of 30 km/s (67,000 mph). The crater is 6 km (3.7 mi) in diameter, and fossils found in the rock filling the crater suggest it dates to the middle Ordovician Period, about 455 to 430 million years ago.^[2] It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of a proposed Ordovician meteor event that includes the Decorah crater in Iowa, the Slate Islands crater in Lake Superior, and the Ames crater in Oklahoma.^[3]

Composition

Researchers discovered a rare mineral called reidite at the Rock Elm impact site. Reidite is a dense form of zircon (ZrSiO₄),^[4] and has been found in three other massive meteorite impacts.^[4]

References

1. "Rock Elm". Earth Impact Database. University of New Brunswick. Retrieved 2009-08-19.
2. Peters, Christopher William, Middleton, Michael D., & Cordua, William S. (2002). "Paleontology of the Rock Elm Disturbance". Abstracts with Programs - Geological Society of America 34 (2): 95.
3. Vastag, Brian (18 February 2013). "Crater found in Iowa points to asteroid break-up 470 million years ago". Washington Post. Retrieved 19 February 2013.
4. Oskin, Becky (November 3, 2014). "Rare Mineral Discovered in Ancient Meteorite Impact Crater". Live Science. Retrieved 2015-02-17.

External links

• Article from Geotimes.com, March 2004
• Press release from the University of Wisconsin-River Falls
• Craters in Wisconsin

Coordinates: 44°43′N 92°14′W / 44.717°N 92.233°W