Sedimentary Rock Limestone

Associated Smithsonian Expert: Catherine (Cari) Corrigan, Ph.D.

Cari Corrigan with two meteorites from the collection.

Photographed by Brittany M. Hance, Smithsonian Institution.

Dr. Cari Corrigan is a research geologist at the Smithsonian National Museum of Natural History who specializes in the study of rocks called meteorites that come from other planetary bodies in our solar system. While growing up in western Michigan, she often went hiking and exploring in the woods and lakes near her house. During her first two years in college, she took an astronomy class and a geology class, and wondered how she could combine the two. This led to her discovery of the field of planetary sciences, which she decided to try to to make her career. After earning her PhD from Case Western Reserve University studying Martian meteorites in 2004, she worked as a postdoctoral fellow at both the Smithsonian and at Johns Hopkins University Applied Physics Lab, and joined the Smithsonian permanently in 2008. In both 2001 and 2004, Corrigan participated in the Antarctic Search for Meteorites Program as a field member. These teams travel to Antarctica annually to collect meteorites from the Antarctic ice, where they have fallen and remained frozen since they fell to Earth. The program has returned over 20,000 meteorites for research and educational purposes since it began in 1976. At the Smithsonian, Corrigan curates this collection of Antarctic Meteorites, while also conducting research on both Antarctic and non-Antarctic meteorites from the Moon, Mars, and the asteroid belt.

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This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.
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Artist interpretation of a meteorite impact, creating an impact crater, shocked quartz, breccia, and shattercones.
Image created by Karen Carr Studio, Inc., used with permission

About Kentland Quarry

Deep underneath the soil of Indiana lies some of the hardest rock around. Limestone was deposited as sediment at the bottom of an ancient ocean some 400 million years ago. Since then the ocean has disappeared, and the sediments turned into rock, and have been buried under hundreds of feet of more recent sediment. About 100 million years ago a large meteorite struck what is now northwest Indiana, creating an impact crater about 12 kilometers, or 7.25 miles, across - the fourth largest in the United States. The impact was large enough that the central area of the crater rebounded back upward. This created high ground that was not buried as deeply by the sediments that covered the rest of the crater and the Midwest.

Artist interpretation of a meteorite impact, creating an impact crater, shocked quartz, breccia, and shattercones.
Image created by Karen Carr Studio, Inc., used with permission

About Shatter Cones

Shatter cones are very reliable evidence of a meteorite impact. They are identified by the distinctive-looking, conical shaped features that show striated fractures on their surfaces. They can form in any type of rock, though most well-formed shatter cones form in fine-grained rocks and can measure from millimeters to meters in length. Shatter cones form under relatively high pressure, greater than nuclear bombs, and are usually found below a crater's floor and in the central uplift feature of complex impact craters.

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Kentland limestone is used as railroad ballast throughout the state of Indiana.
Photographed by Susan Daniel, Rogers Group, use with permission

How People Build from Kentland Quarry

The large impact at Kentland caused two benefits that allow humans to use the limestone there today. First, the impact was large enough that there was a rebound effect, where the central area of the impact came back up several hundred feet. Since the rock is near the surface people can access it easily without needing to remove much soil above. Secondly, the impact fractured the rock making it much easier to remove from the ground. Today, limestone from the Kentland Quarry is used for concrete in bridges and buildings, asphalt, rail ballast, and laying the foundation for roads to local windmill farms.

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