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Under the Seamans Center

Posted on April 20th, 2016

Fossils provide a glimpse of life in Iowa 385 million years ago

Fossiliferous limestone from about 30 feet below the surface at the Seamans Center expansion building site.

Fossiliferous limestone from about 30 feet below the surface at the Seamans Center expansion building site.

Most of us rarely think about what might be 25 feet underneath our feet. If you dug down that far, you might find remnants of a past very different from the world we live in today.

That’s what happened recently at the Seamans Center expansion site on the University of Iowa campus. As Knutson Construction workers drilled into the bedrock 25–35 feet beneath the surface to get a solid footing for the caissons that will hold up the new building, they began bringing up some unusual looking rocks. Fascinated, foreman Dave Mellecker set them aside.

Later, he showed the rocks to others, including geologist Ryan Clark of the Iowa Geological Survey (a unit of IIHR—Hydroscience & Engineering). Clark says that the chunks of limestone from the building site do include fossils, and here’s the kicker: They’re about 385 million years old.

“They were probably covered up during the last glaciation,” Clark says, “so they haven’t seen the light of day in at least half a million years or so.” He says the fossilized creatures were very akin to a modern coral reef—corals, sponge-type animals, and some smaller animals such as brachiopods (a type of bivalve) and crinoids (a relative of the starfish).

Rocks like this one caught the eye of construction workers at the Seamans Center expansion site.

Rocks like this one caught the eye of construction workers at the Seamans Center expansion site.

Geologists have known for a long time that Iowa has been covered by oceans many times in its geologic history, and these fossils confirm this well-understood fact. “The fossils themselves—we know a lot about them, we knew they were there,” Clark says. “So in that regard, it’s not terribly unique.” What’s interesting to Clark and others, though, is the unique look of the fossils. Rock outcrops around the University of Iowa campus reveal similar fossils, but these stand out in relief in a way that is unusual, Clark explains. “You don’t see that in a normal exposure.”

He says that slightly-acidic rainwater percolating down through the soil eats away at the softer material, leaving behind the exposed fossils, which are solid calcite and thus much more durable. “As what we call matrix material has been leached away, it has exposed these fossils in a really nice form,” Clark says.

IGS Geologist Ryan Clark speaks on camera for the media.

IGS Geologist Ryan Clark speaks on camera for the media.

The Seamans Center fossils have garnered a lot of media attention, and Clark has been interviewed by journalists from the Cedar Rapids Gazette, Fox 28, KCRG-TV, and KWWL-TV. The story took off and appeared in cities far from Iowa and the Midwest, including Salt Lake City, Tampa, Miami, Orlando, Green Bay, West Palm Beach, and Memphis. “I couldn’t believe it!” Clark says. “I think the thing that really captivated people is the idea of 385 million years. I think in those time frames all the time, but it’s not what most people do.”

If you’re on the University of Iowa campus and want to see similar fossils, all you have to do is stop by the Old Capitol, which was built from the same kind of rock quarried from sites around campus (an outcrop is visible across Riverside Drive from the Stanley Hydraulic Lab). The lower sections of the Old Capitol are made from “fossiliferous limestone,” Clark says. Get up close and you can see big coral fossils and the like.

Some of the Seamans Center fossils will be on display in Trowbridge Hall on the UI campus, which is home to the Iowa Geological Survey. “It’s partly a museum,” Clark says. “We love showing them off, and they’re really interesting. You can learn a lot from them.”

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