Excavation for subdivision puts geologists in a hole
Oh yeah, it's a hoot when a demolition or a renovation job uncovers a time capsule somebody stuck in the cornerstone of a building a century or so ago. Those vintage newspapers, fading pictures, antique coins and the like inside are interesting. Things sure have changed.
But nothing like the changes you see when you open a 20,000-year-old time capsule.
If newspapers had been around to cover it, the big story might have been the recession – not in the economy but of the thick sheet of glacial ice that covered the area along west Kirby Avenue and much of the rest of Illinois to the north.
Pictures, had there been cameras and photographers, might have shown a tundra landscape being uncovered, one with chilly temperatures – even in July – which actually doesn't sound half bad right now.
No coins to seal in this ancient time capsule, but plenty of snail and clam shells, the odd skeleton of a small fish, spruce needles and leaves from arctic blueberry plants and dryas, a low bush more likely to be seen today in far northern Canada than East Central Illinois.
"It was cold," Bill Shilts, chief of the Illinois State Geological Survey said recently, standing in a big hole off Kirby west of Staley Road. "(Dryas is) a very distinct tundra plant that grows outside the tree line in cold conditions," he said.
The hole, a drainage basin in connection with the ongoing development in the area, opened a geological time capsule on an era when East Central Illinois was a hospitable place for dryas and other arctic flora and fauna.
"It's just like we've got a snapshot in time," Shilts said. "This was very unexpected. Nobody has ever looked at exposures like this in Champaign County."
But Shilts happens to be moving into a new home across the street from the soon-to-be lake, and he's a fellow who knows glacial geology – it's his specialty as a geologist – when he sees it. The Ohio native spent 25 years working for the Geological Survey of Canada, often in the arctic, before becoming chief of the Illinois survey in 1995.
When excavators for Hallbeck Homes dug the hole, Shilts couldn't resist having a look at the geology. Once he got a look, he knew the geological survey needed to document the find before it ended up under water. A survey team, with developer Rick Hallbeck's OK, got a closer look this month.
What appeared to be racing stripes running along the walls of the hole were actually the remnants of glacier-fed streams, small "kettle" lakes and bogs that once characterized the area, along with the fossilized remains of plant and animal life.
The locale probably resembled the west side of Hudson Bay in far northern Canada, above the tree line, or northern Alaska, said Shilts and Brandon Curry, one of the survey geologists examining the find. The geology and fossils are consistent with a cold, windy environment.
As the glaciers retreated, the streams and lakes dried up and the area was encased in a buildup of swirling dust, eventually to be covered by prairie, a time capsule waiting to be discovered.
Curry said the find is the farthest south that fossil dryas and arctic blueberry have been recorded in the Northern Hemisphere.
The plant fossils allowed the state survey to date the find, by measuring the radioactive decay of carbon found in formerly living things like plants and animals to determine how long ago they lived.
Deposits like this aren't often uncovered, Shilts said, because they represent what passes for lowlands around here.
It might not look like it from our perspective, but viewed from the air the local landscape is actually ribboned with low ridges, where the glaciers piled up crushed rock materials in hillocks called moraines. Development locally has tended to take place on those ersatz highlands.
The hole represented a rare opportunity to study the geology left behind in glacial flats, to look at the state's environmental past, and to expand knowledge of what lies beneath our feet in Illinois.
The distribution and character of such deposits are difficult to document and map absent excavation, but they're important to developers and to public officials making decisions in areas undergoing development, said Steve Brown, another survey geologist studying the find.
The subsurface information, matched with surface features, also can make it easier for geologists to predict what might lie beneath similar locations, Brown and Curry said.