Another article about the Ilionois State Geologic Survey findings retrieved from the clutches of Google’s having identified McHenry County Blog in the latter part of 2006.
As I reported earlier, Brandon Curry of the Illinois State Geological Survey was in Crystal Lake last May conducting a bathymetric study to map the bottom of the lake.
But he was here in the middle of winter, too, a couple of years earlier.
Separate from the investigation of modern-day lake conditions, such as lake bathymetry (mapping the contours of Crystal Lake), is the study by Curry and other scientists of teeny-tiny fossils, such as ostracodes and plant pollen, to help understand past changes in lake levels and climate.
A sediment core he took in 2002 while the lake was covered by ice now shows scientists that Crystal Lake is 16,000 years old.
The core was taken in 42 feet water near the middle of the lake.
“At the bottom of our 30-foot long sediment core (going down to 72 feet below the water’s surface) were fossils of ancient spruce trees–needles and wood–that we had radiocarbon dated. We now know the age of the lake is about 16,000 years,” Curry told me. “That’s when the glacier left.”
From left to right can be seen a white spruce needle, snowbank willow leaf, and arctic bilberry leaf that Curry emailed me.
“You need about 5 to 10 of these for a radiocarbon date.”
He mentions a bronze box around the fossils, which I could not pick off my screen, “is 1 square centimeter.”
Curry also sent me a picture of the non-vegetable micro-fossil below, along with this explanation:
Here is…one of the microcritters found in the Crystal Lake core.
The species, Limnocythere varia, is an ostracode, a micro- crustacean.
The shell covers the organism like a clam shell clothes a clam (in other words, the ostracodes are bivalved), but the critter inside is built like a shrimp, and not a snail.
Ostracodes have been on this earth for a few hundreds of millions of years; this particular shell is about 8,200 years old, and is a clue that lake levels at that time were quite low.
This organism is quite abundant on the slopes of Crystal Lake at water depths between about 12 to 20 feet.
