July 11, 2015

7/7/15 - Devonian Fossil Gorge

Devonian Fossil Gorge Entrance Plaza
We were staying at the Corps of Engineers Campground at Coralville Lake near Iowa City, Iowa. Near the campground was the entrance to the Devonian Fossil Gorge. Fossils? In Iowa? Although George wasn't interested (probably because he was worn out from going to Amana), I had to go check it out. I grabbed my camera and walked to the other end of the campground.

There are displays in the Entrance Plaza about the fossil bed. In 1993 heavy rains filled the reservoir. Water spilled over the spillway (I guess that's what spillways are for) for at month at 17,000 cubic feet per second. It washed out the road and the campground (no campers were damaged during the making of the gorge) and scoured the soil and sand down to bedrock and beyond. As the waters receded, there was clear evidence of the lake bed and the plants and animals that existed here during the Devonian Period. In 2008, there was another flood (and I thought it rained a lot in Seattle!) which washed away the huge boulders left from the first flood.
North end of fossil bed towards dam spillway
I skimmed over some of the plaques on the walls at the Entrance Plaza, picked up my brochure and headed down into the gorge. There are some big polished boulders along the ramp with examples of some of the fossils found in the gorge. Even people with no prior fossil experience can enjoy looking for them where they're in such plenitude, falling all over each other for space in the rock.
The brochure features a map with numbers. The numbers correspond to hexagonal plaques fastened on the ground near a "Discovery Point". The Key in the brochure explains what we're looking at--or for, in some cases.
It was like a grown-up scavenger hunt!
I found these in the ledge around the gorge.

Sometimes I'd find the number, and couldn't find the fossil it was describing. Descriptions in the Key were definitely ambiguous scavenger hunt clues. Phrases like "6 feet north", "near this point", "around this area" made the search even more like looking for treasure. These are a kind of colonial coral called Hexagonaria.
#4 - These things that look like nails are actually Crinoid Fossils. They're related to starfish. (How do they even postulate that a piece of what is now rock is related to something as squishy as a starfish?)
In some places there are so many fossils I couldn't figure out which ones the Key is referring to. That goes back to not paying enough attention to the descriptions of the fossil types up by the displays. I think these might be brachiopods.
#7 - Thin fractures in the bedrock are sometimes filled with white calcite crystals.
#10 - This area was formed by ground water dissolving prt of a limestone bed. It's called karstification.
#19 - The Key describes these as chert nodules, but when I zoom on them, they look more like the coral stuff from above. I must have missed the chert nodules. Oh, well, the brochure says they're not where they're supposed to be anyway.
I found all the plaques except number 17--which BTW was described as "Abundant Fossils". I really wanted to see that one. Didn't even look for 18--it was across the road back by the beginning and I decided to skip it. This was more interesting anyway.
More pictures from the fossil beds:  Devonian Fossil Gorge

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