Well, I'm back from Chicago, and my fossil hunting expedition! My abilities to find fossils on this trip can be summarized by one word: FAIL!!!
This was a field trip sponsored by the Field Museum of Chicago, a place I spent much time at in my youth. For at least 20 years, they've sponsored fossil hunts in the Mazon Creek area. My dad and I participated in one some twenty years ago, as mentioned in this post; in recent months, I suddenly got the urge to go back and try my luck again.
The fossils at Mazon Creek are some 300 million years old. They appear in flat, roundish rocks known as concretions. In short, the original biological material was encased in mud underwater. The decay process creates a chemical reaction around the material, creating ironstone, which protects the fossilizing specimen from being destroyed.
The Mazon Creek area itself was formerly a heavy mining area, and fossil hunts now center around mining 'spoil piles', the piles of rubble that miners excavated in order to get at the good stuff. These piles are constantly being eroded by the weather, exposing new fossils for prospective hunters.
Once a concretion is found, it can be split open with a hammer, hopefully exposing a well-preserved fossil within. A fossil hunt at Mazon Creek consists of a scramble over steep slopes of loose rock and soil, searching for tan-colored concretions to crack open.
Unfortunately, most concretions do not contain well-preserved fossils. The concretion process might have been started by an extremely small piece of vegetable matter which has left no visible trace. Or, even if a significant specimen is subject to concretion, it may have decayed before it could fossilize, leaving a tantalizing but unrecognizable impression in the stone. Two hand-found examples of this latter process are shown below, the 'blob fossil' and the 'stick fossil':
This was about as successful as my dad and I got, with the exception of the crown jewel of our hunt, a plant stem:
The identification was made by our guide, a very nice and helpful paleontology graduate student.
The terrain is frighteningly difficult to negotiate, at least at the 'pit' where we were hunting. Thick, pointy undergrowth blocks passage to the spoil piles, as illustrated in the picture below:
Once at the spoil pile, one has to cling precariously on the steep, loosely-packed slope, sifting through rocks and dirt and avoiding weeds, spiders and a fall into the lake. As my Dad pointed out, it's quite amazing that they didn't make us all sign safety waivers on the way out there!
Although we didn't come home with spectacular specimens, we had a fun time. Below is a pic of Dad and I after 3 hours of trudging through undergrowth, clinging to cliff sides and digging in 90-degree heat:
Though I suppose we should really have a caption for this picture:
To our credit, my Dad and I were at least trailblazers on the trip! We pushed forward into weeds, with the most of the tour group following us. I had a good time feeling like a daring explorer, and am still itching all over from the various scratches and insect bites I suffered.
Apparently, though, it takes more than a single afternoon to develop good paleontology skills! Who would have thought? 🙂