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Revisiting the Maquoketa in Northern IL


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Today I decided to revisit a stream exposure of the Upper Ordovician Maquoketa Group in northern IL. I believe these outcrops are all Brainard Shale, which is the second highest member of the Maquoketa in Northern Illinois. The olive-gray shales exposed at the base of the outcrops are packed with Tentaculites, and the few times I've been here I've always searched for those. Today I wanted to explore more of the creek and see what else I could find.

 

The stream was running pretty fast but wasn't too high, despite all the recent rain.

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Shale and dolomite outcrop for quite a distance along the stream, although the water is usually too high to get to many of them.

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I probably won't come back until the water level drops quite a bit so I can wade through, the stream isn't super deep.

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The stream runs near shops and well-traveled footpaths, so to be respectful I don't hammer here. That makes it a little tough since most rock faces are highly weathered and covered with vegetation, but some nice things can still be found. Water-worn brachiopods are common sights, though rarely worth collecting.

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Tentaculites are fairly common along most of the stream. Often they are fairly worn out, like this one below.

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But if you look in recently fallen shale pieces you can find some nice ones. I took this one home.

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This one was in a large rock and I didn't bother trying to extract it, but it's a good example of how large they can get here.

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Isotelus fragments are very common. I've found a genal spine and hypostome on past trips, but nothing more complete.

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Another worn brachiopod.

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There are also tons of modern critters. A lot of weird looking bugs that I do not particularly enjoy, but I did see this cute fella today.

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Last time I was here I came across this very large rock face about 20 yards from the stream's edge.

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There is a lot of shale to pick through, but there a lot of it seems to be fairly unfossiliferous.

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That said, last time I was here I took home a chunk of shale just for kicks and split it open, and found some quite nice brachiopods. The layer they came from is about 2 meters off the ground and can be identified by the plentiful but highly weathered brachiopods on the surface.

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I took home a few chunks from this layer to split tomorrow, so we will see if this trip proved fruitful. Regardless, it was nice to get away from home for a bit and poke around.

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Tidgy's Dad

Very nice report with great pictures.:)

Love the Tentaculites. 

Thanks for sharing. 

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deutscheben

Thanks for the report, that snail is adorable!

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I, too, love the Tentaculites :wub:

Beautiful scenery, too!

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Nice scenery indeed, typically paleozoic. Not Jurassic clay, sucking you under:D

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