Francis Creek Shale

[connorp]

The Francis Creek Shale in northeast Illinois is best known for producing Mazon Creek concretions. However, the shale itself also contains an extremely diverse and well preserved flora (and fauna occasionally). Unfortunately, the shale is extremely soft, and quickly weathers to clumps of clay. This makes collecting from the shale very challenging, and most collectors don't even bother trying. On a recent trip I found some fresh chunks of shale and decided to try and save some of the plants. Even working with fresh shale, it was still very hard to extract anything. Larger pieces crumbled easily, flat surfaces flaked as they dried, and some fossils were destroyed just by accidentally brushing a finger against them. These specimens represent what I was able to save. They have been sitting out for over a week now and seem stable as long as they are not handled, but only time will tell if they last.

 

Crenulopteris acadica

 

Crenulopteris subcrenulata

 

Neuropteris fimbriata (seed fern pinnule)

 

Lepidostrobophyllum lanceolatus (cone bracts)

 

 

On the left is a fern I am unsure of, any thoughts are appreciated.

On the right is Stigmarioides. I have not found many examples of this taxa in concretions but it seems fairly common in the shale.

 

I think this is also Stigmarioides. Many of the scars are plugged with pyrite - it was bright gold when I first split the shale but oxidation has darkened it.

 

Hopefully these will last, but if not I wanted to post photographs in case they don't.

 

 

Edited July 11, 2022 by connorp

[Ludwigia]

I would suggest spraying them with artists fixative.

[digit]

I would normally suggest consolidating with B-72 dissolved in acetone or ethanol but I'm afraid this might end up softening the clay/shale more than you want. Roger's idea of an artistic fixative (used to protect pencil, pastel, chalk, or charcoal drawings) would probably work the best. You should be able to pick up a spray can of fixative at your local art/craft store (there are a couple of national chains) or simply look for a clear mat spray paint at any of the big home improvement stores.

 

 

Cheers.

 

-Ken

[Nimravis]

Nice finds Connor and I feel your pain, I use to find some nice pieces. They were beautiful to look at and wonderful to hold, but they always broke, so I consider they sold. I always left them because they just turned to pieces in my bag as I collected. I was glad I could use that little saying that you see from time to time in little shops. Lol

[deutscheben]

Thanks for posting, it is nice to see this different aspect to a well-trodden area that might otherwise be overlooked. 

[Mark Kmiecik]

I collected a lot of fossils in the shale, and it will turn to powder eventually. If you want to keep them intact you need to consolidate them. I think Paraloid should work from my experience with FCS specimens. All of mine -- literally ALL of them -- self destructed over the course of twenty years of drying out getting moved and jostled. I ended up with a 20-lb box of dust instead of about 50 specimens.

[connorp]

1 hour ago, Mark Kmiecik said:

I collected a lot of fossils in the shale, and it will turn to powder eventually. If you want to keep them intact you need to consolidate them. I think Paraloid should work from my experience with FCS specimens. All of mine -- literally ALL of them -- self destructed over the course of twenty years of drying out getting moved and jostled. I ended up with a 20-lb box of dust instead of about 50 specimens.

Thanks for the info. I will try consolidation on a few this week. I'm not confident these would even survive the acetone soak, but we shall see.

[Mark Kmiecik]

1 hour ago, connorp said:

Thanks for the info. I will try consolidation on a few this week. I'm not confident these would even survive the acetone soak, but we shall see.

Acetone does not have anywhere near the amount of surface tension as water, so I think they should be fine. Of course, test a piece of matrix and a small section of an insignificant specimen before total immersion. 

[Tidgy's Dad]

Interesting thread. Nice finds too.

Thank you for sharing. 

[mr.cheese]

Interesting read! I have found a few ammonites in clay and managed to get away with air drying them but I don't envy you trying to stabilise shale! Let us know how you get on please.