Mazon Creek Concretions: The Good, the Bad and the Ugly.

[Nimravis]

I was watching the Clint Eastwood movie “The Good, the Bad and the Ugly” recently and it made me think about collecting Mazon Creek concretions and how the movie title applies to them.

 

Let’s start with a couple of the “Good” things:

 

-Over the years there has been numerous books and articles written about the Mazon Creek area and concretions and they provide outstanding information for the collector of all levels.

 

 

-With about 400 species of flora and about 320 species of fauna that are found in these ironstone concretions plus the remarkable preservation of so many soft bodied animals, I feel that it rivals the fossils found in the Burgess Shale and Solnhofen.   

 

 

 

 

 

[Nimravis]

If the concretion opens along the “plane line”, and it does contain a fossil, you get two fossils for the price of one, as with this Essexella asherae Jellyfish..

 

 

 

Fossils can be found in small concretions- such as this horseshoe crab.

 

 

Or in large concretions, like this one that contains a Neuropteris fern and a triple annularia.

 

 

And with this Lepidostrobophyllum majus.

 

 

 

 

[FossilDAWG]

   

Don

[Nimravis]

There are times when the concretions that you find and open contain fossils that are 3 dimensional, such as the below fossils of sub-surface bark.

 

 

 

 

Here are a couple of the “Bad” things:

 

Due to the amount of vegetation that covers a lot of the collecting areas, the weathering process of the strip / shaft mine spoil piles has prevented more concretions from being exposed, thus the number of concretions found are less than in years past. Below is a 2012 aerial shot of Pit 11’s “Tipple Hill”, this area has even less exposed areas now.

 

 

 

 

Not all concretions contain fossils and even if they open along the “plane line”, they might not have a fossil.

 

 

 

Even though it is believed that all concretions had to have some type of inclusion to form, many concretions that you may find are not worth picking up- through time, you will see what concretions are “Bad” and which ones are “Good”.

 

Here are a couple of concretions that I can almost guaranteed will not to contain a fossil.

 

 

 

[Nimravis]

Here are typical concretions that are found at Pit 11 (Essex Biota-Marine) and that I would collect, they have great shapes and are always on the smaller size, though larger ones are found.

 

 

Here are typical concretions that are found at Pit 4 (Braidwood Biota-Fresh) and that I would collect, they have various shapes and many are on the larger size.

 

 

When I say that the Pit 4 concretions are large, they are also heavy.

 

23 Pounds

 

 

15 Pounds

 

 

 

When I would collect at Pit 4 or at Pit 11, I would often do it on a bicycle and would put concretions into packs and hang them on my bike and strap them on my back – multiple packs get very heavy.

 

The opening of concretions is a real pain. The best way to do this is by the “freeze / thaw” method, in which you place the concretions in water and freeze / thaw them until the crack open along an invisible “plane line”. The only issue with this, is that it can take multiple rounds in the freezer or outside over the winter to open them. Even after doing this, the concretion may not open and I often revert to the old hammer method. The only problem with this, is that many times you can destroy a very nice fossil, as shown below.

 

 

Depending on the area that you are collecting concretions from is when the “Ugly” comes in. If you are lucky enough to have a concretion that has a fossil, many times these are not a pristine as they are from other spots and they need to be cleaned. I will usually try tap water and if that does not work, I will soak them in undiluted white vinegar for a couple minutes and lightly go over them with a toothbrush. Care needs to be given to this process since you do not want to damage the fossil.

 

Pecopteris Fern

 

 

An Annularia is under all that gunk.

 

 

The identification of some of your finds can also be a problem, especially when it comes poorly preserved or weathered opened concretions. Many times your mind and eyes play tricks on you and you see features that are only suggestive shapes or stains. Unfortunately, I do not have an example to show you since I dispose of them immediately.

 

If you ever have a chance and you are near the Braidwood, Illinois area, you need to make a quick stop to this world famous Lagerstatte for yourself and see what you can find.

[Miocene_Mason]

Those are some truly beautiful finds! Very informative, thanks for posting! Hope to get there someday.

[Nimravis]

6 minutes ago, WhodamanHD said:

Those are some truly beautiful finds! Very informative, thanks for posting! Hope to get there someday.

Thanks much- I think that you would like to check it out, it is the definition of Fossil Hunting, you really have to look around.

[Macrophyseter]

Never realized that there are so many unique variations of fossiliferous nodules 

Your tips on these nodules are very helpful, especially the types of nodules that most most likely to have fossils, and how to make a solid one create a visible plane line.

This will actually be something I'll have to look at over and over if I'll ever go to Mazon Creek. Thanks for posting this!

[smt126]

Do you have any before and after pictures of cleaning them? The ones I have I never know if I should leave them alone or try to scrub them up some.

[Nimravis]

2 hours ago, smt126 said:

Do you have any before and after pictures of cleaning them? The ones I have I never know if I should leave them alone or try to scrub them up some.

I will check to see what I have

[Wrangellian]

Nice presentation.

I guess you would have gotten a better split on that fern using the freeze-thaw instead of hammer, but could you not take a small chisel/hammer and knock those sticking pieces off and glue them onto the other side?

The only time I every had a go at splitting Mazon conc's, the freeze-thaw method only made the 'rinds' crumble away and leave a messy surface and reduced area. Of course I never found much worth mentioning in that batch, but I understand it can still be a problem with the fossil-bearing ones. What is your experience?

[Nimravis]

1 hour ago, Wrangellian said:

Nice presentation.

I guess you would have gotten a better split on that fern using the freeze-thaw instead of hammer, but could you not take a small chisel/hammer and knock those sticking pieces off and glue them onto the other side?

The only time I every had a go at splitting Mazon conc's, the freeze-thaw method only made the 'rinds' crumble away and leave a messy surface and reduced area. Of course I never found much worth mentioning in that batch, but I understand it can still be a problem with the fossil-bearing ones. What is your experience?

 In regards  to trying to use a chisel and get the rest that off, I would just damage the concretion more , since this one is very fragile. 

 

I do like the freeze thaw method, but I have so many concretions to go through from years of collecting , I do use a hammer and a lot of them. And in regards to your last comment, some concretions hold up better To a hammer than others.

[RJB]

Excellent post Nimravis.  Lots of info and some neato pictures. 

 

RB

[Nimravis]

12 minutes ago, RJB said:

Excellent post Nimravis.  Lots of info and some neato pictures. 

 

RB

Thanks RB

[Wrangellian]

8 hours ago, Nimravis said:

 In regards  to trying to use a chisel and get the rest that off, I would just damage the concretion more , since this one is very fragile. 

 

I do like the freeze thaw method, but I have so many concretions to go through from years of collecting , I do use a hammer and a lot of them. And in regards to your last comment, some concretions hold up better To a hammer than others.

I wouldn't characterize that as 'destroyed', but then I am used to having to reassemble fossils. (Destroyed would be irretrievable.) I would think it could work if you were very careful as to the placement of the chisel... I've done this, not with Mazon stuff but other similar fossils, and have been lucky.

If you got it that far with a hammer, the prospects look good. I would not have expected a long concretion break cleanly with a hammer anyway.

[Nimravis]

5 hours ago, Wrangellian said:

I wouldn't characterize that as 'destroyed', but then I am used to having to reassemble fossils. (Destroyed would be irretrievable.) I would think it could work if you were very careful as to the placement of the chisel... I've done this, not with Mazon stuff but other similar fossils, and have been lucky.

If you got it that far with a hammer, the prospects look good. I would not have expected a long concretion break cleanly with a hammer anyway.

Long concretions can and do break cleanly with a hammer- (Large concretion in the center I opened with a hammer).

 

 

If I thought that the broken concretion contained an animal I would not have used a hammer, but due to it's shape and the fact that I got it from Pit 4, I knew with out a doubt that it was a fern. The one thing that was different with this concretions was the sound that was made when I lightly tap it. This one had a high pitch versus the sound that come from other Mazon Creek concretions- a lower pitch thump sound. I know it sounds funny, but that is one of the ways that I and other collectors could tell in a muddy area, if we found a concretion or a rock. Due to the make up of this concretion, I would not want to try to chisel anything off of it.

[Peat Burns]

Informative post and beautiful specimens. Thanks for posting

[Nimravis]

2 hours ago, Peat Burns said:

Informative post and beautiful specimens. Thanks for posting

I’m glad you liked it PB

[Nimravis]

On 10/16/2017 at 2:47 AM, smt126 said:

Do you have any before and after pictures of cleaning them? The ones I have I never know if I should leave them alone or try to scrub them up some.

Per your request- Here is a fern before and after.

 

[Rob Russell]

Great post, and a very nice collection!  Thanks for sharing!

[Nimravis]

3 hours ago, Rob Russell said:

Great post, and a very nice collection!  Thanks for sharing!

Thanks Rob

[Captain America]

Excellent post and fantastic photographs!

 

I'm in Ottawa, 20 or so miles west of this area, and my family and I were disappointed about six years ago when we went to the state park fossil area and it was covered over in vegetation, and as flat as if a bulldozer had run it over. I'm hoping to find some good locations elsewhere in the area.

 

One other idea I've got is to check spoils of coal mines in La Salle County. The very first fossil I found was years ago in Wenona, IL at the coal mine's spoil pile. There are piles around where we are: Ladd, Seatonville, Cherry, La Salle, etc.

 

I'm amazed at the quantity of concretions that must have been collected over the past 100 years!

[Nimravis]

10 hours ago, Siwash said:

Excellent post and fantastic photographs!

 

I'm in Ottawa, 20 or so miles west of this area, and my family and I were disappointed about six years ago when we went to the state park fossil area and it was covered over in vegetation, and as flat as if a bulldozer had run it over. I'm hoping to find some good locations elsewhere in the area.

 

One other idea I've got is to check spoils of coal mines in La Salle County. The very first fossil I found was years ago in Wenona, IL at the coal mine's spoil pile. There are piles around where we are: Ladd, Seatonville, Cherry, La Salle, etc.

 

I'm amazed at the quantity of concretions that must have been collected over the past 100 years!

I have heard that there are areas in LaSalle County to collect , but I have never looked there. My Mazon Creek Fossil mentor would tell me when he would collect with Francis Tully, the person that the Tully Monster is named after, they would trip over concretions because there were so many. Back then, he would not freeze and thaw them, they would crack them open in the field and if the fossil was not perfect or to their liking they would just leave them. 

 

Let me know how you do in LaSalle County. 

[Tidgy's Dad]

Thank you for this marvelous, interesting and informative post, Ralph. 

Some of those specimens are truly incredible and very, very beautiful. 

 

[fossilized6s]

You've collected some beautiful pieces over the years, Nimravis. And i'm sure these are just the tip of the iceberg.

 

I only started collecting the Francis Creek shale since 2014, but I've been there about 50-60 times.....ish. And I've learned a lot and found some nice stuff. But i would give anything to hunt it a decade to two decades ago.