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minnbuckeye

Last Autumn, I took a side trip to Graf, Iowa in search of it's "elusive" cephalopods. Fortunately for me, a large piece of rock had released itself from the overhanging cliff and I proceeded to use my sledge hammer on it until broken into eight 50 lb pieces. This then was loaded into my truck without further exploration as I knew, each chunk contained maybe 50 cephalopods within it.  DSC_0496-001.thumb.JPG.a1ba3cc76be4f22d04967781a7e2de8d.JPG

 

 These chunks of matrix were to provide me with a little winter entertainment while the landscape of Minnesota remained white. Two weeks ago I began splitting these boulders, looking for the treasures contained within. At the same time, @Ludwigia posted an image of  belemnites , that made me think how similar his finds were to cephalopods of Graf.

 Acrocoelites (Acrocoelites) gracilis (Hehl in Zieten) ?

<img src='http://www.thefossilforum.com/uploads/gallery/album_1563/gallery_2384_1563_281093.jpg' alt='Acrocoelites (Acrocoelites) gracilis (Hehl in Zieten) ?' title='Acrocoelites (Acrocoelites) gracilis (Hehl in Zieten) ?' data-role='theImage'>          

After complimenting him on his finds, he asked to see my hash plates of Isorthoceras sociale. It is for this reason that I have put a trip report together.

 

This location continues to perplex me a bit. How so many cephalopods over such a long period of time could keep collecting here. From my understanding, Graf, Iowa back in the Ordovician period was a very shallow marine environment where wave action altered how these cephalopod carcasses were deposited. Due to the wave action, many examples of one cephalopod being washed inside the shell of another cephalopod exist.  

2019-03-007.thumb.jpg.b02855ebeb4a2a59acb452c8281fb65c.jpg

 

This is very unique!! The septa of these creatures were thin and broke down readily in the surf, leaving space for other cephalopod shells to be deposited within. To show this better, here is a specimen that had all of it's septa dissolved, but the siphuncle still remained!!! 

DSC_0475-002.thumb.JPG.16f8cb6b3e652aeb2e3886c31d4cc362.JPG 

Another picture showing the decayed cephalopod with remnants of a siphuncle yet no septa

DSC_0479-003.thumb.JPG.4f23daed0e0639b516d45433fdeca113.JPG

 

 

 This I understand. But from my perspective, there are several  odd factors that defy explanation from my limited knowledge with regard to the cephalopod deposition in Graf. The most prominent cephalopod rich rock is a bit orangish in color, as can be seen above.  

 

But there are 2 separate grey/brown zones that the specimens look completely different. First is an area where the cephalopods are flattened like pancakes. If you notice, the gastropods (circled) contain no distortion/ flattening. A mystery to me.

 

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The second darker zone contains cephalopods that are very small in comparison to the orange zone. They reach only about10 -20% of the "normal" size of Isorthocerus socialis found in the orange zone. A different species? Or a stress environment where they just didn't grow well? Obviously the matrix changed, so then should their environment have changed.   An unknown mystery again for me.

 

DSC_0444-001.JPG.8c621736d55dd5d6983eea289b2e083c.JPG 

 

 

 

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minnbuckeye

Here are pictures of typical smaller samples from this site, pieces that break away from the bigger matrix as I try and find large display pieces: v

 

 2019-03-009.thumb.jpg.88fa36fa7ee872f1169763d7baf26010.jpg

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minnbuckeye

2019-03-008.thumb.jpg.fa776d661287a56c8fb02f05a1cb5cef.jpg 

 

Now some death plates. The first is a piece before I work on it (screwdriver, and hammer). Many cephalopods exposed. But improvement to its looks can be had with a bit of work

DSC_0460-002.thumb.JPG.e1b9cdd026ef3d4baaa0082a5e4cc79e.JPG

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minnbuckeye

Now to show Ludwig a few hash plates. These have NOT been prepped yet and should look nicer when done. What needs to be done is remove the cephalopods that stuck to the other side and transfer them over to these pieces. You can see the imprints of the cephalopods I am talking about.

 

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 DSC_0456-001.thumb.JPG.d1f0f6d2697ccfed9e3fdd8e5418892e.JPG 

 

 Just to show that there are fossils other than cephalopods, Here are a few odd ball thins that one could easily overlook.

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minnbuckeye

2019-03-006.thumb.jpg.a39d6649abf0ef031e72c95663035526.jpg 

 

 These TINY gastropods are Murchisdnia. The one below is large in comparison, an ID that I am currently trying to get.

 

DSC_0481-001.thumb.JPG.a1d8c7abd5ee8735b1f08d76a3b749cb.JPG

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minnbuckeye

 

Trilobits from Thelecalymene mammillata found within these blocks. Full trilobites are rare due to the turbulent nature of the shallow environment. Hope you enjoyed this.

 

Mike

 

2019-03-05.thumb.jpg.ead00fb9d5e43ef7d1ce76f10ec2dbc1.jpg

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52 minutes ago, minnbuckeye said:

I proceeded to use my sledge hammer on it until broken into eight 50 lb pieces

 

It sure looks like it was worth the work! Thanks for all these luscious photos.

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@minnbuckeye Fascinating! Thanks for posting this. Perhaps the shallow environment at the time of the deposition of the orange layer was a lagoon which trapped the remains during storm events? As far as I remember, iron deposits can be typical for lagoons. Are oolites visible in the matrix? By the way, my name is Roger, not Ludwig. Ludwigia, as you well know, is my profile name.

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Thanks for posting, it is really a nice site to collect, I have a few blocks of that matrix in my basement from my last trip. If anyone is in the area of that out of the way place you should stop. There is no real parking at this area and it is on a two lane road, so if you pull off, make sure that it is far enough not cause an accident. 

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minnbuckeye
2 hours ago, Ludwigia said:

my name is Roger, not Ludwig

 

I apologize, Roger. When titling this, I meant to come back and finish "Ludwig" with " @Ludwigia" but forgot to. 

 

 Sorry about that,

 Fred  

 

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Tidgy's Dad

Crikey, Fred, what a super report! :)

I'm lucky enough to have one or two of these in my collection thanks to Cedric, @Nimravis, but I didn't know about the different layers and the other species that can be found there. Most splendid. 

Thanks for sharing. 

Cheers,

Maureen. 

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I second that as a great site. I have a huge block that I hope to someday prep sitting out in my garage as well. My who was with me found a full trilobite in that greyer matrix you were talking about. It was probably about 1cm in length. The lagoon theory is definitely an interesting thought. I always just imagine a massive spawn and die migration cycle with this site, floating toward the shoreline.

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Hey, Roger isn't the only one who likes cephalopods! :P

 

Your nautiloids are amazing, Mike - congratulations on finding them, and best of luck with your continued prep on them! 

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minnbuckeye

@Monica, @smt126, @Tidgy's Dad, @Nimravis, @Pagurus, @Ludwigia. Thanks for the wonderful comments. I have been to this site 3 times and many of you probably wonder why I need to go again. It is so prolific. 8 blocks at 50 cephalopods per block is 400 cephalopods (actually 7 blocks, so 350 specimens. I am saving a block for a potential summer visitor). But at the  end of the year, I likely will need more. By the time I donate fossils to schools, nature parks and to anyone having interest in these neat fossils, my supply is depleted!!!

So anyone interested, put your dibs in early! @Ludwigia 

 

Mike

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Mike,

 

I agree with you that this is a great site, here are a couple pics of the site.

 

IMG_1942.jpg.54017cb7d7a5635f4280206f800ea85c.jpgIMG_1975.jpg.490997f4fa5685cd0310ccc6ac824d5c.jpgIMG_1966.jpg.54632fc03154bb1e223a43cd948d7400.jpgIMG_1968.jpg.74b6fbfda57763c1eeb3555eb17272f1.jpgIMG_1969.jpg.9c3b989c599e01b799387dac4d322ae3.jpgIMG_1978.jpg.3906b6ce78411b4694e2aa999a5e348f.jpgIMG_1979.jpg.f4f79cbca05848cd60604402cfc8b31b.jpgIMG_1948.jpg.d355da3348eac5d1e3c28bb7bd3f31f3.jpgIMG_1952.jpg.b32cfc80a6ed2d470b9bba8248702db2.jpg

 

Here is a large piece that I have, and like your's, it is just filled with them and a couple gastropods.

 

IMG_8515.jpg.504366e0b30e7d4c12db767502aa6cb0.jpgIMG_8517.jpg.5b1d94de44e308a103943c1439aadbd8.jpg

 

And a smaller piece that has some nice examples-

 

IMG_8519.jpg.a0449d2ea8655bc79286a6a639ca08e0.jpg

 

 

 

 

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