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Pierre shale fossil finding


IonRocks

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After practically years of scouting properties in my area, I’ve finally found a decently productive site.

To start, will just be some neat info about the site. 

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It’s relatively difficult to find nice exposed rock on the prairie.

These areas are generally called barrens, and are interestingly home to some unusual plants which grow in cracks in the rocks. They are also frequented by rattlesnakes, burrowing solitary bees, and lizards.

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In my experience the best way to find these is a mixture of roadside observation and satellite imagery. 

This particulars site was only visible on satellite.

Typically these areas look like this.

 

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The next step in this case was to get a better view of the site.

Luckily I was friendly with the owner of a neighboring property, and could observe from a distance that the area was not entirely eroded sands, and contained good amounts of splitting rock.

For this particular area it was relatively viral that the rock be partially eroded and splitting. The sites with more eroded rock consist mainly of shell fragments in sand, while the less eroded rock is too difficult to break up and locate fossils within without causing major damage.

 

Pictured: specimens from a similar site.

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Interesting, do you know the age and name of the exposure?  (Oh, my aging eyes/brain - I see the title says Pierre shale.  That was what I was guessing from the look of the specimens.)  I'm guessing you are in eastern Co.

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Yes, eastern Colorado, the “Upper Unit” of the Pierre shale.

In many areas where the rock is not eroded, specimens mostly turn out like this. Many pieces and a lot of glue required. Often half of the fossil is lost while breaking rock.

 

 

To make my trip easier, my County has a neat database and map of land owners. So some quick interneting allowed me to find where I was addressing my letter for access to the site. In this case, the land has been unoccupied and unused for about 60 years, with the owners being in a different state.

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  • 5 months later...

Most of the shells are very eroded. Rarely one can find shell with some of the exterior intact.

 

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I am of course always hoping I will find a very unlikely vertebrate fossil, but, only ever find modern bones and bone like rocks 35C208A5-7CED-4EB6-9A95-49CDB33053D1.thumb.jpeg.3704689e1ab815698808bfdc998e786e.jpeg

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Sometimes the hard work of research and prospecting pay off. I hope you find some ammonites too!

-Dave

__________________________________________________

Geologists on the whole are inconsistent drivers. When a roadcut presents itself, they tend to lurch and weave. To them, the roadcut is a portal, a fragment of a regional story, a proscenium arch that leads their imaginations into the earth and through the surrounding terrain. - John McPhee

If I'm going to drive safely, I can't do geology. - John McPhee

Check out my Blog for more fossils I've found: http://viewsofthemahantango.blogspot.com/

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Here is a nearly perfectly preserved shell.

I have certainly acquired many more larger shells like this, hidden within the mass mortality rocks. Unfortunately, I have not yet found a good way to prepare them, as the shell does not separate from the rock well.

 

Currently one of my goals is to locate a gastropod mass mortality pocket. I know they exist in the area as I have found small pieces of them, but have not yet found the source.

 

interestingly enough, the four masses of shells in this post were found within 20m of each other. I suspect that with some digging I can locate bedrock full of the things. 

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Your sites and the bivalves you are finding remind me of teepee buttes one can find abundantly in the Pierre shale south of Colorado Springs and around Pueblo, Colorado, but on a smaller scale.  Teepee buttes are masses of limestone that formed where methane was venting from the sea floor.  Mostly the Pierre Shale is easily eroded shale (duh!), so as it erodes to a flattish plain the more resistant limestone masses are left standing out as teepee-shaped small hills.  Here is a reference that describes the buttes.  The methane seeping from vents in the sea floor supported a specialized community of bacteria that, on one hand, caused chemical changes that drove the precipitation of calcium carbonate (limestone), and on the other hand fed and supported a community of animals (bivalves mostly, but also gastropods, cephalopods, crabs, tube worms etc) that only lived on these carbonate mounds on an otherwise almost barren mud sea floor.  Many of your bivalves seem to be Nymphalucina, a specialist bivalve that is only found associated with methane seeps in the Pierre Shale.  If the methane seeps were small or didn't last too long, they might only cause the formation of large carbonate concretions instead of a full-blown "teepee". 

 

Don

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1 hour ago, FossilDAWG said:

Your sites and the bivalves you are finding remind me of teepee buttes one can find abundantly in the Pierre shale south of Colorado Springs and around Pueblo, Colorado, but on a smaller scale.  Don

Well, now you have made me quite suspicious of a couple hills I have not yet visited. 

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11 minutes ago, will stevenson said:

What’s this? It looks like opal or is it just water reflecting something?

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Yes, the shells sometimes have opalescent sections. Most often baculites have its

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I should mention that there are also a couple of horizons within the Pierre Shale in the Fort Collins area that are sandy enough to termed sandstone members, and they may contain sandy concretions with fossils.  An example would be the relatively resistant layer that forms Fossil Ridge on (as I recall) the south side of town.  This is quite different from the teepee butte horizons as the layer is continuous and does not have an obvious carbonate component.  A long time ago (1992 I think) I was in Fort Collins for a bit taking a summer course at the university there, and I escaped for a few hours to explore around the area.  I drove around the fossil ridge area hoping to see an outcrop or something that I could explore.  As it happens I came across a place where a homeowner was putting in a swimming pool and had dug up a pile of sandy shale with a lot of concretions.  After securing permission I loaded my minivan up with several dozen concretions to split later when I got home.  Mostly they turned out to contain Inoceramus clams, which were nice (many had both shells together), but I didn't need 20 of them.  Some contained a variety of small clams, and there was one large gastropod that didn't prep out too well as the shell stuck to the rock.  I only found one tiny piece of an ammonite.  However, I mention this because there are a number of possibilities for collecting in the Pierre Shale in the area, and the fauna varies from site to site depending on the exact layer and the local environment at the time the rock was deposited.

 

Don

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Finding new places to explore is half the fun of collecting fossils.  Nice detective work.  

 

I don't know if FossilDAWG is onto something or not, but I have found hundreds of concretions that are full of small clams that may or may not be the seep genus Nymph..etc.   In any case these areas can be good for ammonites.  

 

The best way to prep these nice little snails is with a microscope and a small air scribe.  

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  • 2 months later...

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