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I've been interested in comparing the various locations where Pennsylvanian siderite fossils are found. So I've decided to collect the information I have so far into this topic. This is based on bits of information that I could find and may need corrected.

Feel free to add images of your fossils from any of these locations. And If you have other locations to add, please do. I'll add those into this first post.

Nodules at these locations are all similar to those found at the well-known location of Mazon Creek in Illinois. Nearly all locations are in the gray shale directly above the coal so they each occur at the same point in each of their cyclothems--as the coal forest is being inundated with the rising ocean levels. Each cyclothem is the result of regular glacial and interglacial periods lasting about 100,000 or so years. cyclothem that I'm working on....


Approximate ages are very rough, based on the number of cyclothems between each formation. Here's a graphic of a

Here's the list from oldest to youngest formations with some images and references.


Mansfield formation??

Aprox. age: 315-320 mya




Photos from linked paper on Crockhey

UK--Crockhey Opencast

Aprox. age: 315 mya??? (Westphalian A)

overlying: Wigan Coal

Paper on Crockhey Fossils




Stanley Cemetery Flora / Brazil Formation

Aprox. age: 313 mya

overlying: Lower Block Coal/ Tartar

Location: Green and Vigo County, Indiana

Brazil Formation of Indiana

Stanley Cemetery Flora of Greene County



Mazon Creek / Francis Creek Shale

Aprox. age: 309 mya

overlying: Colchester Coal

Location: Grundy County, Illinois



Photo from Collection of Missourian

Knob Noster, Missouri

Aprox. age: 309 mya

overlying: Croweburg Coal

Location: Knob Noster, MO



Okmulgee, Oklahoma

Aprox. age: 309 mya

overlying: Henryetta Coal

Location: Okmulgee, OK

The Okmulgee, Oklahoma fossil flora, a Mazon Creek equivalent



Energy Shale

Aprox age: 306.5 mya

overlying: Herrin Coal

Carterville and Georgetown, Illinois

A middle Pennsylvanian fern from Carterville, Illinois

Herrin Quadrangle Map with Notes about Energy Shale



Chieftain No. 20 Flora / Dugger Formation

Aprox. age: 305.5 mya

overlying: Danville Coal / Coal VII

Vigo County, Indiana

Chieftain No. 20 Flora (Middle Pennsylvanian) of Vigo County, Indiana

Edited by Neophytus Elginian
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The Lawrence Formation near Lawrence, Kansas has produced siderite concretions containing horseshoe crabs and spiders, at least. I have not had the pleasure of finding any myself, though.

Also, would you include the arthropod-bearing concretions from the UK?

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Here's a paper I found that gives an overview of the siderite locations in US and Europe.

Carboniferous plants preserved within sideritic nodules – a remarkable state of preservation providing a wealth of information

Looks like I should include the UK locations, France, Poland and Nova Scotia.

It appears that the siderite formation is a pretty common occurrence in the Pennsylvanian. And usually at the same point in the cycle. I assume that it has something to do with the unique anoxic condition of decomposing peat from the coal forest being buried suddenly by salt water and sand.

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I've added Crockhey, UK with some info I could find.

And a link to a webpage of photos of some of Terry Dactyll's finds I think.

Edited by Neophytus Elginian
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In N.W. Pennsylvania, east of Allegheny National Forest and south of Smethport, there is a small, flooded strip mine (a few miles from our family camp), last active 100 years ago (supplying coal to the tram railroad that was hauling the last of the Black Forest to the mills). It is hopelessly overgrown now, but 50 years ago the spoil area (circled) was loaded with coal-swamp trunks & roots, and innumerable siderite concretions. Splitting these nodules yielded a recognizable fossil about one time in ten, and while being no where near the quality of preservation of Mazon Creek concretions, they were the subject of endless summer days of fascination by this young boy. :)


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On page 78 from the book, "Pennsylvanian Fossils of North Texas", that

at the lower portion of the Finis Shale from the base of the hillside at

Jacksboro, both siderite and phosphatic nodules are found. It's the Finis Shale member

overlying Jacksboro Limestone Member of the Graham Formation. That could be safely added to

your list I would think.

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  • 2 weeks later...

I have heard of siderite occuring in Warren and McKean counties (Allegheny National Forest), and other locations near the Allegheny Resevoir.

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It is a great shame that Crock Hey is now gone.

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