Decorah Shale facts for kids
Quick facts for kids Decorah ShaleStratigraphic range: Ordovician |
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Decorah Shale exposed in Decorah, Iowa. The Decorah is gray; above it is the brown Cummingsville Formation.
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| Type | Formation |
| Underlies | Galena Group |
| Overlies | Platteville Formation |
| Location | |
| Country | United States |
| Extent | Minnesota |
| Paleozoic Stratigraphy of the Upper Midwest, USA Dates are approximate, and deposition occurred at slightly different times in different areas |
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Ordovician
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The Decorah Shale is a special type of rock layer that is full of fossils. It is the lowest part of a larger group of rocks called the Galena Group. The Decorah Shale sits on top of the Platteville Limestone and below the Cummingsville Formation. These layers of rock formed from the mud and sand at the bottom of a shallow sea. This sea covered a big part of central North America a very long time ago, during the Ordovician Period.
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What is the Decorah Shale?
The Decorah Shale is a type of shale, which is a soft rock made from compacted mud. It is known for having many fossils, meaning it's a great place to find ancient life! This rock layer tells us a lot about what the Earth was like millions of years ago.
Layers of the Decorah Shale
The Decorah Shale is actually made up of three smaller layers, called "members." Think of them like different chapters in a book, each with its own story. From the bottom layer to the top, they are:
- Spechts Ferry: This bottom layer has a lot of ancient plant and animal material. It suggests that a lot of dirt and mud washed into the sea when this layer was forming.
- Guttenberg: This middle layer has bumpy, chalky beds. It also contains special clay layers called K-bentonite. These clay layers formed from ancient volcanic ash that fell into the sea.
- Ion: This top layer is found mostly in southern Iowa. It has alternating layers of shale (mudstone) and limestone (rock made from sea creatures' shells).
Where Can You Find Decorah Shale?
You can find the Decorah Shale in the Upper Midwest region of the United States. It's especially easy to see in places like the Twin Cities area. When these rock layers are exposed at the surface, it's called "cropping out."
Fossil Hunting in Decorah Shale
Because the Decorah Shale is so full of fossils, it's a very popular spot for people who love to collect them! You can find many different kinds of ancient sea creatures here, including:
- Trilobites: These are ancient sea bugs, like prehistoric cockroaches of the sea.
- Brachiopods: These look a bit like clams, but they are a different type of shelled creature.
- Horn corals: These were solitary corals that looked like a horn.
- Gastropods: These are ancient snails.
- Crinoids: Sometimes called "sea lilies," these animals looked like plants with long stems.
- Bryozoans: These are tiny colonial animals that often look like moss or lace.
- Cephalopods: These are ancient relatives of squids and octopuses, and you might find them in the lower parts of the Decorah Shale.
