Cody Shale facts for kids

The Cody Shale is a special type of rock layer. Geologists call it a geologic formation. It formed a very long time ago, during the Late Cretaceous period. This was the time when dinosaurs still roamed the Earth!

You can find the Cody Shale in parts of the United States. It is mapped in the states of Wyoming, Idaho, and Montana.

What is the Cody Shale Made Of?

The Cody Shale is mostly made of shale. Shale is a type of sedimentary rock that forms from mud and clay. These tiny bits settle in layers over millions of years.

Scientists have studied the Cody Shale closely. W.G. Pierce described it as having two main parts. The upper part is a buff, sandy shale. It also has thin layers of buff sandstone. The lower part is a dark gray, thin-layered marine shale. This means it formed in the ocean.

Different Parts of the Cody Shale

Geologists often divide large rock formations into smaller parts. These smaller parts are called "members." The Cody Shale has many different members. They can change depending on where you are looking.

Here are some of the members found within the Cody Shale:

• Ardmore Bentonite Beds (Wyoming)
• Belle Fourche Member (Montana, Wyoming)
• Carlile Member (Montana, Wyoming)
• Claggett Member (Montana, Wyoming)
• Eldridge Creek Member (Montana)
• Gammon Ferruginous Member (Montana, Wyoming)
• Greenhorn Calcareous Member (Montana)
• Niobrara Member (Montana, Wyoming)
• Sage Breaks Member (Wyoming)
• Shannon Sandstone Member (Montana, Wyoming)
• Steele Member (Wyoming)
• Sussex Sandstone Member (Wyoming)
• Telegraph Creek Member (Montana, Wyoming)
• Wallace Creek Tongue (Wyoming)

Sometimes, a member of one formation can be important enough to be called its own formation in other places. For example, the Greenhorn is a member of the Cody Shale in Montana. But in states like Colorado and Kansas, the Greenhorn is considered a separate formation all by itself!