Benton Shale facts for kids

Quick facts for kids Benton Shale Stratigraphic range: Cretaceous
Gray shale (Benton Shale; Colorado Springs, Colorado)
Type	Formation
Underlies	Niobrara Formation
Overlies	Dakota Sandstone
Lithology
Primary	Shale
Other	Limestone, sandstone, bentonite
Location
Region	Montana, Wyoming, North Dakota, South Dakota, Colorado, Nebraska
Country	United States
Type section
Named for	Fort Benton, Montana

The Benton Shale (also called Benton Formation or Benton Group) is a special layer of rock found in parts of the United States. It stretches across states like Montana, Wyoming, North Dakota, South Dakota, Colorado, Kansas, and Nebraska.

This rock layer holds amazing clues about Earth's past. It contains fossils from the Cretaceous Period, which was a very long time ago when dinosaurs roamed! The Benton Shale is mostly made of a type of rock called shale, but it also has layers of limestone, sandstone, and bentonite.

The name "Benton" comes from Fort Benton, a small city in Montana located along the Upper Missouri River.

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  Cool cone-in-cone shapes found in Benton Shale.

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  A close-up of the gray Benton Shale.

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  Gray shale with layers of bentonite in the Benton Shale.

What is the Benton Shale?

The Benton Shale is a type of geologic formation. Think of it like a giant, flat layer of rock that formed over millions of years. This particular formation is made mostly of shale, which is a fine-grained sedimentary rock. It forms from mud and clay that settled at the bottom of ancient seas.

How it Formed

During the Cretaceous Period, about 100 to 66 million years ago, a huge inland sea covered much of central North America. This sea is known as the Western Interior Seaway. The Benton Shale formed from the mud and silt that collected on the seafloor of this ancient ocean. Over time, these sediments were buried and squashed, turning into the rock we see today.

What We Find in It

Because the Benton Shale formed in an ancient sea, it's a great place to find fossils of marine life. Scientists have discovered many fossils of sea creatures that lived in the Western Interior Seaway. These fossils help us understand what life was like millions of years ago.

Where is the Benton Shale Found?

The Benton Shale is found across a wide area in the central United States. It's a significant rock layer in states like Montana, Wyoming, North Dakota, South Dakota, Colorado, Kansas, and Nebraska. Geologists study these layers to understand the history of the land.

Different Names for the Same Rock

Sometimes, different parts of the Benton Shale are given more specific names. For example, some chalky parts, especially the upper layers, are now called Greenhorn Limestone. Other parts are known as Graneros Shale and Carlile Shale. This is because geologists keep learning more and refining how they classify rock layers. So, while "Benton" is an older term, it still refers to this important group of rocks.

Images for kids

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  Gray Benton Shale

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  An outcrop of the Benton Group in Kansas, identified in 1871.

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  Chalk layers in the Greenhorn Limestone, which used to be part of the "old Benton" classification in Kansas.

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  Chalk layers in the Lower Carlile member, also once considered part of the "old Benton" in Kansas.