| Sentinel Butte Formation | |
|---|---|
|  Stratigraphic range: Thanetian  ~  | |
|   Bentonite (Big Blue Bentonite) in the Sentinel Butte Formation (North Dakota)  | |
| Type | Formation | 
| Unit of | Fort Union Formation | 
| Underlies | Golden Valley Formation | 
| Overlies | Bullion Creek Formation | 
| Location | |
| Region | North Dakota | 
| Country | United States | 
The Sentinel Butte Formation is a geologic formation of Paleocene age in the Williston Basin of western North Dakota. [1] It preserves significant assemblages of non-marine plant and animal fossils.
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