Chalk Butte Formation | |
---|---|
Stratigraphic range: Tortonian-Zanclean (Hemphillian) ~ | |
Type | Formation |
Thickness | About 538 feet |
Lithology | |
Primary | Tuffaceous sandstones, siltstones, conglomerates |
Other | Tuff, ash beds, freshwater limestone |
Location | |
Coordinates | 43°36′N 117°30′W / 43.6°N 117.5°W |
Approximate paleocoordinates | 44°18′N 114°36′W / 44.3°N 114.6°W |
Region | Malheur County, Oregon |
Country | ![]() |
Type section | |
Named for | Chalk Butte |
The Chalk Butte Formation is a geologic formation in Oregon, which forms a part of the Idaho Group.[1] It preserves fossils dating back to the Neogene period.[2] It was proposed along with the Grassy Mountain Basalt Formation and the Kern Basin Formation as a division of the Idaho Group rocks in the Mitchell Butte Quadrangle.[3] The predominant rock types are tuffaceous sandstones, siltstones, and conglomerates with smaller amounts of tuff, ash beds, and freshwater limestone.[3] A partial section at the type location determined the formation to be about 538 feet thick.[3]
The following fossils have been reported from the formation:[2][4]