Chalk Butte Formation

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]

Chalk Butte Formation
Stratigraphic range: Tortonian-Zanclean (Hemphillian) ~10.3–4.9 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Formation
Thickness	About 538 feet
Lithology
Primary	Tuffaceous sandstones, siltstones, conglomerates
Other	Tuff, ash beds, freshwater limestone
Location
Coordinates	43.6°N 117.5°W / 43.6; -117.5
Approximate paleocoordinates	44.3°N 114.6°W / 44.3; -114.6
Region	Malheur County, Oregon
Country	United States
Type section
Named for	Chalk Butte
Chalk Butte Formation (the United States) Show map of the United States Chalk Butte Formation (Oregon) Show map of Oregon

Fossil content

The following fossils have been reported from the formation:^[2][4]

• Antecalomys valensis
• Basirepomys pliocenicus
• Copemys cf. esmeraldensis
• Cupidinimus magnus
• Diprionomys parvus
• Dipoides vallicula
• Eucyon davisi
• Goniodontomys disjunctus
• Hypolagus vetus
• Peromyscus antiquus
• Pliohippus spectans
• Plionictis oregonensis
• Scapanus proceridens
• Dipoides sp.
• Spermophilus sp.
• Camelidae indet.
• Perognathinae indet.
• Soricidae indet.
• ?Vespertilionidae indet.

See also

• List of fossiliferous stratigraphic units in Oregon
• Paleontology in Oregon