Baca Formation

Baca Formation
Stratigraphic range: Eocene PreꞒ Ꞓ O S D C P T J K Pg N
Red beds of the Baca Formation in the Sawtooth Mountains of New Mexico
Type	Formation
Underlies	Spears Formation
Overlies	Mesaverde Group
Thickness	694 feet (212 m)
Lithology
Primary	Conglomerate
Other	Sandstone, claystone
Location
Coordinates	34°19′55″N107°16′19″W / 34.332°N 107.272°W / 34.332; -107.272
Region	New Mexico
Country	United States
Type section
Named for	Baca Canyon
Named by	R.H. Wilpolt et al.
Year defined	1946
Baca Formation (the United States) Show map of the United States Baca Formation (New Mexico) Show map of New Mexico

The Baca Formation is a geologic formation in southern New Mexico and Arizona. ^[1] It preserves fossils dating back to the Eocene period. ^[2]

Description

The formation consists of coarse conglomerate, red and white sandstone, and red clay. Its total thickness is 694 feet (212 m), of which 80–140 feet (24–43 m) is conglomerate. ^[1] The formation rests unconformably on the Cretaceous Mesaverde Group and is overlain by the Oligocene Spears Formation. ^[2]

The formation was deposited in a basin that developed in Eocene time in eastern Arizona and west-central New Mexico. The basin was mostly a system of braided streams subject to frequent flash floods, with meandering streams restricted to the easternmost part of the basin. Paleocurrent directions showed that stream flow was generally to the east-northeast. Shallow floodplain lakes and a large, shallow closed lake in the eastern part of the basin were also present, though lacustrine beds are nearly absent due to extensive river delta formation. ^[3] Deposition ended with the eruption of the Mogollon-Datil volcanic field, which disrupted the Baca drainage and buried the basin in volcaniclastic rock. ^[4]

Fossils

The formation is relatively poor in vertebrate fossils, and only six of biostratigraphic significance have been found. These are the titanotheres Paleosyops and Manteoceras , an artiodactyl fossil trackway and Protoreodon fossil, and a small mammalian fauna at Mariano Mesa. The titanotheres are characteristic of the Bridgerian age while the trackways indicate a late Eocene age or younger. ^[2]

History of investigation

The formation was first described by R.H. Wilpolt and his coinvestigators in 1946 and named for exposures in Baca Canyon in the Bear Mountains. ^[1]

See also

• Earth sciences portal
• Paleontology portal

• List of fossiliferous stratigraphic units in New Mexico
• Paleontology in New Mexico

Footnotes

1. Wilpolt et al. 1946.
2. Lucas et al. 1981.
3. Cather & Johnson 1984.
4. Love 1989.

References

• Cather, S.M.; Johnson, B.D. (1984). "Eocene tectonics and depositional setting of west-central New Mexico and eastern Arizona". New Mexico Bureau of Mines & Mineral Resources Circular. 192. Retrieved June 24, 2021.
• Love, D.W. (1989). "Bidahochi Formation; an interpretive summary" (PDF). New Mexico Geological Society Field Conference Guidebook. 40: 273–280. Retrieved October 8, 2020.
• Lucas, Spencer G.; Schoch, Robert M.; Manning, Earl; Tsentas, Costgas (1981). "The Eocene biostratigraphy of New Mexico". Geological Society of America Bulletin. 92 (12): 951. Bibcode:1981GSAB...92..951L. doi:10.1130/0016-7606(1981)92<951:TEBONM>2.0.CO;2.
• Wilpolt, R.H.; MacAlpin, A.J.; Bates, R.L.; Vorbe, George (1946). "Geologic map and stratigraphic sections of Paleozoic rocks of Joyita Hills, Los Pinos Mountains, and northern Chupadera Mesa, Valencia, Torrance, and Socorro Counties, New Mexico". U.S. Geological Survey Oil and Gas Investigations Preliminary Map. OM-61. Retrieved July 31, 2020.