Hidalgo Formation

The Hidalgo Formation is a geologic formation of Maastrichtian age (latest Cretaceous)^[1] in southwestern New Mexico.^[2] It is of interest to geologists for the clues it preserves of the nature of Laramide deformation in the latest Cretaceous.^[3]

Hidalgo Formation
Stratigraphic range: Maastrichtian ~70.53–71.44 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Underlies	Rubio Peak Formation
Overlies	Ringbone Formation, Skunk Ranch Formation
Thickness	7,500 feet (2,300 m)
Lithology
Primary	Basalt, andesite
Other	Volcaniclastics, limestone, shale
Location
Coordinates	31.847°N 108.457°W / 31.847; -108.457
Region	New Mexico
Country	United States
Type section
Named for	Hidalgo County, New Mexico
Named by	S.G. Lasky
Year defined	1938
Hidalgo Formation (the United States) Show map of the United States Hidalgo Formation (New Mexico) Show map of New Mexico

Description

The formation is mostly basalt^[4] or andesite^[5] lava flows, but with some interbedded breccia and pyroclastic rock and, in some locations, up to 200 feet (61 m) of limestone and shale. The formation rests unconformably on the Ringbone Formation^[4] or Skunk Ranch Formation,^[6] and varies greatly in thickness, from 900 to 5,000 feet (270 to 1,520 m).^[4] Argon-argon dating gives a consistent age between 70.53 and 71.44 million years.^[7] The formation is overlain by the Rubio Peak Formation.^[6]

The formation is interpreted as a volcanic center located inland of the southwest coast of the Ringbone depositional basin^[4] that erupted during Laramide tectonic deformation that partitioned the basin.^[8] It may correlate with the Salero Formation of southeastern Arizona.^[9]

History of investigation

The formation was first named the Hidalgo Volcanics by Samuel G. Lasky in 1978 for outcroups found throughout Hidalgo County, New Mexico.^[4]