Boquillas Formation

The Boquillas Formation is a geologic formation deposited during the Late Cretaceous in modern-day West Texas. It is typically composed of alternating marls and limestones with thin volcanic ash beds (bentonites). It was named for outcrops near the former Boquillas post office in Big Bend National Park.^[2] The term Boquillas Formation has been used for rocks that outcrop from Del Rio, Texas to as far west as Doña Ana County, New Mexico.^[3]

Boquillas Formation
Stratigraphic range: Cenomanian to Santonian
Limestone of the Boquillas Formation in Big Bend National Park
Type	Formation
Unit of	Eagle Ford Group / Terlingua Group
Sub-units	Ernst Member, San Vicente Member, Terrell Member, Lozier Canyon Member, Antonio Creek Member, Scott Ranch Member, Langtry Member[1]
Underlies	Austin Chalk or Aguja Formation
Overlies	Buda Limestone
Lithology
Primary	Marl
Other	Limestone, volcanic ash beds
Location
Region	West Texas
Country	United States
Type section
Named for	Boquillas post office, Big Bend National Park, Texas[2]
Named by	J. A. Udden[2]

Boquillas Formation - stratigraphy

Vertebrate fossils found in the Boquillas Formation include mosasaurs, fish bones, and shark's teeth.^[4][5] Invertebrate fossils found in the formation include ammonites, swimming crinoids, inoceramid clams, sea urchins, oysters, and foraminifera^[1]