San Jose Formation facts for kids

Quick facts for kids San Jose Formation Stratigraphic range: Wasatchian ~55.8–50Ma PreЄ Є O S D C P T J K Pg N
San Jose Formation capping Mesa de Cuba, northern New Mexico
Type	Formation
Sub-units	Cuba Mesa, Ditch Canyon, Llaves, Regina & Tapicitos Members
Overlies	Nacimiento Formation
Thickness	430 m (1,410 ft)
Lithology
Primary	Sandstone
Other	Shale
Location
Coordinates	36°17′N 107°04′W / 36.29°N 107.06°W / 36.29; -107.06
Approximate paleocoordinates	41°12′N 91°42′W / 41.2°N 91.7°W / 41.2; -91.7
Region	New Mexico
Country	United States
Extent	San Juan Basin
Type section
Named for	San Jose Valley (36°10′48″N 106°55′37″W / 36.180°N 106.927°W / 36.180; -106.927)
Named by	G.G. Simpson
Year defined	1948

The San Jose Formation is an Early Eocene (Wasatchian in the NALMA classification) geologic formation in the San Juan Basin of New Mexico and Colorado.

Description

Road cut in the San Jose Formation, near Cuba, New Mexico

The San Jose Formation is mostly sandstone but with some mudstone beds. The formation was deposited by high-energy streams on a muddy floodplain that was the last preserved sedimentation episode in the San Juan Basin. Stream direction was from the northwest, north, and east towards the south.

The basal Cuba Mesa Member is found throughout the depositional basin and is a coarse-grained sheet sandstone. The Regina Member is floodplain mudstone and disconnected sheet sandstone that intertongues with the sandstone-dominated Ditch Canyon Member in the northwestern part of the basin and the Llaves Member on the east side of the basin. The uppermost member is the siltstone-dominated Tapicitos Member. The Cuba Mesa Member was deposited during subsidence in the basin center, while the later members were deposited during episodes of monoclinal folding along the Nacimiento Fault on the west escarpment of the Nacimiento Mountains.

Paleontology

The mudstone beds of the San Jose Formation are locally rich in fossils. These include the Almagre and Largo faunas of the early Eocene.

Fossil content

Among others, the following fossils have been reported from the formation:

Mammals

Primates

Artiodactyls

Carnivora

• Vulpavus australis

Cimolesta

• Esthonyx bisulcatus

Ferae

Glires

Hyaenodonta

• Hyaenodontidae indet.

Insectivora

• Apatemys bellulus

Pantodonta

• Coryphodon armatus

Perissodactyla

Placentalia

Taeniodonta

• Ectoganus gliriformis

Theriiformes

• Creodonta indet.

Reptiles

Snakes

Turtles

Lizards

• Paraglyptosaurus cf. yatkolai
• Lacertilia indet.

History of investigation

In late 1874, Edward Drinker Cope was a member of the Wheeler Survey but ignored orders from Wheeler to proceed north from the Chama River to Colorado. Instead, he headed south to explore the area north of the San Pedro Mountains, where fossils had been reported. He found early Eocene fossils in the badlands north of Regina, New Mexico and spent about seven weeks collecting fishes, reptiles, and what was then the oldest known mammal fossils in North America. He also collected the fossil of a giant flightless bird. Cope later wrote his father that this was "the most important find in geology I have ever made".

In 1948, G.G. Simpson visited the same area and assigned the fossil beds to the San Jose Formation. In 1967, the formation was divided (in ascending order) into the Cuba Mesa Member, Regina Member, Llaves Member, and Tapicitos Member.