Palomas Formation


The Palomas Formation is a geologic formation exposed in the southern Rio Grande rift of New Mexico. It preserves fossils dating back to the Pleistocene to Quaternary.

Description

The formation is composed of beds of poorly cemented conglomerate, sandstone, and siltstone, with a total thickness of. The formation is better cemented to the west, where it resembles the Gila Formation. The formation includes both piedmont and axial river facies. The conglomerate is gray to brown, poorly to moderately sorted, and contains clasts of tuff, basalt, rhyolite, and andesite up to long. The siltstone is well-sorted and trough-crossbedded. The formation may correlate with the Sierra Ladrones Formation to the north and the Camp Rice Formation to the south. The age is estimated as 5 Ma to 0.4 Ma.
Basalt flows lying on a geomorphic surface cut in the formation yield a radiometric age of 2.1 and 2.2 Ma.

Fossils

The lower part of the formation contains fossil mammals and reptiles, including turtles, lizards, snakes, rabbits, rats, gophers, mastodons, horses, and deer. Paleomagnetic dating gives an age for this bed of 4.05 to 4.20 Ma.

History of investigation

The unit was first named the Palomas Gravel by C.H. Gordon in 1907. It was renamed the Palomas Formation and assigned to the upper Santa Fe Group by Lozinsky and Hawley in 1986. However, Reppening and May regard it as post-Santa Fe.

Footnotes