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 Pliocene 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 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 million years to 0.4 Ma.The formation includes both piedmont and axial river facies. The piedmont facies represents alluvial fans and other sediments deposited at the feet of the mountains surrounding the original depositional basin. The axial river facies represents deposition near the main channel of the ancestral Rio Grande River.
The lower part of the formation contains two nested paleovalleys near Truth or Consequences, New Mexico, recording climate fluctuations that incised and then backfilled the valleys. The first was incised and backfilled between 5.1 and 4.87 Ma, while the second dates to 4.87 to 4.5 Ma. The lack of axial river facies in the Palomas Formation between the Palomas and Mesilla Basins may be due to confinement of flow to narrow paleovalleys in this area.