Nacimiento Formation Nacimiento Formation The Nacimiento Formation is a sedimentary rock formation found in the San Juan Basin of western New Mexico (United States) and named for the Nacimiento Mountains. It is a heterogeneous nonmarine formation composed of shale, siltstone, and sandstone, deposited in floodplain, fluvial and lacustrine settings, and made up of sediment shed from the San Juan uplift to the north and the Brazos-Sangre de Cristo uplift to the east. It was deposited mostly between ~64.5 and ~61 million years ago, during the early and middle Paleocene. The climate was humid and warm to hot. This unit interbeds with the
Organ Rock Formation by the Triassic Moenkopi or Chinle Formations by an erosional contact. Toward its eastern extent, the Organ Rock Formation grades into the Cutler Formation, undivided. This transition occurs to the southwest of Moab, UT. The age of the Organ Rock Formation is unconfirmed. The preceding Cedar Mesa Sandstone is dated to the Wolfcampian (ICS stage: Artinskian). The anteceding De Chelly and White Rim Sandstones are dated to the Leonardian (ICS stage: Kungurian). These formations constrain the age of the Organ Rock Formation to the latter part of the Cisuralian Epoch, approximately 290.1 to 272.3 Ma. The Organ Rock Formation may