Adrian P. Hunt

Coastal environments of the Pictured Cliffs Sea were from northwest to southeast, deltaic, barrier shoreline, and tidal flat. The major source area was southeastern Arizona. The shoreline trend was northwest-southeast, but a major deflection occurred during Didymoceras cheyennense time reflecting the beginning of a volcanic uplift in southwestern Colorado. This new uplift started contributing sediment to the Basin in upper Fruitland time, in the northwest of the area, in the form of airfall ash, and during Kirtland time became the dominant source area. The Farmington Sandstone is a clastic wedge of braided stream material eroding this uplift. The Animas Formation represents the final erosion of this highland, producing rhyolitic and andesitic debris. This highland is now only represented by a few laccoliths, and the Cimarron Ridge Formation. The Ojo Alamo Sandstone also derives from this uplift. The unconformity at the base of the Ojo Alamo is not angular, evidenced by depositional thinning from northwest to southeast, intraformational unconformities in the Fruitland-Kirtland in the southeast and subcontinuity of a volcanic-rich facies, locally termed the Naashoibito, from Farmington to Cuba. The hiatus represented by the unconformity is of short temporal duration. In the northwest of the area there is an upward coarsening sequence from suspended load-mixed load-bed load streams from Fruitland to Ojo Alamo, reflecting increased er osion of an active tectonic high. Virtually all pre-Naashoibito vertebrate fossils are restricted to upper delta plain-lower alluvial plain facies behind the major delta in the northwest of the area.

1983 New Mexico Geological Society Annual Spring Meeting April 29, 1983, Macey Center Online ISSN: 2834-5800

Pages: 15-16