Abstract

The Trinidad Sandstone, a correlative of the lower Fox Hills of the Western Interior and the Pictured Cliffs Sandstone of the San Juan Basin area, was deposited in Late Cretaceous time on an eastward-prograding shoreline. Depositional framework was in shallow neritic and beach environments during the final transition from marine to continental conditions as the Cretaceous sea retreated from New Mexico and Colorado. The Trinidad conformably overlies the Pierre Shale, and is successively overlain by the coal-bearing Vermejo (Cretaceous) and Raton (Cretaceous-Paleocene) Formations. The Trinidad intertongues with the Vermejo Formation along the southern margin of the Raton Basin between Dawson and Cimarron, New Mexico. This intertonguing represents local transgressions during the withdrawal of the sea. The Trinidad ranges from 0-130 feet thick in the New Mexico portion of the Raton Basin and consists mostly of very fine- to medium-grained sandstone. Linear inorganic sedimentary structures include ripple marks, crossbedding, channel-fill structures, parting lineation, and crumpled and contorted bedding.

Ophiomorpha is the most abundant organic sedimentary structure (trace fossil) in the Trinidad. Aulichnites, Asterosoma, Teichichnus, Diplocraterion, Desmograpton, and other unidentified tracks and trails are common throughout the formation in outcrops from Cimarron to Raton, New Mexico. These trace fossils are unique to the Trinidad in rocks younger than Pierre Shale in this area, and serve to distinguish sandstones of the Trinidad from lithologically similar continental sandstones of overlying formations both at the outcrop and in drill cores.