New Mexico Geological Society Annual Spring Meeting — Abstracts

The MiddJe Jurassic (Callovian) Todilto Formation outcrops throughout much of northwestern and east-central New Mexico and southwestern Colorado. The Todilto represents a vast, paralic salina. In central part of the basin of deposition the Todilto is comprised of a lower Luciano Mesa Member that is dominated by laminated limestone and an upper Tonque Arroyo Member that is composed of gypsum.

The Luciano Mesa Member locally contains depauperate fauna. Holostean fish are known from several localities in New Mexico including: (1) Bull Canyon, west of Santa Rosa; (2) Warm Springs north of San Ysidro; (3) Lamy; (4) Montezuma; (5) Suwanee near Grants; (6) La Liendre near Las Vegas; (7) Echo Amphitheater, south of Chama; and (8) probably near Acoma. Despite the number of localities only the Bull Canyon area has produced significant numbers of specimens.

We have located a new locality for holostean fish from the Luciano Mesa Member adjacent to Ghost Ranch in Rio Arriba County. Fish fossils occur 2.1 m above the lower contact with the Entrada Fomlation. The fish occur in a 10 cm-thick bed of limestone that fonns a slope break. The matrix is a varved, organic-rich limestone. Beds above and below the fish-level exhibit microfolding ("crinkly" bedding) which is characteristic of parts of the Luciano Mesa Member. The Luciano Mesa Member is 4.55 m-thick at this location.

This locality has not been excavated. Sutface collection has yielded two specimens that are reposited at the Ruth Hall Museum of Paleontology at Ghost Ranch. Both specimens are laterally compressed and the cranial and other areas are covered by matrix. However, based on the morphology of the tail and dorsal fin and the fact that only three species of holostean fish are known from the Todilto, we are confident in assigning these specimens to Todiltia schoewei, This locality has great potential to be a significance source of Jurassic fossil fish specimens.