New Mexico Geological Society Annual Spring Meeting — Abstracts

Ammonites and other molluscs were collected from near the base of the Point Lookout Sandstone near Cabezon, New Mexico. The ammonites Placenticeras syrtale, Baculites sp. and Scaphites leei III, the gastropod Gyrodes sp. and other unidentified gastropods, and the bivalves cf. Tellina sp., cf. Siliqua sp., cf. Mactra sp., Cardium sp., inoceramids and other bivalve taxa were recovered. In 1917, W. T. Lee reported a locality near Cabezon where the old wagon road crossed the top of the Mancos Shale. He collected a small molluscan fauna from what he called the transitional zone between the uppermost Mancos Shale and the basal Mesaverde. We believe that the horizon we collected--a fossiliferous, calcareous sandstone ~ 6 m above the base of the Point Lookout Sandstone--is the same horizon collected by Lee. Lee’s list included the bivalves Ostrea elegantula, Anomia sp., Pinna sp., Cardium sp., Cyprimeria sp., Tellina sp., Liopistha undata, Mactra sp. and Corbula sp. as well as the gastropods Gyrodes sp. and Actaeon sp. But, he did not report Scaphites or Baculites from the locality. The only ammonite he reported was Placenticeras sancarlosense, a species subsequently synonymized with P. syrtale.

P. syrtale also occurs in the Dalton Sandstone in the Cabezon area. It has also been reported from the upper part of the Mancos Shale in the upper Rio Grande Valley and along the western side of the Sierra Nacimiento, including the Satan Tongue of the Mancos Shale near La Ventana. P. syrtale has been reported to range from the lower Santonian to the lower Campanian. The Baculites specimens collected from the Point Lookout Sandstone near Cabezon are closest to variants of Baculites aquilaensis in their prominent arcuate nodes on the outer flanks. B. aquilaensis var. obesus was reported by Reeside from the basal part of the “Mesaverde Formation” east of Cuba, New Mexico. Scaphites leei III has also been reported from near the base of the “Mesaverde Formation” east of Cuba and from the Hagan coal field. This would correspond to the base of the Point Lookout Sandstone. S. leei III has also been reported from the upper part of the Mancos Shale on the eastern side of the San Juan Basin and from the Ortiz Mountains. S. leei III is the lowest Campanian Zone taxon. This indicates an earliest Campanian age for the Point Lookout Sandstone near Cabezon.