New Mexico Geological Society Annual Spring Meeting — Abstracts

The zones of Collignoniceras woollgari,Prionocyclus hyatti, Prionocyclus macombi, Prionocyclus wyomingensis and Prionocyclus novimexicanus are present in the Carlile and Juana Lopez members of the Mancos Shale on the eastern side of Mesa Prieta, Sandoval County, New Mexico. Here, (T16N, R1W) the Greenhorn interval (with abundant Pyconodonte newberryi) is ~ 7 m thick and is overlain by the ~ 60 m thick Carlile Member (locally, no Semilla Sandstone is present) capped by the ~ 36 m thick Juana Lopez Member. The ammonite fauna from the Carlile Member includes Collignoniceras woollgari, Tragodesmoceras carlilense, Romaniceras mexicanum, Herrickiceras costatum, Spathites puercoensis, Prionocyclus hyatti, Placenticeras pseudoplacenta, and Coilopoceras springeri in two assemblage zones, lower (woolgari) and upper (hyatti) separated by ~25 m of section. The ammonite fauna from the Juana Lopez Member includes Prionocyclus macombi, Coilopoceras colleti, Placenticeras sp., Coilopoceras inflatum, Prionocyclus wyomingensis, Scaphites ferronensis, Prionocyclus novimexicanus and Scaphites whitfieldi, from throughout the member.

The Collignoniceras woollgari Zone also occurs at other places in New Mexico including the lower part of the Tres Hermanos Sandstone Member and upper part of the Rio Salado Member at Carthage and the lower Carlile Member at Galisteo Dam. The Prionocyclus hyatti Zone also occurs at other places in New Mexico, including the Carlile Member at Galisteo Dam and the Semilla Sandstone and Carlile members at La Ventana. The Prionocyclus macombi Zone also occurs at many other places in New Mexico, including the type and reference sections of the Juana Lopez at Galisteo Dam and La Ventana, respectively. The Prionocyclus wyomingensis Zone also occurs in the Juana Lopez Member at the type and reference sections, in the D-Cross Member at Cebollita Mesa, and in the D-Cross Member at D-Cross Mountain. The zone of Prionocyclus novimexicanus also occurs at various New Mexico locations, especially in the DCross and Juana Lopez members of the Mancos Shale. The C. woollgari Zone is of early middle Turonian age. The P. hyatti and P. macombi zones are of middle Turonian age, the P. wyomingensis Zone is of late-middle Turonian age, and the P. novimexicanus Zone is of late Turonian age.