New Mexico Geological Society Annual Spring Meeting — Abstracts

The zones of Prionocyclus wyomingensis, Scaphites ferronensis, and Prionocyclus novimexicanus are present in the D-Cross Member of the Mancos Shale at D-Cross Mountain. The ammonite fauna includes Coilopoceras inflatum Cobban and Hook, Prionocyclus wyomingensis Meek, Scaphites ferronensis Cobban, and Prionocyclus novimexicanus (Marcou). C. inflatum is abundant and is found at or near the base of the D-Cross Member at D-Cross Mountain. All specimens collected are the robust form of C. inflatum. P. w),omingensis, although not common, is found in association with C. inflatum. Thus far, only one specimen of S. ferronensis has been found at D-Cross Mountain. This is the first report of Scaphites occuring at D-Cross Mountain. P. novimexicanus is common and is found in the lower part of the section at D-Cross Mountain, in contrast to Cebollita Mesa and Puertecito, New Mexico, where it is found throughout most of the section of the D-Cross.

The collignoniceratid zone of P. wyomingensis also occurs in the D-Cross Member at Cebollita Mesa, the Juana Lopez Member of the Mancos Shale northeast of Thoreau, New Mexico and in the type section of the Juana Lopez Member northwest of Cerrillos, New Mexico. The occurrence of the standard zone of S. ferronensis at D-Cross Mountain indicates correlation of the lower part of the D-Cross there with the lower part of the D-Cross at Cebollita Mesa, the lowest part of the D-Cross at Puertecito and the upper part of the Juana Lopez Member of the Mancos Shale at the type section. The collignoniceratid zone of P. novimexicanus also occurs in New Mexico in the D-Cross Member at Carthage, Riley, Puertecito, Cebollita Mesa and in the Juana Lopez Member at the type and reference sections. The P. wyomingensis and S. ferronensis Zones are of late middle Turonian age, and the P. novimexicanus Zone is of late Turonian age.