Reinterpretation of section of Cretaceous rocks in Alamosa Creek Valley area, Catron and Socorro counties, New Mexico

Winchester's (1920) Bell Mountain sandstone member at the top of his Miguel formation in the Alamosa Creek Valley area, Socorro and Catron counties, New Mexico, is the upfaulted duplication of his Gallego sandstone member, from which it had been supposed to be separated by nearly 1,000 feet of beds. Winchester's names, Miguel formation, Chamiso formation (for the Mesaverde rocks overlying the Miguel formation), and Bell Mountain sandstone member, are abandoned and stratigraphic names used in the San Juan Basin are extended to the units recognized in the Alamosa Creek Valley. The marine shale tongue of the Mancos shale (Pescado tongue of Pike, 1947) underlying the Gallego sandstone member, now of the Gallup sandstone, is shown to be of latest Carlile age, although it contains some species heretofore regarded as indicative of Niobrara age. The name D-Cross tongue of the Mancos shale is proposed for this marine shale unit, which may be a somewhat higher and younger tongue than the Pescado tongue of Pike at the type locality. The lower part of the Gallup sandstone of the Alamosa Creek Valley area, of middle to late Carlile age, tongues out into the Mancos shale in the southeastern part of the Mount Taylor coal field.