Diagenesis of a mixed arenite petrofacies, Lobo Formation (Tertiary), southwestern New Mexico
— W. C. James and J. F. Russo

The Lobo sandstones are divisible into four petrofacies based on framework composition: (1) sedarenite, (2) arkose, (3) volcanic arenite and (4) mixed arenite. The mixed arenite, a hybrid of the other petrofacies end members, is composed of subequal amounts of quartz (43%), feldspar (25%) and lithic fragments (32%). Limonite, smectite and calcite are the principal authigenic products found in the mixed arenite with calcite predominant. The mixed arenite is also a hybrid among petrofacies in terms of its diagenetic constituents. It is more closely aligned, both in terms of grain types and diagenetic components, to the sedarenite and volcanic arenite. These compositional relations suggest a strong influence of starting grain composition on diagenesis. Moreover, despite considerable diagenetic modification, the provenance imprint associated with sandstones of the Lobo has clearly not been significantly diminished.