New Mexico Geological Society Annual Spring Meeting — Abstracts

The geology in areas underlain by Middle to Upper Pennsylvanian sedimentary rocks along the eastern sides of the Sandia and northern Manzano (Manzanita) Mountains has been depicted in contemporary geologic maps using an informal and very loosely applied stratigraphic nomenclature that has seen little change since the mid-20^th century. For instance, recent STATEMAP efforts in the Sandia Mountains have tended to treat the marine to marginal-marine Pennsylvanian section as consisting of a relatively thin basal sequence of siliciclastic-dominated deposits (Sandia Formation), and a considerably thicker, overlying succession of undifferentiated limestone and silciclastic deposits (Madera Formation or Group). In recent years the stratigraphy of correlative strata elsewhere in New Mexico has been subjected to intensive study on a regional scale, and a reference section for rocks of Pennsylvanian age has been established nearby in the Manzanita Mountains near Tijeras, New Mexico at Cedro Peak (see Lucas et al., 2014: New Mexico Geology, v. 36, no.1). We have recently begun work to characterize the stratigraphy of Pennsylvanian strata 14 km to the north of Cedro Peak, in the Sandia Mountains, with initial results indicating that the formation-rank, and in most cases the member-level nomenclature that has been established to the south is readily applied to these rocks. Thus, the Sandia, Gray Mesa, Atrasado, and Bursum formation lithostratigraphic units of the “new” nomenclature may now be applied in the Sandia uplift. Geologic mapping of a small area (~4 km²) along Highway 536 (Sandia Crest road) conducted during visits last year show that this nomenclature is amenable to 1:24,000 scale mapping, and that significant improvements in the interpretation and depiction of geologic structures in the East Mountains should be possible through an awareness and willingness to apply the results of recent stratigraphic studies of the Pennsylvanian System in New Mexico. Work is underway to provide a detailed characterization of the stratigraphy of these rocks in the Sandia Mountains including lithostratigraphy, biostratigraphy (age), and associated interpretations (e.g., inferences regarding tectonic vs. glacioeustatic controls over mid- to late-Pennsylvanian deposition in the region).