New Mexico Geological Society Annual Spring Meeting — Abstracts

Recent mapping of the Santa Fe Group near Espanola, N.M., elucidates the stratigraphy of the Espanola Basin and underscores some long-standing problems regarding current stratigraphic nomenclature. The lower 180-200 m of the Chamita Formation type section (CFTS), located southeast of Black Mesa and west of the Rio Grande, is similar to the Cejita Member of the Tesuque Formation, particularly in its fluvial facies and clast composition (corresponding to Lithosome B of Cavazza, 1986). At the CFTS, >200 m of granite-rich piedmont sediment (Lithosome A of Cavazza, 1986) conformably overlies Lithosome B. Biostratigraphic data, geologic mapping, and compositional similarities support the correlation of much of the upper Tesuque Fm east of the Rio Grande (particularly northeast of the San Juan Indian Reservation) to the lower and middle CFTS. This correlation, and the lack of significant sedimentologic differences between the CFTS and upper Tesuque Formation, raises significant concerns whether to retain the Charnita Formation as a member of the Tesuque Formation or abandon it altogether. In addition, suggest differentiating the Tesuque Formation into members using compositional and textural criteria; this would retain the current Chama-EI Rito, Ojo Caliente Sandstone, and Cejita Members. However, the Nambe, Skull Ridge, and Pojoaque Members are less lithologically distinct and difficult to differentiate south of Tesuque Pueblo and north of the Santa Cruz River. The Nambe, Skull Ridge, and Pojoaque Members each contain Lithosomes A and B; thus, differentiating this sediment using the lithosome approach of Cavazza (1986) would be more objective and more regionally applicable.