Neogene geology of the Isleta Reservation and vicinity, Albuquerque Basin, central New Mexico

Maldonado, F., Connell, S. D., Love, D. W., Grauch, V. J. S., Slate, J. L., McIntosh, W. C., Jackson, P. B., and Byers, F. M., Jr., 1999, New Mexico Geological Society, 50th Field Conference Guidebook, p. 175-188.

ABSTRACT

Geologic mapping of the Isleta Reservation and contiguous areas, Bernalillo, Valencia, and western Torrance Counties, New Mexico, has revised our understanding of the stratigraphy, structure, and geomorphic evolution of the Albuquerque Basin. This paper summarizes studies of the Neogene-Quaternary Santa Fe Group and younger deposits, rift-related geologic structures, and geomorphology. We divide exposures of the Santa Fe Group into three major facies: a western-margin facies derived from major tributary fluvial systems (ancestral Rio Puerco) draining the adjacent Colorado Plateau and Sierra Nacimiento: a central facies containing deposits of the ancestral Rio Grande axial-fluvial system; and an eastern-margin facies derived from the adjacent rift-border uplifts of the southern Sandia, Manzanita and Manzano Mountains. Geologic mapping, stratigraphic studies, and radioisotopic data for underlying Santa Fe Group deposits indicate that the aggradational top of the group as defined by geomorphic surfaces is diachronous. The oldest geomorphic surfaces are the Pliocene and Plio-Pleistocene Cañada Colorada and Llano de Albuquerque, respectively. The youngest surface is the early Pleistocene Sunport surface. The Llano de Manzano is a post-Santa Fe Group geomorphic surface formed on younger eastern-margin piedmont deposits. Dominantly north-trending faults crosscut older northwest-trending faults that segmented the Santa Fe Group into multiple sub-basins. The western basin margin is characterized by numerous normal faults with generally down-to-the-east movement; several shorter down-to-the west faults are antithetic to the dominant western margin faults and form local horsts and grabens. The eastern margin is defined by numerous generally down-to-the-west normal faults. The dominant eastern-margin faults are the range-bounding faults of the Manzanita and Manzano Mountains and Hubbell Spring fault zone. The Hubbell Spring fault zone is a major intrabasinal structure, about 5-8 km west of the eastern-margin faults that juxtaposes Permo-Triassic rocks against eastern-margin and central-basin facies. The results of this study do not support the presence of a discrete southwest-trending Tijeras accommodation zone of Neogene age as proposed by Russell and Snelson (1994). Mapping, aeromagnetic, gravity, and subsurface data demonstrate that the Tijeras fault zone joins the Hubbell Spring and southern Sandia fault zones just south of the Four Hills, and is not expressed southwestward across the basin. Results of this study do not support the presence of the north-trending Rio Grande fault of Russell and Snelson (1994). Instead, we interpret an older (late Oligocene-Miocene) northwest-trending structure that we call the Mountainview fault zone between the southwestern margin of the northwest-trending Mountainview prong and the Isleta Pueblo graben, a northwest-trending, fault-bounded depression. The northwest-trending prong and depression were subsequently cut by younger, generally north-trending faults as the Albuquerque Basin widened during late(?) Miocene and Pliocene time.