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New Mexico STATEMAP—Summary of Results

During the first seven years of STATEMAP, the New Mexico Bureau of Geology and Mineral Resources will have completed forty 7.5-minute quadrangles along the Rio Grande watershed. Each of the quads has added to our knowledge of various aspects of the environmental geology, hydrogeology, structural geology, engineering geology, Quaternary geology, and volcanic geology of New Mexico. Below is a brief summary of selected highlights from some of our map areas.

The greater Albuquerque area—Alameda, Bernalillo, Albuquerque East, Albuquerque West, Hubbell Springs, Isleta, Placitas, and Sky Village SE, 7.5-minute quads

The primary contribution of the STATEMAP project to studies of the Albuquerque Basin watershed is the establishment of a modern geologic framework for the rift-basin fill and flanking uplifts. This framework can be used to better understand the hydrogeologic (subsurface) character and geologic hazards of the basin.

A 1:50,000 geologic map of the Albuquerque metropolitan area was produced in 2008 by Sean Connell (no longer with the bureau). The map is a compilation of twelve 7.5-minute quads, eight of which are STATEMAP quads. This map is a critical foundation for the subsurface geologic model and ground water model being generated by the USGS.

Integration of new surface mapping with regional geophysical (magnetic and gravity) surveys and borehole data (lithology and geophysics) have refined previous studies of intrabasinal faults. Recent quad mapping has revealed much about subsurface fault geometries. Delineation of Santa Fe Group (upper-middle), piedmont and fluvial deposits have resulted in a better understanding of the distribution of facies within aquifer units and refined elements of the USGS regional groundwater-flow model of the basin. Mapping and integration of published and unpublished geochronologic and paleontologic data constrain the terminus of Santa Fe Group deposition under Albuquerque to the early Pleistocene, rather than middle Pleistocene as previously thought (Machette, 1985). Hydraulic data from municipal water-supply wells also correlate with surface and subcrop mapping of Santa Fe Group lithofacies (Connell et al., 1998ab).

Geologic mapping of post-Santa Fe Group deposits has resulted in a preliminary delineation of earthquake and geotechnical hazards. Incorporation of sedimentologic and geomorphic criteria for latest Pleistocene and Holocene deposits delineate areas that may be susceptible to consolidation of soils upon wetting (Cather and others, 1995; Connell, 1997). Damage to foundations built on hydrocompactive soils can be mitigated during construction; however, failure to recognize this condition has resulted in considerable damage and cost to property owners in the region.

Northern Albuquerque Basin

The northwestern portion of the Albuquerque 1:100K and southwestern portion of the Los Alamos 1:100,000 has seen a great deal of STATEMAP and EDMAP activity over the past four years. Mapping in a series of adjacent quadrangles, starting with the Ojito Springs quadrangle in the west, and continuing through the San Ysidro, Sky Village NE (Cerro Conejo), Jemez Pueblo, and Loma Creston quads has revealed important structural, stratigraphic, and sedimentologic features astride the northwestern shoulder of the Albuquerque basin. Faults strike predominantly north-south and northeast-southwest.

The former population is coincident with, if not reactivated, Laramide structures. The latter population parallels the Jemez lineament. Both fault populations commonly display a reversal of slip polarity along strike. Slip on a given fault system changes polarity at a segment boundary which is defined by a broad (~100-500 m) zone of stratigraphic offset where slip is partitioned along several high-angle faults that collectively define the fault tips of the overlapping segments. Faults are marked by both clay-rich gouge zones that are typically erodible and recessed in their topographic expression, and carbonate-rich cemented zones that are resistant and high-standing in topographic expression. The transition from gouge zones to cemented zones occurs along strike and may be related to the dominant grain size in the fault zone as suggested by ongoing studies at New Mexico Tech of the Sand Hill fault.

Exposures of the Santa Fe Group basin fill across the mapped quads is outstanding and has served as a type locality for the re-definition of Albuquerque Basin Neogene stratigraphy. In particular, the exposures in the Sky Village NE quadrangle along La Ceja escarpment have played a pivotal role in the re-definition of the Santa Fe Group (Connell et al., 1999; Tedford and Barghorn; NMGS 50th Guidebook). Santa Fe Group stratigraphy records: 1) filling of a broad, slowly subsiding rift shoulder ~20 - 15 Ma that filled with a predominantly eolian deposits; 2) a more rapidly subsiding rift shoulder ~15-8 Ma that filled with coarser-grained, reworked Abiquiu Fm and older Early Cenozoic and Mesozoic rocks derived from the Sierra Nacimiento and Colorado Plateau via the ancestral Rio Puerco; and 3) a hinged rift shoulder 8-0 Ma that filled with increasingly coarse and volcaniclastic rich-detritus sourced from the Jemez Mountains and Colorado Plateau. Full integration of the Rio Grande axial system sometime in the Pliocene and subsequent incision in the Pleistocene has exposed the Neogene stratigraphy and isolated any further deposition to that which has occurred locally as colluvial, alluvial, and eolian fills against tectonically produced fault scarps.

The most important stratigraphic finding was the delineation of ancestral Rio Grande gravel and sand, which serve as the principal aquifer in the Albuquerque Basin, over wider lateral and vertical extents than previously recognized. Along with better descriptions of piedmont facies, the new mapping of axial deposits will permit significant modifications (e.g., order of magnitude upward revisions of hydraulic conductivity) in the USGS groundwater model for this part of the Albuquerque hydrological basin. Intrabasin faults, some with 100–200 m of Quaternary displacement, have been mapped across two quadrangles and linked northward to major Neogene structures mapped in reconnaissance within the Jemez Mountains volcanic field. The faults likely partition the aquifer, as well, to account for a trough in the potentiometric surface west of, and at a lower elevation than, the Rio Grande. The geological maps are being integrated with ground-based and airborne geophysical data collected by USGS personnel, in order to produce a three-dimensional structural and stratigraphic assessment of the Cochiti Pueblo lands on these two quadrangles.

The most important applied results that has come out of these studies are that: 1) several mapped faults clearly offset Quaternary deposits, and are thus probably best classified as seismogenic; and 2) the redefined Santa Fe Group stratigraphy provides a consistent and reproducible foundation upon which to understand the hydrostratigraphic characteristic of these rocks which are deeply buried and constitute the aquifers for Rio Rancho and Albuquerque.

We have released a pair of adjacent 7.5' minute quadrangles in the northern Albuquerque basin as a single 1:24,000 map sheet, with explanation. The quadrangles, Santo Domingo Pueblo and Santo Domingo Pueblo SW, are located in the Santo Domingo basin, part of a complicated accommodation zone within the rift. The map illustrates upper Miocene through Quaternary basin-fill sediment, terrace deposits, and volcanic rocks along with intra-rift fault zones. The unique juxtaposition of the two quadrangles on a single sheet enhances visualization of stratigraphy and structure across nearly the entire width of the Santo Domingo basin. The map highlights the distribution of gravel-dominated parts of the regional aquifer, previously poorly known in this area, and is being utilized in the construction of new groundwater-flow simulations for the greater Albuquerque area. The mapping was done by Gary Smith and Andrika Kuhle, of the University of New Mexico in cooperation with Cochiti and Santo Domingo Pueblos. The two quadrangles, drafted separately, were seamlessly merged using Macromedia Freehand, and are color plotted on-demand on an HP-3500. This is the first such "double" geologic quadrangle map produced in New Mexico's Digital Geologic Map series, but its obvious advantages (lower printing cost, enhanced usefulness, longer cross sections) guarantee that we will merge other pairs of maps where appropriate.

Placitas development area hydrogeologic study

Geologic mapping of the Placitas and Bernalillo 7.5-minute quads has provided an essential geologic framework for a county-funded NMBGMR hydrogeologic study of the Placitas development area. The Placitas area, a rapidly growing community at the northern end of the Sandia Mountains, overlaps these two quads and lies within a structurally complex rift-margin step between the Santo Domingo and northern Albuquerque sub-basins. Findings of this ground-water study show that faults and stratigraphic boundaries have compartmentalized the pre-Tertiary bedrock aquifers. The upper Santa Fe Group basin fill aquifer consists of six major hydrostratigraphic units which reflect the major facies and lithologic units dissected into fault-bounded blocks and benches. Recharge, water quality, and ground-water residence times are spatially variable and dependent on various geologic controls. By combining detailed geologic, hydrologic, and hydrogeochemical data at a scale of 1:12,000 in GIS format, this study has achieved the necessary spatial control of complex data sets required to clearly delineate the locations of aquifers, aquitards, hydrologic boundaries and preferential ground-water flow pathways. Both the geologic and ground-water mapping products can be used to support land use decisions in the rapidly developing area.

East Mountain area and Estancia Basin—Sandia Park, Tijeras, Sandia Crest, Sedillo, San Pedro, and Edgewood quadrangles

Residential development is rapid along the east side of the Sandia and Manzano Mountains. Many houses use septic tanks and private water wells. Large volumes of groundwater are being pumped in the adjacent Estancia Basin in order to support development in the East Mountain area, and to maintain traditional agricultural activities in the basin. Water levels in the main pumping centers in the Estancia Basin have dropped historically by about 60 ft, and preliminary groundwater-modeling results indicate that an additional 60 ft of drawdown will occur over the next few decades. Projected groundwater depletions would essentially de-water the valley-fill aquifer system in much of the Estancia Basin. Administration of water rights in the Estancia Basin is contingent on accurate information about the hydrogeology of the area and realistically constrained numerical models of groundwater flow systems. In addition, detailed geologic mapping is needed for site-specific hydrologic studies related to groundwater contamination and environmental issues.

Prior to recent mapping activities, information about the geology in the East Mountain area was generalized and ignored Quaternary deposits, which are important components of the landscape and groundwater flow systems in the area. The distribution of stratigraphic units and patterns of fractures within carbonate rocks of the Pennsylvanian Madera Group, which occur at the surface in groundwater recharge areas of the Estancia Basin, have also been poorly documented. Our maps in the East Mountain area provide new details concerning the hydrogeologic framework of this increasingly populated area. In addition to providing new information about the surface geology in the area, an effort has been made during recent mapping to compile information about the groundwater system, including the distribution of hydraulic head and the thickness of aquifers. Although this information is still in a preliminary form, continued efforts are expected to provide hydrologic data that will be useful to government and private planners.

A number of important scientific issues are also being addressed by the mapping efforts. For example, the Sandia Park quad contains the best exposures of the Tijeras fault system. In one locality, vertical strike-slip faults appear to offset Quaternary-age soil horizons. If so, this has profound implications to the relatively recent seismic history of the Albuquerque area. A follow-up project, funded by the USGS Earthquake Hazards Program, is now underway. Quaternary deposits along the eastern piedmont of the Sandia and Manzano Mountains have been virtually ignored in previous geologic mapping of the area. Recently completed and ongoing mapping activities are providing the first information about the distribution of surficial deposits in these areas, and will help to reconstruct the history of latest Tertiary and Quaternary landscape development in this transitional area between the Rio Grande rift and the High Plains.

Veguita quadrangle

Preliminary results from the Veguita quad suggest that recurrent movement on several faults exposed on the quadrangle, including the Sabinal fault zone, which is suspected of generating the swarm felt in Bernardo in 1991. Current mapping of the floodplain of the Rio Grande might be used in land use planning. Because New Mexico Tech hydrology and geology students mapped and got air permeameter results from basin-fill facies exposed in the quadrangle, we can infer much about basin geometry and likely ground water flow paths. New data on sediment cementation and orientations of concretions has helped constrain paleoflow patterns.

Ojo Hedionda quadrangle

This region comprises much of the "Galisteo Lowlands" and is underlain by a full section of Cretaceous formations from the Dakota Sandstone to the Mesaverde Group. Sedimentary strata of Triassic to Tertiary age exist on the east limb of the NNW-plunging syncline that defines the northern end of the Estancia Basin. The Oligocene(?) Cerro Pelon laccolith and the Creston dike extend into the quadrangle from the Ortiz igneous center approximately 8 miles to the west. The basal contact of the Paleocene(?) Diamond Tail Formation lies with angular unconformity across the Point Lookout Sandstone and underlying Niobrara Shale as a result of Laramide deformation. A large transfer fault system associated with the Rio Grande rift in the eastern portion of the quadrangle separates the Glorieta Mesa uplift from the Estancia basin.

Loma Creston quadrangle

This region is located on the SE margin of the Jemez volcanic field and the NW margin of the Albuquerque Basin. Both are major features of the Neogene Rio Grande rift. Geologic mapping and 40Ar/39Ar dating of volcanic strata in the quadrangle demonstrate rift-basin subsidence was contemporaneous with late Miocene volcanism in the Jemez field. Subsidence was controlled by north-trending, dip-slip, dominantly down-to-the-east, high-angle normal faults. South-facing relay ramps (downwarps) are common where north and south propagating faults were deflected by, or terminated in, pre-existing NE-trending basement shear zones. Miocene basin-fill units thicken eastward and southward across the longitudinal and transverse fault zones.

Volcanic strata record

Eolian sands and minor fluvial sands of the lower Santa Fe Group (Zia Fm) are older than 9.8 Ma. Volcanic-rich alluvial gravels of the middle Santa Fe Group (lower Arroyo Ojito Fm.?) were shed southward from growing andesitic/dacitic volcanoes at about 9 Ma. An easterly flowing granite/chert-rich fluvial fan system (upper Arroyo Ojito Fm (?) then overlapped and partly intertongued with the volcanic-rich alluvial gravels prior to 6.99 Ma. Strong subsidence then shifted east and southward; most of the volcanic-rich gravels of the Cochiti Formation (upper Santa Fe Group) accumulated in deep basins east of the Cocida-Oso fault zone and the southern segment of the Santa Ana fault zone. West of these faults, eroded remnants of the Cochiti Formation fill paleovalleys cut into older Santa Fe beds and volcanic units. Localized minor subsidence, faulting and sediment accumulation continued until about 2.44 Ma; since then the quadrangle has been deeply eroded by drainages tributary to the Rio Grande.

Socorro quadrangle

Major topographic features of the Socorro quadrangle include the west-tilted Socorro Peak block and west flank of the Socorro Basin; both are relatively young features of the central Rio Grande rift. The Socorro Basin is defined by dissected and faulted piedmont slopes that descend toward the Rio Grande at the east edge of the quadrangle.

Geologic mapping and 40Ar/39Ar dating of volcanic strata, in and adjacent to the quadrangle, have demonstrated the following major structural features and evolution.

Pliocene to Pleistocene sands and gravels of the ancestral Rio Grande form a major aquifer under the city of Socorro. Deep monitoring wells (e.g. 2,000 ft) will be needed to determine the maximum thickness and storage capacity of this important source of potable groundwater. Numerous late Quaternary fault scarps in the quadrangle (Socorro Canyon fault zone) demonstrate a significant seismic risk; however, earthquake recurrence intervals are presently not well constrained. Seismic risk may be increased by the presence of a geophysically defined mid-crustal magma body at 12 miles depth below the Socorro region. Numerous microearthquake clusters occur at depths of 6–7 miles below the Sedillo Hill area (9 miles SW of Socorro); this suggests the presence of slowly rising cupolas from the mid-crustal magma body. More work is warranted to evaluate the long-term probability of a volcanic eruption near Sedillo Hill and its potential impact to the Socorro area.

Golden, Captain Davis Mountain, and Madrid quadrangles

Mapping and compilation of the geology of the Golden, Captain Davis Mountain, and Madrid 7.5-minute quadrangles have revealed several important findings relating to the Tijeras-Canoncito Fault System (TCFS) and intrusive rocks of the Ortiz Porphyry Belt. The principal manifestation of the TCFS in the Ortiz Mountains is a graben filled with Eocene Diamond Tail Formation. About 3.5 miles of left-lateral stratigraphic separation is indicated across the TCFS on the Golden and Captain Davis Mountain quadrangles by an  offset of outcrops of the Dakota Formation. The Estancia Basin terminates against the TCFS in a north-northwest-plunging syncline and the southeast edge of the Espanola Basin abuts the TCFS on the Captain Davis Mountain quadrangle. The base of the Eocene Diamond Tail Formation lies on an angular unconformity on Mesa Verde Group sediments.

The Cerro Pelon laccolith, in the eastern portion of the Captain Davis Mountain quad was apparently fed from the Ortiz center. Cross-cutting relations with the mid-Tertiary intrusive rocks indicate that major movement on the TCFS occurred approximately at 30 Ma. Comparison of intrusive rocks from throughout the Ortiz Porphyry Belt (Cerrillos Hills, Ortiz Mountains, and San Pedro Mountains) shows a consistent picture of the igneous succession. Early andesite porphyry and, locally, rhyolite sills emanated from at least 4 laccolithic centers and inflated the entire Phanerozoic section. Later alkaline stocks and dikes are responsible for gold and base-metal mineralization throughout the Ortiz Porphyry Belt.

Summary of Apatite Fission-track Analysis, Sangre de Cristo Mountains, 1998-1999

Shari Kelley
Department of Earth and Environmental Science
New Mexico Tech
Socorro, NM 87801

This work is part of an ongoing STATEMAP project to analyze possible Neogene movement along major faults within the Santa Fe Range and Taos Range portions of the Sangre de Cristo Mountains using apatite fission-track thermochronology. A total of 29 samples were collected for analysis from the McClure Reservoir, Glorieta, Seton Village, Santa Fe, and Ranchos de Taos STATEMAP 7.5-minute quadrangles. The Borrego fault, a N-S trending fault that has a profound affect on the drainage patterns and topography in the Santa Fe Range, was the primary focus of last year's effort. Additional samples from the west side of the Santa Fe Range near Chupadero in the Tesuque quadrangle and from the Miranda graben area on the Rancho de Taos quadrangle were dated. Samples from Jicarita Peak and Santa Barbara campground were also collected to improve regional coverage.

Borrego fault

Samples were collected along three transects across the Borrego Fault: the traverses are, from south to north, Hyde Park, Pacheco Canyon, and Borrego Mesa. The Borrego fault changes character from south to north. At Hyde Park the Borrego fault is a wide (10s to ~100 m) zone of crushed rock with no discrete fault planes or kinematic indicators. At Pacheco Canyon, the granitoids within the fault zone are again shattered, but discrete N-S trending, west dipping planes (some with dip-slip slickenlines) are present. Finally, at Borrego Mesa/Rio Medio, the Borrego Fault is a relatively minor feature, causing some iron staining of the adjoining rocks. In one place, a gouge zone about 3 m wide was observed in the canyon bottom. The AFT ages on either side of the fault are 42 to 58 Ma at Hyde Park, 54 to 59 Ma at Pacheco Canyon and 53 to 61 Ma at Borrego Mesa. No notable difference in AFT age was observed across the fault, and there is no evidence for significant Neogene vertical offset based on the AFT thermochronology. One apatite fission-track age of ~36 Ma determined for a sample adjacent to a fault in the drainage west of the Borrego fault (Chamiza trail) may indicate Neogene vertical movement at this locality. Abundant planes recording oblique-slip motion characterize this fault.

Miranda Graben

Seven samples were collected across the Miranda graben south of Ranchos de Taos. Only four samples yielded apatite. AFT ages are 56±21 Ma (large error due to low uranium content) and 40 ± 4 Ma on either side of the Picuris-Pecos fault on the west side of the area. Samples Pennsylvanian sandstone from the east margin of the area are 86 ± 8 (due to unusual chemistry of the apatite) and 48± 4 Ma. The sampled structures do not seem to record Neogene vertical movement. The Miranda fault, a structure with unambiguous Neogene vertical motion, has not yet been sampled.

Other Areas

AFT ages from the Chupadero area on the Tesuque quadrangle are from 49 to 56 Ma, similar to AFT ages at low elevation on the Ski Hill Road on the Santa Fe quadrangle to the south (Kelley and Duncan, 1986).

The AFT ages from Jicarita Peak and Santa Barbara campground are 42 to 46 Ma.

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