New Mexico Geological Society Annual Spring Meeting — Abstracts

Geological, geophysical, water quality, and aquifer testing data from 10-15 shallow (less than 500 ft total depth) and 6 deep (between 800 and 2000 ft total depth) wells or exploratory borings have been used to describe aquifer characteristics of fluvial facies alluvial aquifers within the Cieneguilla Member of the Tesuque Formation, and to provide preliminary aquifer data on the Ojo Caliente Member silty sand aquifer between 1000 and 1200 ft. These data also provide preliminary aquifer data on the Pennsylvanian Alamitos Formation aquifer underlying the basin fill sediments and delineate the location of the Upper, Middle, and Lower Servilleta Basalts (USB, MSB, and LSB) in the subsurface throughout the basin. lithologic data also provide some constraints on the thickness of basin fill sediments and on faulting both within the Rio Grande Rift and along the eastern Rift margin within the Taos Valley. Lithologic data from deep exploratory borings and wells are used to correlate the USB, MSB, and LSB from the Rio Grande eastward to EI Prado near the Sangre de Cristo mountain front (SCMF), where the flows either pinch out or are downdropped to depths greater than 500 ft below ground surface. Three, down-to-the-west faults are inferred from drill hole data between Blueberry Hill Road (Arroyo Seco) and Los Cordovas (USGS Gage #08276300). The Servilleta basalts pinch out south and east of the Taos Country Club (approximately 1.5 miles SE of Rio Pueblo de Taos and 2 miles SW of Rio Grande de Rancho). In the vicinity of the Town of Taos, the USB does not appear to extend as far east and south as do the MSB and LSB. Analysis of cuttings, geophysical logs, and drilling rates indicate that the MSB is often weathered and includes interbedded fluvial or alluvial fan sediments, whereas the LSB is a very hard, relatively non-fractured and non-weathered flow. In a south-north cross section from the Town of Taos 1996 exploratory boring (Town-expl.) located approximately two miles west of the SCMF and one mile south or Rio Fernando de Taos to the Taos Pueblo K-2 Karavas Tract well (K-2 well) located approximately 3 miles west of the SCMF and one-half mile north of Rio Pueblo de Taos, basin fill thickness varies from 720 feet in Town-expl. to greater than 2037 feet in the K-2 well (Sorrell and Banet, 1993, Karavas Tract Exploratory Well: Bureau of Indian Affairs report). The Town-expl. boring penetrated 300 ft of Paleozoic sandstone, limestone, and shale interpreted as the Pennsylvanian Alamitos Formation underlying the MSB, LSB and interbedded Cieneguilla Member, Tesuque Formation sediments. A buried fault between Townexpl. and the K-2 well offsets the Alamitos Formation a minimum of 1340 feet and exhibits down to the north displacement (vertical offset). The fault does not offset the MSB.

The Agua Azul aquifer is an axial fluvial sandy gravel aquifer located within the Cieneguilla Member below the USB and penetrated by several wells tested by the authors in the Taos valley. Transmissivity (T) calculated from 48-to 96-hour pumping tests range from 280 to 700 felday (hydraulic conductivity (k) ranges from B ft/day to 26 ft/day) , and storage coefficient (S) ranges from 2.5 x 10^-4 to 5.3 X 10^-4. Vertical hydraulic conductivity (k') through USB and interbedded clay was calculated from a single pumping test as 0.02 ft/day. Aquifer coefficients calculated from several pumping tests of wells completed in a shallow fluvial and alluvial fan sandy gravel aquifer overlying the USB exhibit a range in T from of 400 to 1200 ft²/day and a range in S from 1.0 x 10^-3 to 1.2 x 10^-2. Preliminary testing of the Ojo Caliente Member silty sand aquifer between 1000 and 1200 ft suggest that k is lower than in the shallow aquifers (e.g. a few feet/day), although a greater aquifer thickness may result in similar values for T. Water quality data indicate that the deep Ojo Caliente Formation aquifer may be high in fluoride and weakly alkaline. Water level measurements indicate that an upward gradient exists in deep aquifers whereas shallow aquifers exhibit a downward gradient and discharge to the Rio Grande (Sorrell and Banet, 1993).