SUBSURFACE STRATIGRAPHY OF THE SANTA FE GROUP NEAR ALBUQUERQUE, NEW MEXICO, USING GROUNDWATER MONITORING WELL DATA

Numerous nested piezometers were recently completed to depths of <500 m in the upper Santa Fe Group near Albuquerque. Geologic mapping, examination of cuttings, and borehole geophysics for these and neighboring wells were used to differentiate subsurface facies and textural trends in the Albuquerque area. Offset of marker zones between wells also helps constrain buried fault locations. The Sierra Ladrones Fm contains axial-fluvial deposits of the ancestral Rio Grande (ARG), and basin-margin deposits derived from the Sandia and Manzano Mts. The Arroyo Ojito Fm contains deposits of the ancestral Rio Puerco/Rio San Jose fluvial systems, which drained the western border of the basin. In northern Rio Rancho, wells commonly bottom in upper Zia Fm sand and sandstone.

The Arroyo Ojito Fm is mostly reddish-brown (7.5YR) muddy sand and gravel, containing subangular volcanic, rounded quartzite, angular red granite, and sparse chert clasts. ARG deposits extend to within 3-4 km of the Sandia Mountains; they consist of yellowish-brown (10YR) sand, gravel, and minor mud, containing subrounded volcanic, quartzite and granite clasts. Fluvial facies are generally more heterolithic than the reddish-yellow (7.5YR) locally derived basin-margin facies, which contain angular pink granite with minor schist, white quartz and sparse rounded limestone clasts.

Three major textural intervals or zones are recognized within the fluvial facies: 1) a lower muddy sand; 2) a middle sand, gravel and mud; and 3) an upper gravel and sand. The lower fine-grained zone is commonly encountered near the base of wells. Middle and upper zones tend to thicken eastward from ~75 m along the Ceja del Rio Puerco to >270 m beneath NE Albuquerque. The middle interval is typically dominated by upward-fining sequences of sand and sandy mud and tends to coarsen and grade upward into the upper interval. South of Los Lunas, the upper gravel and sand interval thins to <40 m and the middle sandy zone is thicker.