New Mexico Geological Society Annual Spring Meeting — Abstracts

Interpretation of borehole geophysical logs obtained from wells in the Albuquerque metropolitan area (AMA) of central New Mexico reveal laterally consistent stratigraphic patterns that provide a basis for local differentiation of the Santa Fe Group, the principal aquifer for communities along the Rio Grande Valley. Surface geologic mapping yields important clues to the distribution of faults and alluvial aquifer units in the region; however, Quaternary alluvium obscures numerous geologic structures. Integration of geologic mapping with borehole geophysical logs, well completion reports, driller's logs, and descriptions of cuttings from wells has significantly improved our ability to delineate structural features and depositional patterns that have an important bearing on the hydrology of the basin-fill aquifer system.

Two laterally extensive sequences of fine-grained silty sand and clay, provisionally named the Atrisco member of the Middle red formation, can be traced for several kilometers under the AMA (Allen et aI., 1998; Connell et aI., 1998). The top of the Atrisco member separates highly conductive, coarse-grained sand and gravel of the Sierra Ladrones Formation from underlying fine-to medium-grained silty sand and clay of the less conductive Middle red formation. The eastern basin margin is marked by a series of north-striking, down-to-the-west normal faults, such as the Sandia fault zone. The East Heights fault zone generally marks the eastern limit of highly conductive deposits of the Sierra Ladrones Formation. Syndepositional faulting is recognized by eastward thickening of Sierra Ladrones strata and local divergence of marker beds. Faulting along the eastern basin margin resulted in the accumulation of a relatively thick pile of fluvial sand and gravel beneath much of Albuquerque during Plio-Pleistocene time.