A GEOLOGIC OUTLINE OF THE ALBUQUERQUE BASIN

The Albuquerque Basin of the Rio Grande rift was the subject of intensive multiagency geologic and hydrogeologic study beginning in the 1990s. A focus of geologic study was on new mapping to better describe and understand the Santa Fe Group basin-fill aquifer system, which currently provides much of the region’s supply of water. Results of these geologic studies led to the creation of a refined stratigraphy that incorporated subsurface data and improved age control. This work illustrated how the structural geometry and geomorphic evolution of this basin influenced the spatial distribution of rock types and faults and explained why parts of this basin possess more productive water-supply wells than others. The Albuquerque Basin is segmented into smaller complexly faulted half-graben sub-basins by strain accommodation zones. Rifting began in late Oligocene time with the creation of segmented, internally drained sub-basins that were dominated by fluviolacustrine and eolian sediments. By late Miocene time, sandier fluvially dominated extrabasinal sediments associated with the ancestral Rio Grande reached the northern part of the basin and ended in playa lakes at the southern end. By early Pliocene time, this axial river flowed through the basin and into southern New Mexico. By Plio-Pleistocene time, the axial-river load had coarsened and migrated towards the present position of the Rio Grande valley, where it incised to form a continuous river valley. In the Albuquerque-Rio Rancho area, the western basin-margin is structurally high and potable groundwater is mostly derived from consolidated and calcite-cemented Miocene sediments. This structurally high western flank also provides shallower targets for petroleum development in the subjacent Mesozoic strata. The structurally lower eastern part of the basin under Albuquerque contains younger, coarser, and thicker Plio-Pleistocene strata that produce some of the largest yields and generally higher quality groundwater in the region. An unconformity locally aids in differentiating between the less productive Miocene and more productive Plio-Pleistocene deposits. As potable water sources become scarce, abundant brackish-water resources may become attractive production targets for desalination along the structurally higher