INTEGRATED GEOLOGIC FRAMEWORK STUDIES IN THE ESPAÑOLA BASIN, RIO GRANDE RIFT, NORTH-CENTRAL NEW MEXICO

Geologic mapping closely integrated with geophysical surveys and topical studies of stratigraphy and structure are providing better understanding of the evolution and three-dimensional form of the Española basin of New Mexico. The Española basin, with an overall form of a west-dipping half graben, is one of a series of right-stepping basins that make up the Rio Grande rift. Geologic maps at 1:24,000 scale have been completed for most of the basin by the NMBGMR and the USGS. Neogene sediments derived from multiple source areas fill the basin and include aquifer facies that provide important municipal water supplies for Santa Fe and other communities in the basin. The age and deposition rates of basin-fill sediments are constrained by tephrochronology. Paleomagnetism and ⁴⁰Ar/³⁹Ar geochronology studies refine the internal stratigraphy and age of the Pliocene-Quaternary Cerros del Rio volcanic field that interfingers with late-stage sediments in the southwestern part of the basin. The general west dip of basin strata is interrupted by several intrabasin faults; studies of faults both within and at the margins of the basin establish their geometry, kinematics, geochemistry, and role as hydrogeologic features. High-resolution aeromagnetic surveys are used to identify and extend intrabasin faults, sense buried volcanic rocks, and provide depth estimates to basin floor. Gravity and electromagnetic surveys further constrain the basin geometry and internal physical properties. Data from these diverse studies, and from sparse deep drillholes, are being implemented in three-dimensional geologic modeling to visualize and better understand the form of the Española basin as a geologic framework for hydrogeological concerns. The Española basin shallows sharply south of Santa Fe, restricting the thickness of basin-fill aquifers. This basin form may reflect a relay ramp that transfers extension west to the adjacent Santo Domingo basin, consistent with paleomagnetic evidence of modest counterclockwise rotation of the southwestern part of the basin.