GEOLOGIC MAP AND CROSS SECTIONS OF THE SOUTHERN ESPAÑOLA BASIN

We present a geologic map of the southern Española Basin, in the vicinity of Santa Fe, New Mexico (Open-file Report 531; N.M. Bureau of Geology and Mineral Resources). In this semi-arid region, knowledge of subsurface extents and depths of aquifers is critical for groundwater management. This map extends from the Rio Grande eastward to the Sangre de Cristo Mountains, and from Pojoaque southward to just north of Galisteo.

Eight cross sections illustrate the stratigraphy and structure of the southern Española Basin. Most of the >30-8 Ma basin fill belongs to the Tesuque Fm of the Santa Fe Group, which is subdivided into lithofacies assemblages that correspond to paleogeographic position during basin aggradation: western alluvial slope, basin-floor, eastern alluvial slope and fans, and ancestral Santa Fe River deposits. A coarser-grained Plio-Pleistocene unit, the Ancha Fm, unconformably overlies the Tesuque Fm. The structure of the basin north of Interstate 25 corresponds to a west-tilted half-graben called the Cañada Ancha graben. The master fault of this half-graben is inferred to lie under the eastern Caja del Rio plateau, based on geophysical modeling of gravity and seismic data by Tien Grauch et al. (U.S.G.S. Prof. Paper 1761). The base of the Santa Fe Group in the deepest part of this graben is as much as 700 m below sea level. The graben is bounded on the east by a west-down flexure called the Barrancos monocline and on the south by the Rancho Viejo hinge zone. South of Interstate 25, the southern Española Basin is a structural platform that has been slightly folded into a north-plunging syncline.

The geologic map utilizes a GIS geodatabase schema that allows for detailed attribution of geologic units, structures, and contacts as well as feature-level metadata (see http://geoinfo.nmt.edu/statemap/datamodel). Attributes for lithologic contacts and faults include the interpretative basis, scientific confidence, degree of exposure, and data source. These attributes are critical for assessing controversial buried faults and their potential hydro-geologic impacts. Comprehensive feature attribution and a very granular geodatabase schema will allow GIS users to analyze and display the data in novel ways and should facilitate integration with other rapidly evolving geoscience datasets in the Española Basin.