Hydro-geologic Framework of the Binational Western Hueco Bolson-Paso del Norte Area, Texas, New Mexico, and Chihuahua: Overview and Progress Report on Digital-Model Development

The binational western Hueco Bolson-Paso del Norte area of the southern Rio Grande rift (RGr) tectonic province occupies parts of Trans-Pecos Texas and south-central New Mexico, USA, and north-central Chihuahua, MX. It includes a long reach of the Rio Grande Valley, adjacent parts of the southern Mesilla and Tularosa Basins, and the El Paso-Ciudad Juárez metro-area with a population of about two million. This overview and progress report emphasizes recent development of hydrogeologic-framework models and GIS datasets that integrate large amounts of geologic and geochemical information on Neogene RGr basin-fill (Santa Fe Group) and river-valley aquifer systems. The digital GIS format (ESRI ArcGIS©) allows 3-D integration of surface and subsurface information that can be used in numerical groundwater-flow modeling and hydrogeochemical interpretations. Provisional hydrogeologic maps and cross sections completed to date include a surficial map, 11 sections (to mean sea level), and a structure-contour map of the base of the basin-fill aquifer system in the Paso del Norte area. The hydrogeologic framework of basin-fill aquifers is defined in terms of 1) dominant lithofacies-assemblages (LFAs) that are grouped as informal hydrostratigraphic units (HSUs) and 2) basin-boundary and intra-basin structural controls.

Late Cenozoic extensional-tectonic features that characterize the entire RGr region have had a profound influence on both basin-fill composition and groundwater flow and chemistry. Primary tectonic components are half-graben basins and flanking ranges that are linked across zones of structural accommodation. Major aquifers comprise coarser-grained LFAs deposited by 1) ancestral-river distributaries in Pliocene to Early Pleistocene time and 2) the Late Quaternary fluvial-channel system that occupies the present inner (El Paso/Juárez) valley of the Rio Grande. These poorly consolidated sediments are also grouped into informal upper to middle Santa Fe basin-fill and river-valley HSUs. Aquifer horizontal hydraulic conductivities commonly range from 3-30 m/day, and saturated basin-fill fluvial sequences are as much as 300 m thick and 30 km wide. In marked contrast, inset river-valley fills are less than 30 m thick and 9 km wide. Except for deeply buried eolian-sand facies, subjacent middle to lower Santa Fe basin-floor deposits (Miocene) and intertonguing piedmont-slope LFAs have much lower aquifer potential because of finer matrix and more consolidation and cementation.

This report comprises four major sections followed by “Concluding Remarks” and a comprehensive list of more than 165 cited references. The Introduction (Part 1) covers the purpose and scope of the study, the location and physiographic setting of the Hueco Bolson region, and a summary of research methods and major data sources. Relevant conceptual hydrogeologic models are described in Part 2, with emphasis on 1) geohydro-logic systems in the Basin and Range province and 2) basic hydrogeologic-model concepts. Part 3 covers the hydrogeologic setting of the Hueco Bolson-Paso del Norte area, first from a general structural-geologic perspective and then with emphasis on the hydrogeologic map and cross-sections. Late Cenozoic evolution of the Hueco Bolson aquifer system and inferences on hydrogeologic controls on groundwater flow and geochemistry are emphasized in Part 4.