Open-file Report - 539
Preliminary study of the geologic framework of the Colorado Plateau-Middle Rio Grande Basin transition, New Mexico.

Recent interest in the availability of deep groundwater resources along the structurally complicated transition between the Colorado Plateau and the Rio Grande rift in north-central New Mexico, resulted in the development of groundwater-flow models that suggested an impact on the Middle Rio Grande Basin (MRGB, also known as the Albuquerque Basin) from long-term pumping of wells that would exploit pre-Cenozoic aquifer units (Melis, 2009). Refinement of the regional conceptual geologic framework of the Colorado Plateau-MRGB transition was done in order to aid in the development of a revised groundwater-flow model of this region by Melis et al. (2011). The refined geologic framework was based on a compilation of previous stratigraphic work, an examination of data from 72 deep wells, and modifications to structure-contour maps of the base of the Upper Cretaceous Dakota Formation (Thaden and Zech, 1984) and the top of Proterozoic basement (Broadhead et al., 2009). The internal structure of the MRGB is dominated by subbasins and buried structural culminations that likely influence flows of deep groundwater. Structural control on the distribution of springs along the western flank of the MRGB is suggested by variations in basin-margin structure and stratal dips. Few springs are found along the highly faulted Laguna bench, whereas springs are common along the faulted eastern front of the Lucero uplift, where strata dip away from the MRGB boundary. Groundwater-flow across faults was examined by projecting juxtaposition seals and conduits across three fault zones that locally define the northwestern structural margin of the MRGB. A preliminary result of the fault juxtaposition analyses suggest discontinuous and discrete windows of groundwater flow along portions of basin-margin faults.

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