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GRAUCH, V. J. S., U. S. Geological Survey, Denver, CO, RICHARD P. LOZINSKY, Fullerton College, Fullerton, CA, and G. R. KELLER, University of Texas at El Paso, El Paso, TX

ABSTRACT: Is There a Buried Paleozoic Basin Containing Significant Salt in Southeastern Albuquerque Basin, New Mexico?

Recent gravity studies show that the subsurface structure of the Albuquerque basin is more complex than previously thought. The Grober-Fuqua #1 oil exploration well in the southeastern part of the Albuquerque basin is the only deep well located in the southern part of an extensive, N-S elongated gravity low (20 mGal amplitude). Low-density Tertiary basin fill in the well rests on Triassic rocks at 1384 m depth, a fill thickness that is insufficient to explain the extensive gravity low. Identifications of lithologic units within the well are based on comparisons to sandstone petrology of cores and surface rocks from throughout the basin. Sandstone from the lower part of the Grober-Fuqua well is petrologically indistinguishable from Triassic sandstone mapped nearby and differs significantly from the sandstone petrology of Tertiary units.

Simple gravity-profile models were developed to test several explanations for the gravity low. Only one model fits both gravity and borehole evidence and is consistent with depths estimated for magnetic basement. Seismic data are not available for the area. The model depicts a buried, Triassic or Paleozoic basin containing up to 4 km of low-density rocks (2.38 g/cm3). This density, which is much lower than expected for units of these ages (average 2.55 g/cm3), can be reasonably explained only by the presence of low-density salt (2.0 g/cm3), as much as 30% salt by volume. From regional geologic considerations, salt is most likely to occur within the Permian section. The N-S elongation of the gravity low and its proximity to N-S elongated Pennsylvanian basins located to the south and east suggest basin development began in Pennsylvanian time.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico