New Mexico Geological Society Annual Spring Meeting — Abstracts

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The Eocene fluvial-lacustrine Baca Formation is critical to understanding late Laramide sediment transport in central New Mexico. Here, we present new data to evaluate conflicting hypotheses about the connection between the Baca and Carthage-La Joya basins (e.g. Cather, 2009; Lucas and Williamson, 1993), as well as their connection to other Laramide basins. This study combines sedimentologic field techniques (e.g., measured section, imbrication/paleoflow measurements) with sandstone petrographic analysis and U-Pb detrital zircon (DZ) geochronology. Geochronologic analysis compares published data from the San Juan and Tornillo Basins to published data from the Baca and Carthage-La Joya basins. Our data suggests that the Baca and Carthage-La Joya Basins preserve two distinct fluvial systems.

The lithologies of strata mapped as Baca Formation differ substantially between the Baca basin in western New Mexico and the Carthage-La Joya basin in central New Mexico. Baca Basin strata comprise siltstones to medium-grained sandstones, whereas Carthage-La Joya strata are dominated by pebble to boulder conglomerates and minor fine- to coarse-grained sandstones. Published paleocurrent measurements from the Carthage-La Joya basin suggest southeastward paleoflow, whereas new data indicate northwestward paleoflow. This northwest paleoflow found throughout the Carthage- La Joya Basin suggests that the Baca Basin did not drain southeast through the Carthage-La Joya Basin (fig. 1). Limited published U-Pb DZ geochronologic data suggests similar sedimentary provenance in both basins; however, there is not yet enough data in the Baca and Carthage-La Joya Basins to draw meaningful conclusions.

References:

1. Cather, S. M., 2004, Laramide orogeny in central and northern New Mexico and southern Colorado: New Mexico GeologicalSociety Special Publication 11, 203–248 .
2. Cather, S. M., 2009, Stratigraphy and structure of the Laramide Carthage–La Joya Basin, central New Mexico: New Mexico Geological Society Guidebook 60, 227–234.
3. Lucas, S. G. & Williamson, T. E., 1993, Eocene vertebrates and late Laramide stratigraphy of New Mexico: New Mexico Museum of Natural History and Science Bulletin 2 145–158.