STRATIGRAPHY AND PROVENANCE OF THE BACA FORMATION IN THE BACA AND CARTHAGE-LA JOYA BASINS, CENTRAL NEW MEXICO

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 surrounding 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 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 documented throughout the Carthage- La Joya Basin suggests that, in contrast to published provenance models, the Baca Basin did not drain southeast through the Carthage-La Joya Basin. New geochronologic data from the Baca and Carthage-La Joya basins provides insight into the provenance of both basins to better understand their relationship within regional laramide drainage systems.