New Mexico Geological Society Annual Spring Meeting — Abstracts

The course, geometry, and length of fluvial systems results from the competing processes of surface uplift (tectonic, isostatic, or dynamic), surface weathering (climate, vegetation, rock strength), and efficiency of sediment transport (climate, surface gradient). These factors in turn impact the location and evolution of adjacent sedimentary basins (Romans et al., 2016). The Eocene fluvio-lacustrine Baca Formation is critical to understanding sediment transport in central New Mexico at the end of Laramide deformation. 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. Mapping and clast composition have been interpreted to suggest that water and sediment from the Baca Basin intermittently spilled eastward across the Sierra Uplift and flowed south through the Carthage-La Joya Basin, resulting in deposition of the Baca Formation strata in the Carthage-La Joya Basin (Cather, 2009). However, substantial differences in strata found in each basin and the appearance of down-stream increase in clast size calls this interpretation into question.

The potential for sedimentary connection between the Baca and Carthage-La Joya Basins is assessed using U-Pb detrital zircon geochronology on nine new, and two existing (Donahue, 2016) samples. These data are compared visually with age-distribution kernel density estimates and numerically using cross-correlation. Seven of the samples analyzed in this study and the previously published data suggest that the Baca and Carthage-La Joya Basins did share a sedimentary source. These data are also compared to data published in the San Juan, El Rito, Galisteo, and Tornillo Basins. Of these basins, the Galisteo Basin is the only basin to suggest a potential common sedimentary source. Two of the samples analyzed in this study have substantially different age spectra than the other seven Baca Formation samples. One is interpreted to represent a deposit from a small tributary catchment that had not been mixed with trunk-stream sediment. The other is interpreted to be mismapped and part of the lower Spears Group, the unit overlying the Baca Formation.

Our statistical methods suggest that sedimentary connections throughout central New Mexico may be more complex than previously thought. We suggest that drainage through the Galisteo Basin did connect in some way to the Baca and Carthage-La Joya Basins. However, this conclusion does not preclude the possibility that an axial river flowed east out of the Baca Basin into the Carthage-La Joya Basin.

References:

1. Cather, S. M. Stratigraphy and structure of the Laramide Carthage–La Joya Basin, central New Mexico. New Mexico Geological Society Guidebook 60, 227–234 (2009).
2. Donahue, M. M. Episodic uplift of the Rocky Mountains: evidence from U-Pb detrital zircon geochronology and low-temperature thermochronology with a chapter on using mobile technology for geoscience education. (University of New Mexico, 2016).
3. Romans, B. W., Castelltort, S., Covault, J. A., Fildani, A. & Walsh, J. P. Environmental signal propagation in sedimentary systems across timescales. Earth-Science Reviews 153, 7–29 (2016).