Geochemistry and microbial diversity of CO2-rich springs and U-series dating of travertine from the Tierra Amarilla anticline, New Mexico
— Brandi Cron, Laura J. Crossey, Karl E. Karlstrom, Victor J. Polyak, Asmerom, Yemane, and Chris McGibbon, [eds.]

Abstract:

Abstract—This paper explores the water geochemistry, microbial heterogeneity, and paleohydrological longevity of a set of desert springs in north-central New Mexico. This series of CO2-rich springs is aligned along a southern extension of the Nacimiento fault at the Tierra Amarilla anticline in the boundary zone between the Colorado Plateau and Rio Grande rift. The springs are warm (24±1°C) year around and sustained by artesian head. Geochemical data show 3
He/4 He ratios of 0.17–0.20 RA, which indicates the presence of mantle-derived helium in the groundwater. Carbon isotope values range from -4.6 to -8.1 per mil, and water chemistry modeling of eight samples indicates that most of the CO2 is endogenic and derived from deep (magmatic) sources (Cendo = 89%); the rest of the CO2 is from dissolution of carbonate in the aquifer (Ccarb = ~6%) and from organic sources such as soil gas (Corg = ~5%). Stable isotopes of the water plot to the right of the Global Meteoric Water Line, suggesting geothermal influence from the Valles Caldera. The combination of new water chemistry and spring monitoring reported here illustrates the unique character of these carbonic, travertine-depositing warm springs. These high-CO2, low-dissolved
oxygen (DO) waters host unique microbial ecosystems. DNA and 454-sequencing analyses revealed native microbiological communities including Zetaproteobacteria. The Zetaproteobacteria had previously only been known from submarine seamount communities, such that the Tierra Amarilla springs host the first published occurrence of chemolithotrophic iron-oxidizing Zetaproteobacteria in a continental setting. These communities are interpreted to be structured to inhabit ambient-temperature terrestrial springs via metabolic processes similar to chemolithotrophic communities found in deep-sea vents with inferred metabolic reactions including oxidation of hydrogen, manganese, and hydrogen sulfide. We report 17 new U-series dates from travertine deposited by the springs to evaluate the longevity of the Tierra Amarilla spring system. Highest-elevation extinct mounds give ages from 269 to 212 ka; lower mound systems range in age from 105 to 70 ka; youngest travertines return ages from 9 ka to 630 years. Travertine mound springs north of Highway 550 are actively cementing Rio Salado gravels in the modern floodplain and provide an analog for travertine cements and caps on Rio Salado terrace gravels that extend ~200 m
up the dip slope of the southern nose of the Nacimiento Mountains. These terrace travertines range in age from 534 to 31 ka and provide a good incision record for the Rio Salado. The data presented in this paper show artesian spring alignment along a southern continuation of the Nacimiento fault, multi-year-consistent water temperature and conductance (lack of seasonality), deep sources for the high CO2 and He, unique chemolithoautotrophic microbiology, and >500 ka longevity of the spring system as recorded by travertine. These findings are consistent with models for geothermal influences from the Valles Caldera, neotectonically active southern Nacimiento Mountains fault systems, and episodicity in deposition of travertine that may be facilitated during wetter climate intervals.


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Recommended Citation:

  1. Cron, Brandi; Crossey, Laura J.; Karlstrom, Karl E.; Polyak, Victor J.; Asmerom; Yemane; McGibbon, Chris, 2024, Geochemistry and microbial diversity of CO2-rich springs and U-series dating of travertine from the Tierra Amarilla anticline, New Mexico, in: New Mexico Geological Society, Guidebook, 74th Field Conference, Karlstrom, Karl E.;Koning, Daniel J.;Lucas, Spencer G.;Iverson, Nels A.;Crumpler, Larry S.;Aubele, Jayne C.;Blake, Johanna M.;Goff, Fraser;Kelley, Shari A., New Mexico Geological Society, Guidebook, 74th Field Conference, pp. 225-235. https://doi.org/10.56577/FFC-74.225

[see guidebook]