Geochronology and geochemical analysis of Quaternary travertine deposits at the Belen quarries of Mesa Aparejo, NM: Evaluation of travertine facies for paleohydrology and paleoenvironment Studies
— Alexandra Priewisch, Laura J. Crossey, Karl E. Karlstrom, Hank S. Chafetz, and M.A. Cook

The depositional facies and stable isotopic composition of a large-volume Quaternary travertine deposit located in the Rio Grande rift in New Mexico provide a record of the paleohydrology of springs along the western Rio Grande rift flank. Our results show that lateral and vertical facies variations within a travertine deposit developed due to changing depositional environments, which are primarily related to the formation of travertine mounds sourced by springs along the rift-bounding Comanche and Santa Fe faults. Important travertine facies are 1) a terraced mound and sloping fan facies that represents surface flow, and 2) a vein facies that reflects artesian waters within the developing mounds. Stable oxygen and carbon isotope analyses of the two facies show similar δ¹⁸O and δ¹³C values, ranging between -6.6‰ and -9.3‰, and +1.3‰ and +6.1‰, respectively. The range of δ¹⁸O values is similar to nearby springs along the west side of the rift and is interpreted to reflect variable mixing of endogenic (deeply derived) spring discharge with meteoric water. The δ¹³C values are significantly higher than values of nearby springs (δ¹³C = -1 to -8) and are interpreted to be controlled by variable CO² degassing rates. The age and volume of the travertine deposit suggests that the mounds archive an estimated minimum of 54 Gigatons CO² that degassed over a period of 456 ka along the fault system. Significant additional amounts of CO² likely escaped to the atmosphere during travertine formation and δ¹³C fractionation. Travertine mound growth was facilitated by times of high CO² flux and times of high groundwater head in confined aquifer systems.