Soils in the arid to semi-arid piedmont landscapes of central New Mexico were examined in order to evaluate surficial processes and landscape evolution in the central Rio Grande Rift. These soils were found to contain key information regarding pedologic and geomorphic responses to climate change, rifting and base level drop. A rare association of sepiolite and palygorskite occurs in old soils formed in eolian fines. Pedologic and mineralogical data indicate that palygorskite formed by transformation of dust-borne, aluminum-rich minerals, and that sepiolite subsequently formed by transformation of palygorskite. The association of these two minerals, and geomorphic observations, confirm the existence of a 1 – 3.5 Ma abandoned geomorphic surface of the ancestral Rio Grande. In contrast to Mormon Mesa, Nevada, and Ogallala Formation paleosols, massive cementation by pedogenic carbonate, and chaotic pedogenic carbonate pendants are notably absent in soils formed on the 1 – 3.5 Ma surface. It is hypothesized that abandonment of geomorphic surfaces, largely due to down-cutting by the ancestral Rio Grande, and slow accumulation of fine eolian sediments resulted in the absence of well-developed petrocalcic soil properties usually observed in soils of this age. Other geomorphic observations confirm the hypothesis of an ancestral Palo Duro drainage in the McKensie Flats Basin. In contrast to monogenetic soils, only one polygenetic soil demonstrates stable carbon isotope depth trends similar to the diffusion model of Cerling et al. (1989). Low delta 13C carbonate values in the near-surface reflect the introduction of exogenous material. Low delta 13C carbonate values at >50 cm of depth reflect buried rooting zones of plant assemblages that occurred in the past. An association between buried soil boundaries and shifts in delta 13C carbonate depth trends indicates that changes in C3 and C4 plant assemblages have occurred in the past. These shifts may reflect paleo-environmental conditions present when the soils formed, over-printing of Holocene paleo-environmental conditions onto older soils, or “time-averaged” combinations of both records.
Microtopography, soil grain size, induration, and surface clast cover potentially influence the distributions of Larrea tridentata, Bouteloua gracilis, and Bouteloua eriopoda. However, distributions of these species were not affected by lithology, soil age, soil salinity, or high soil pH.
Earth and Planetary Sciences
Level of Degree
Department of Earth and Planetary Sciences
First Committee Member (Chair)
Second Committee Member
Third Committee Member
Fourth Committee Member
This research was partially supported by an NSF grant to the University of New Mexico for Long-term Ecological Research, and by the US Fish and Wildlife Service, Sevilleta National Wildlife Refuge, and Los Alamos National Laboratory (LA-UR 12-00618).
sepiolite, palygorskite, Sevilleta Long Term Ecological Research Site, Rio Grande Rift, pedogenic carbonate, stable carbon isotopes, stable oxygen isotopes, calcic soils, soil pisoliths, petrocalcic, petrogypsic, soil carbonate
Bryan-Ricketts, Debra. "Soil geomorphology of the eastern Sevilleta Long Term Ecological Research Site." (2012). https://digitalrepository.unm.edu/eps_etds/8