DUST-DOMINATED CUMULIC ARIDISOL PEDOGENESIS DOMINATED THE PLIOCENE TAOS PLATEAU, NEW MEXICO, USA

The Taos Plateau in New Mexico, USA, contains multiple Pliocene intermediate to mafic lava flows covering 100’s of km² associated with Rio Grande Rift volcanism. Atop some of these lava flows, sediments were deposited and over time soils formed in these sediments. These soils were subsequently buried by later lava flows, becoming encased and incorporated into the rock record as paleosols. In this study, our goal is to determine the climate conditions under which these soils formed, the duration of pedogenesis, and the overall geomorphic setting of the Taos Plateau during the Pliocene epoch. The composition, texture, and morphological features of these paleosols suggests that they are not residual. In fact, the underlying basalts and basaltic andesites are essentially unweathered. Instead, these soils formed in and were subsequently inflated by eolian-transported and –deposited dust. The most common mineral constituent of the silt- to fine sand-sized parent material and paleosol horizons is quartz, a mineral absent in the encapsulating basalts. Our results suggest that these paleosols formed in a semi-arid environment, similar to what is found in present day New Mexico. The presence of stage III-IV pedogenic carbonate horizons suggest a duration of pedogenesis of up to 10⁵ years under reasonably stable semi-arid paleoclimate conditions. Within several of the paleosol layers we observed inflationary horizons with well-preserved desert pavement. Our radiometric dating of encapsulating basalts provides further constraints on duration of pedogenesis and timing of pedogenic, depositional, and volcanic events.