PEDOGENIC BARITE, PALYGORSKITE, AND SEPIOLITE IN PETROCALCIC HORIZONS AT MORMON MESA, NEVADA: IMPLICATIONS FOR SOIL WATER MOVEMENT

Petrocalcic soil horizons are used to interpret landform stability and flooding hazards, paleoclimate, and geologic and geomorphic processes related to their development through time. This study applies SEM/EDS and XRD analyses to examine the mineralogical characteristics of profiles that contain a stage VI petrocalcic horizon at Mormon Mesa, NV. Barite is present in 34% of the images viewed with SEM. The primary process responsible for the presence of barite in Mormon Mesa is the combination of barium and sulfate ions derived from the weathering and transport of dust at the surface that are flushed into the soil profile to combine and precipitate barite. When barite is present, it occurs in areas of relatively higher porosity 93% of the time. Areas of higher porosity include (i) areas of fibrous clay neoformation around and within grains and throughout the calcite matrix that creates a secondary microporosity (ii) areas of linear voids, and (iii) root pores. Pedogenic barite provides useful information regarding paleoclimate and related weathering/sedimentation cycles and morphologic evolution of highly indurated petrocalcic horizons. The complex development of these types of soils is important for our understanding of their physical and chemical response to natural and anthropogenic effects such as chemical and biological contaminants and climate change.