Conceptual Mineral Genesis Models for Calcic Pendants and Petrocalcic Horizons, Nevada

Abstract

We use the very old, extant, Stage VI Mormon Mesa petrocalcic soil profile in southern Nevada to: (i) present a conceptual model summarizing known spatial and temporal relationships among authigenic calcite (or low-Mg calcite), palygorskite and/or sepiolite, and amorphous silica and (ii) adapt a second model to describe the occurrence of pedogenic barite and the effect of climate oscillations on soil mineralogy at Mormon Mesa. These conceptual models, one compiled from previous research, one built from new data in this study, directly address the importance of dust to soil genesis, especially the control of salt flux and high pH on Ba, Si, and Al mobility in alkaline soil solutions. Authigenesis of calcite and palygorskite/sepiolite creates positive feedbacks with soil solution chemistry that drives further mineralogical development. We explain the occurrence of pedogenic barite at Mormon Mesa based on higher Ba solubility and translocation into the soil profile with increased concentrations of Cl and Mg in soil solutions during interpluvial climates. Development of integrated, mineral development models illustrates individual system components and/or processes that should be targeted for future chemical, biological, geochronologic, or micromorphological study, and provides a basis for comparison of calcic soil genesis from disparate sites around the world.