INVESTIGATING GYPSUM SAND TEXTURES TO IMPROVE THE SUITABILITY OF EOLIAN MATHEMATICAL MODELS

Most desert dunes on Earth today are composed of quartz sand. Thus, existing mathematical models that predict the physical sedimentology of eolian processes are based on characteristic properties of quartz grains in modern dunes, including fine sand size, high sphericity, well-roundedness, and quartz density. Some desert dunes, however, are composed of gypsum grains. Applying existing, quartz-based models to gypsum dunes is problematic; gypsum eolian sand originates from crystals grown at the surface that have not typically had much time or distance to be reworked, relative to quartz, which generally has previously formed millions of years earlier, deep below the Earth's surface, and has undergone extensive transportation through many environments prior to becoming eolian quartz sand. Furthermore, gypsum and quartz differ in hardness, density, and cleavage; gypsum is softer , less dense, and contains greater variance in sphericity and roundness compared to quartz. For this study, 398 grains from the Dome Dune located in White Sands National Park (New Mexico) were described. Grain size, roundness, sphericity, and geometric properties were recorded. Statistical analysis was conducted to determine representative grain texture parameters. While some dunes are composed of well-rounded and spherical gypsum grains, dunes closest to Lake Lucero, like Dome Dune, are bladed, rod-shaped, or flake-shaped. Gypsum grains range from granule-sized to coarse sand-sized. Preliminary results suggest that traditional mathematical models based on quartz sand grains are not suitable for modeling gypsum sand grains. To better recognize the eolian origin of some clastic gypsum and other chemical sediments in the rock record, it is important to develop alternative mathematical models that are more suitable for the characteristic properties of these sediments.