EOLIAN WEATHERING MICROTEXTURES ON SANDS OF DIFFERENT MINERALOGIES

Microtextures on the surfaces of sand grains can be diagnostic of the environment the grain was in and the chemical and physical processes they have been exposed to. Eolian environments are dominated by mechanical weathering but are influenced by small amounts of chemical weathering. Eolian quartz sand grains are well represented in literature, but there is very limited published research on the microtextures present on other types of monomineralic grains. There exist eolian systems composed of nearly 100% of a mineral other than quartz; this study compares examples of monomineralic sands composed of quartz, calcium carbonate, and gypsum.

This project examines the hypothesis that monomineralic sands will exhibit different weathering textures in eolian environments that reflect the chemical and physical properties of the mineral. The first sample, from the Fertile Dune Field (FDF) in Minnesota, USA, is (>95%) quartz, upper fine to medium sand, well sorted, and a mix of well-rounded and angular grains. The second sample, collected at French Bay on San Salvador Island, Bahamas from a foreshore dune, is composed of calcium carbonate, medium sand, and is well-sorted. A calcium carbonate beach sample was also collected for comparison. The third sample, collected from White Sands National Park in New Mexico, USA, is gypsum, a coarse sand, well sorted, and a mix of angular to rounded grains. The samples were carbon coated for SEM analysis, but no other sample preparation was done so as not to risk destroying any existing microtextures. Vos et al. (2014) conclude that the most common eolian microtextures on quartz are rounded edges, bulbous edges, upturned plates, low relief, abrasion fatigue, crescentic percussion marks, meandering ridges, elongated depressions, and adhering particles. All these features except for crescentic percussion marks were identified on the FDF quartz. The calcium carbonate exhibited most of the same features or analogous features despite a much shorter transport distance and different mineralogy. The gypsum exhibited adhering particles, bulbous edges, and rounded grains, but overall displayed fewer textures analogous to those found on quartz sands.