Surface textures of quartz and ilmenite grains from dune and beach sands of the Gulf of Mexico Coast, Mexico: Implications for fluvial, aeolian and marine transport

摘要

Surface textures of quartz and ilmenite grains provide an insight in assessing current mechanical, chemical and mechanical-chemical processes in dune and beach sands of the Gulf of Mexico Coast (GMC) Mexico. The GMC area produces hybrid sands enriched in monocrystalline quartz and ilmenite-free grains. Quartz grains are observed in all dunes and beach localities of the central GMC close to the Trans-Mexican Volcanic Belt characterized by large conchoidal fractures (> 100 mu m), angular to subangular outlines, arcuate steps, high relief, and sharp edges associated with fluvial transport. Aeolian quartz features like meandering ridges, upturned plates, bulbous edges and adhering particles on quartz are only present in some GMC sites, whereas marine surface textures like straight and curved grooves are sparse. Chemical surface textures on quartz and ilmenite are a consequence of silica saturated low-energy subaqueous conditions and subaerial exposure, diagenesis and intermediate weathering processes in the dunes and beach sands. Ilmenite grains are common in all studied localities of the GMC, characterized by large conchoidal fractures (> 100 mu m), angular to subangular outlines, flat cleavage surfaces, arcuate steps and high relief. In some ilmenite grains, upturned plates, meandering ridges, bulbous edges and abrasion fatigue characterize aeolian surface features. Straight and curved grooves only characterize marine surface textures. To assess the prevailing transport mechanisms along the GMC, quartz and ilmenite grains from dunes and beach sands were selected based on surface texture observations. Our findings suggest that quartz and ilmenite grains are primarily transported and deposited along the coast by riverine input, a second-cycle of aeolian transport onshore, and recycling by marine longshore currents and waves.