TEXTURAL CHARACTERIZATION AND AGE CONTROL OF CLAY DUNES ON THE RIO GRANDE DELTA

Clay dunes are unique eolian landforms that differ from other types of dunes by their large percentage of clay. While initially described in South Texas, recent work has also identified them in Australia, Africa, and China. This work focuses on the clay dunes located on the Rio Grande Delta sub-humid regions of the coastal lagoons in Texas, specifically on the Rio Grande River to Corpus Christi. Locally known as lomas, these dunes form elevated landforms within the otherwise flat Delta plain, resulting from the accumulation of fine-grained intertidal sediments transported by the prevailing Southeasterly winds. The lomas support endemic plant assemblages and provide habitat for wildlife species, including the endangered ocelot (Leopardus pardalis albescens). Despite being geologically rare and ecologically important, the clay dunes in the Rio Grande Delta remain poorly understood; basic questions regarding their age, rates of accretion, and the role of burrowing animals in the adjacent tidal plains remain unanswered. Here we present the first textural characterization and age control of a large dune exposed by State Highway 48, which traverses the delta. We use grain size analysis, loss-on-ignition, x-ray-fluorescence, and radiocarbon dating to provide constraints on the timing formation. The outcomes of this study will enhance the geological understanding of clay dunes and contribute to their preservation.