EXPERIMENTAL NEOICHNOLOGY OF BURROWING ARTHROPODS IN EOLIAN ENVIRONMENTS

In desert dune settings, body fossils are generally rare, leaving the bulk of interpretations of ancient eolian ecosystems to be based on the ichnofossils preserved in a variety of lithofacies. While some of these ichnofossils, such as vertebrate tracks, are relatively simple to interpret, there are many ambiguous subsurface bioturbation structures that are not well understood. Among animals studied in modern eolian environments, arthropods are the most common bioturbators and are, therefore, the most likely producers of these structures. Recent studies utilizing laboratory-based neoichnological experimentation have been able to bridge the gap of understanding between observed behaviors, environmental conditions, and the three-dimensional morphology of burrows produced by different continental animals. However, most eolian ichnofossils are only expressed in two-dimensions and were likely produced in loose substrates that do not conform to these experiments. This study examined the activities, behaviors, and two-dimensional bioturbation structures produced by six arthropod species, Hogna lenta, Orthoporus ornatus, Galeodes arabs, Smeringurus mesaensis, Stenopelmatus fuscus, and Eleodes armata, in loose sandy sediment of varying composition and moisture levels. Sediment composition varied in the proportion and distribution of sand, silt, clay, and organic matter. Sediment moisture content varied in ranges from 0-5%, 8-12%, and 15-25%. Throughout the experiments, structures produced by the arthropods were photographed and described both qualitatively and quantitatively. Active substrate disturbance activities were observed and recorded as well as behaviors associated with bioturbation structures. Biogenic fabrics from each trial were compared between all six species and between different sediment conditions (moisture and sediment composition). Biogenic structures produced in these experiments were compared to indistinct burrows and biofabrics from the Jurassic Navajo, Entrada, and Nugget Sandstones to help with their interpretation. Identifying the varying behaviors and organisms that produce two-dimensional structures will aid in future interpretation of cryptic bioturbation in eolian deposits.