DANCING ON THE DUNES: AN ICHNOLOGICAL EXAMINATION OF THE AZTEC SANDSTONE AND THE JURASSIC PALEOECOLOGY OF THE SOUTHERN NEVADA REGION

In recent years, multiple fossil trackways and preserved therapsid burrows have been reported across the Southern Nevada Region within the eolian dune deposits of the Jurassic Aztec Sandstone. These wind-blown sand-dune deposits are the southern- and western-most exposures of an ancient erg, active in the Early- to Middle-Jurassic, around 200-170 million years ago. The fossiliferous Nugget and Navajo Sandstones, exposed throughout much of the American West, composed the majority of this large sand sea. Despite being the leading-edge of one continuous erg system, the Aztec Sandstone had been deemed unproductive in prior paleontological studies. We suspect that monsoonal conditions along the western margin of Pangea promoted pluvial intervals that provided the necessary paleoecological conditions to support the diverse life that is being documented in these ancient dune deposits.

Sedimentological and ichnological features of interest occur in Red Rock Canyon National Conservation Area (RRCNCA), Valley of Fire State Park (VFSP) and Gold Butte National Monument (GBNM). Three-dimensional photogrammetric reconstruction of suitable trackways and their host rock will provide insight into the depositional environment and the potential that the Aztec Sandstone records multiple pluvial intervals at the time of erg deposition. By examining these reconstructions and field-collected data we can identify the behavior of the fauna present, as well as their relationship with the dynamic environment of this ancient sand sea.

Site AZ-059 records undertracks of at least two ichnogenera and is preserved in a large cross-bedded set with alternating 15 mm-thick grainfall and grainflow deposits. With 14 distinguishable trackways and associated sand-crescents this site provides the opportunity to study the track morphology and behavior of individual fauna, the biodiversity of the ecosystem, as well as the climatic and hydrologic characteristics of the environment.