ROOT TRACE PRESERVATION AND DISTRIBUTION IN THE LOWER JURASSIC NAVAJO SANDSTONE, SOUTHEASTERN UTAH AREA: IMPLICATIONS FOR NAVAJO HYDROLOGY, ECOLOGY, AND CLIMATE

The Lower Jurassic Navajo Sandstone in the Colorado Plateau region represents a portion of the largest sand sea the world has ever known. It also preserves a variety of rhizoliths (root traces) that serve as proxies for: 1) the presence of various sized plants; 2) soil formation; 3) the foundation of ecosystems; and 4) the local and regional hydroclimate. Four types of rhizolith preservation are represented in the area of Moab, Utah, and they occur in sandstone, siltstone, mudstone, and carbonate lithofacies associated with 1^st-, 2^nd-, and 3^rd-order eolian surfaces and supersurfaces. Rhizomats, rhizoliths, rhizohaloes, rhizotubules, and rhizocretions represent recurrent associations where incipient to well-developed pedogenesis took place as a function of daily, seasonal, annual, and/or ephemeral availability of water and animal activity. Rhizomats are nonpenetrative traces characteristic of lacustrine carbonate deposits representing short intervals of subaerial exposure. These incipient paleosols are dependent on the water table position at or just below the sediment surface, where plant growth in emergent areas supported invertebrate and vertebrate communities. Rhizocretions and rhizohaloes are penetrative traces that are most abundant in reddened fine sands and silts of interdune environments, often preserved as lenticular-shaped bodies associated with 1^st-order surfaces. Rhizohaloes are alteration halos of mostly herbaceous plant and shrub roots, whereas rhizocretions are concretions that preserve shrub and tree roots. Both of these root types represent incipient to moderately developed paleosols with seasonally sufficient water to support small to large and dense plant growth. Rhizoliths on 2^nd- and 3^rd-order surfaces are rare to common that likely represent water from dew formation and/or local, ephemeral rainfall events that flowed down or through the dune. Rhizoliths and rhizohaloes are also associated with incipient paleosols in fluvial and marginal lacustrine deposits representing periods of seasonal to annual occurring water from increased local or regional rainfall and/or elevated groundwater. All root-related features and their distribution record the ecologic interactions and sensitivity to water availability, as well as time for pedogenesis in the eolian environment.