LIFE AND TIMES IN THE JURASSIC NAVAJO ERG SYSTEM: ADVANCES AND CHALLENGES

The Lower Jurassic Navajo Sandstone (Ss) of the Colorado Plateau is well known for its outstanding aesthetic landscape, application to understanding erg dynamics, and reservoir properties. Over the last decade, our focused studies on the Navajo Ss in the Moab area of southeastern Utah revealed four key discoveries that reflect the dynamic hydroclimate of this erg system. (1) Soft-sediment deformation is both common and widespread, signaling possible strong ground motion and groundwater under pressure that led to fluidization and liquefaction of erg sediments prior to deep burial. (2) Significant spring and pond deposits indicate an active hydrologic in the erg regime. (3) A descriptive hierarchy of surfaces from mm-scale eolian laminae up through m-scale bedsets and major surfaces of regional stabilization record autogenic through allogenic processes that bound eolian and non-eolian deposits. (4) Six biofacies based on the lithofacies associations of trace fossils and body fossils of microbes, plants, and animals record interactions within the terrestrial and aquatic food webs, which serve as proxies for water availability and effective precipitation or hydroclimate. Overall, these discoveries show how, in essence, fluvial, palustrine, and lacustrine depositional environments were not just transient in the erg but persisted for some time. Recognition of the individual structures, lithologies, biofacies, and bounding surface characteristics here are also applicable to other eolian systems and can be detected even in cores.

Recent studies on the Kayenta–Navajo transition across southern Utah suggest that climate change and aridification was not instantaneous, but likely transitioned over a period of time, in some cases spanning thousands of years based on the resiliency of the food webs. Unresolved issues still exist, including absolute age dating and regional to basin-wide stratigraphic correlations. Did this Jurassic erg system have greater global ramifications for Earth’s atmospheric system and dust distribution, which in our modern Earth benefits life in multiple places beyond the erg? The stories captured in the Navajo Ss offer opportunities for outreach and to share glimpses into the life and times of the Jurassic erg that capture the imagination across all age groups from tourists to geoscientists.