Earth and Atmospheric Sciences, Department of


Date of this Version



Published in The Journal of Geology, 2003, volume 111, p. 223–232. Copyright 2003 by The University of Chicago. Used by permission.


The Navajo Sandstone of the American Southwest was deposited at approximately 190 Ma in a giant, subtropical dune field near the western margin of Pangea. From this unit, we report thick intervals of dune cross-strata that were churned by insects and trampled by reptiles. Although dunes continued to migrate freely, the distribution of trace fossils shows that plant life in wet interdune areas sustained high levels of animal activity on the dunes for many thousands of years. We interpret this suite of structures as the record of a pluvial episode climatologically similar to the period of “greening” in the Sahara 4000–10,000 yr ago. A high percentage of the rainfall on the Navajo erg recharged the water table and led to the development of highly dilute, local groundwater flow systems that discharged into interdune areas.