Long‐Lived Pluvial Episodes during Deposition of the Navajo Sandstone

Abstract

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.

Inconsistencies Between Pangean Reconstructions and Basic Climate Controls

“…These wind and biotic patterns persisted through the Early Jurassic (11). During the entire interval, the dominant winds in the north came from the northeast, curving to become northwesterly over the southern portion of the outcrops.…”

First reported actinopterygian from the Navajo Sandstone (Lower Jurassic, Glen Canyon Group) of southern Utah, USA

“…Although it is conceivable such water depths in the Navajo could have occurred, the fish material presented here can only in the broadest sense tell us that water depth was deep enough to support a small population of moderate-sized fishes for more than a single year. Some interdune deposits in the Navajo have been interpreted as fluvial in origin (Loope and Rowe, 2003). Because these fish must have dispersed to this particular interdune lake from some larger body of water, further work on Navajo interdune deposits may reveal more about how these localized habitats were connected during wetter periods in the Early Jurassic erg.…”

Paleontology of the Bears Ears National Monument: history of exploration and designation of the monument

“…Outside of the BENM area in southern Utah, Navajo Sandstone invertebrate and vertebrate traces are numerous, including an important and extensive trackway locality at the Kayenta-Navajo boundary in Lisbon Valley (Stokes, 1978;Lockley et al, 1992;Lockley and Hunt, 1995;Rainforth, 1997;Loope and Rowe, 2003;Loope, 2006a;Ekdale et al, 2007). Particularly notable are spring-fed interdunal pond deposits that are associated with fossils of large conifer logs, leaves, ostracods, invertebrate and vertebrate burrows, and dinosaur tracks (Eisenberg, 2003;Loope et al, 2004;Lucas et al, 2006a;Parrish and Falcon-Lang, 2007;Riese et al, 2011;Parrish et al, 2017).…”