Origin of Sandstone Casts in the Upper Triassic Zuni Mountains Formation, Chinle Group, Fort Wingate, New Mexico

Elongate (m-scale), cylindrical sandstone casts are common in the Upper Triassic Zuni Mountains Formation (basal Chinle Group) in a section near Fort Wingate, west-central New Mexico. Previous authors suggested that these features were formed by the burrowing activity of lungfish. Following abandonment of this hypothesis, it was proposed that the casts are the fossilized burrows of crayfish. We find evidence for this origin (crayfish body fossils and characteristic wall structures) lacking at this site. We propose alternatively that the casts are rhizoliths formed by the deep tap roots of the sphenopsid Neocalamites.