Burrows of invertebrate animals are extremely abundant within eolian sandstone
at two stratigraphic intervals of the Early Jurassic Navajo Sandstone on the
northern Paria Plateau near the Arizona-Utah border.
The burrows are within both dune and interdune sandstones. Much
of the rock within the intervals is completely bioturbated (ichno-
fabric index of 5 sensu Droser and Bottjer, 1989).
Some of the burrows are clustered. These might represent the
emergence of young insects from a multi-chambered nest.
Vertebrate tracks are also present within the bioturbated zones. This trackway
(Brasilichnium) was made by a mammal-like reptile ascending an angle-of-
repose slope. Note grainflow strata above and below the tracks.
This view is downdip and shows tracks in cross-section within grainflow strata .
These are theropod tracks (Grallator) at the top of a 7m-thick set of grainflow
The bioturbated zones represent times when the water table was mounded
under the dunes and wet interdunes supported plant and animal life.
The upper set of cross-strata contains annual depositional cycles, but
has no trace fossils. The two lower sets also contain annual cycles, but
also contain abundant burrows and tracks.
The burrowed zones are interpreted as records of two long-lived pluvial intervals
during deposition of the Navajo Sandtstone, similar to the early Holocene pluvial
of North Africa.