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.