Photographs

FIG. 62.  Zig-zag structure deposited by dune with reversing lee-side spurs and scour pits; Navajo Sandstone (Upper Triassic? and Jurassic) near Escalante, Utah.

RECOGNITION: The set of cross-beds in the center of this photograph was deposited by a dune that migrated into the plane of the outcrop.  While the dune was migrating, lee-side spurs and scour pits reversed migration direction or asymmetry, thereby creating the zig-zagging sets of cross-beds.  Numbers identify the sequence in which specific sets were deposited.  Note the alternating dip directions (sets 1 and 3 dip to the left in the outcrop plane; sets 2 and 4 dip to the right).  The set of zig-zags is approximately 10 m thick.