Pacific Coastal & Marine Science Center
Bedform Sedimentology Site: “Bedforms and Cross-Bedding in Animation”
FIG. 26. Cyclic compound cross-bedding inferred to have been produced by small dunes migrating down the lee slope of a larger dune; Navajo Sandstone (Upper Triassic? and Jurassic), Zion National Park, Utah.
RECOGNITION: Lack of basal wedges, lack of upcurrent-dipping cross-beds near the base of the set, and lack of upslope-migrating superimposed ripples suggest that this deposit was formed by downslope-migrating superimposed bedforms (FIG. 25) rather than by cyclically reversing flows (FIG. 22). If this interpretation is correct, field measurements should show that the cross-beds deposited by the superimposed bedforms dip in slightly different directions from the bounding surfaces scoured by the superimposed bedforms, as illustrated in Figures 65 and 66; cross-beds and bounding surfaces produced by superimposed bedforms can have the same dip direction only if crestlines of the superimposed bedforms exactly parallel the crestline of the main bedform (FIG. 25).