Pacific Coastal & Marine Science Center
Bedform Sedimentology Site: “Bedforms and Cross-Bedding in Animation”
FIG. 11. Structure formed by ripples climbing at a lee-erosional angle; fluvial deposits of the Colorado River, Grand Canyon National Park, Arizona.
RECOGNITION: The rippled surface at the top of the light-colored sand was formed when ripple migration was accompanied by net erosion; the ripples scoured into the underlying flat-bedded sand. This erosional structure was preserved when the rate of deposition became positive, thereby causing the ripples to climb at a positive angle. The change from net erosion to net deposition coincided with an increase in silt content in the sediment. In the Grand Canyon, silt content increases during floods, suggesting that the change from erosion to deposition at this site was caused by a pulse of silty flood sediment.