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Pacific Coastal and Marine Science Center

Bedform Sedimentology Site: “Bedforms and Cross-Bedding in Animation”

Cross-Bedding, Bedforms, and Paleocurrents


Photo of rock or sand showing pertinent structure or structures; see caption below.

FIG. 70.  Migrating, stoss-erosional, lee-depositional, oblique oscillation ripples; Moenkopi Formation (Triassic), Capitol Reef National Park, Utah.

RECOGNITION: An oscillatory-flow origin of these ripples is suggested by ripple symmetry and by the relatively two- dimensional morphology of the ripples.  Migration of the ripples toward the upper right of the photograph was accompanied by erosion on the ripple stoss sides (lower left) and deposition on the lee sides (upper right); erosion on the stoss sides has exposed beds that were deposited on the ripple lee sides when the ripples were positioned to the lower left.  Erosion of the ripple flanks was more severe on ripple flanks facing toward the left than on flanks facing toward the bottom of the photograph.  This feature suggests that the crestline sinuosities were migrating with a longitudinal component of transport (from left to right along the ripple crestlines), as simulated in Figure 69.  The resultant transport direction thus is oblique to the trend of the ripples, in the general direction indicated by the arrow.  If the individual oscillations in the flow that created these bedforms transported enough sediment to cause reversals in ripple asymmetry, then Figure 69 may be a realistic simulation; if the individual flow oscillations were too brief or too weak to transport enough sediment to effect ripple asymmetry, then the ripples may have behaved as invariable bedforms.


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