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Pacific Coastal & Marine Science Center

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

Cross-Bedding, Bedforms, and Paleocurrents

Photographs

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

FIG. 7.  Structure formed by ripples climbing at stoss-erosional, stoss-depositional, and vertical angles; fluvial deposits of the Colorado River, Grand Canyon National Park, Arizona.  The analogous computer-generated structures are shown in Figures 3-5. Note pencil for scale.

RECOGNITION: In this example the angle of climb was at times stoss-erosional (E), stoss-depositional (D), and vertical or slightly upcurrent (V).  This systematic change in ripple behavior indicates a change in flow conditions, but other variations in the structure are more random and therefore probably represent differences in behavior or morphology of individual ripples.  For example, one ripple apparently decayed while migrating; that ripple migrated from the lower right side toward the center of the photograph, at which point the ripple height decreased so much that the ripple almost disappeared. In the overlying deposits (where the ripples climb vertically), a new ripple appeared in the same part of the ripple train.  From this single vertical section it is impossible to determine whether these appearances and disappearances are real changes through time in the ripple train or whether they are merely apparent changes caused by migration of three-dimensional bedforms obliquely through the outcrop plane.

 

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