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Pacific Coastal & Marine Science Center

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

Cross-Bedding, Bedforms, and Paleocurrents

Dip plots, static images, and captions

View Animation

Dip plot; see caption below.
Static image of cross-section; see caption below.

FIG. 21.  Structure formed by bedforms that reverse direction of migration and undergo net migration. 

RECOGNITION: This structure is similar to those produced by bedforms that reverse asymmetry while migrating (FIG. 22).  The two kinds of structures can be distinguished, because reversals in asymmetry cause cross-beds to offlap and onlap the erosion surfaces within each set of cross-beds, whereas reversals in migration direction produce erosion surfaces with relatively concordant overlying beds, as shown here.  Although the cross- beds are truncated at different elevations, the preserved parts of the cross-beds all have the same shape, because bedform shape does not change through time.

ORIGIN: This structure requires flow conditions similar to those of the preceding computer-generated example (reversing migration direction without net migration), except that, in the example illustrated here, the flow has a long-term transport asymmetry in order to cause net migration of the bedforms.

 

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