Photographs

FIG. 39.  Horizontal section through the deposit of a bedform with superimposed longitudinal spurs and scour pits; fluvial deposits, Colorado River, Grand Canyon National Park, Arizona.

RECOGNITION: The trend of the ripples that deposited these rib- and-furrow structures was roughly from left to right, and the ripples migrated toward the top of the photograph.  The two trough-shaped sets in the vicinity of the knife were filled relatively symmetrically and have axes that trend roughly normal to the strike of the somewhat straighter cross-beds at the top of the photograph, characteristics that are indicative of transverse bedforms (as simulated in FIG. 38).  In contrast, two sets of cross-beds (to the left) have been preferentially truncated on their right sides; when systematic, such preferential truncation is more typical of oblique bedforms (FIG. 46).