Pacific Coastal and Marine Science Center
Bedform Sedimentology Site: “Bedforms and Cross-Bedding in Animation”
FIG. 63. Structure formed by reversing, three-dimensional bedforms; one-half of a reversal cycle is shown.
RECOGNITION: The three-dimensional geometry of these bedforms results from superpositioning of features that might be called lee-side spurs, superimposed bedforms, or intersecting bedforms. If produced by waves, this assemblage of bedforms could be called interference ripples, diagonal ripples (Machida and others, 1974), or cross ripples (Clifton, 1976). The three-dimensional structure of these bedforms is evident from the circular foreset traces that are clearly displayed in the horizontal section. Reversals in migration direction of the main bedforms are visible on the vertical section that is transverse to the main crestlines. In this simulation, the small bedforms do not migrate along the troughs of the main bedforms; such migration would cause the structure to resemble the examples shown in Figure 46.
ORIGIN: This bedform morphology is most commonly produced by oscillatory flows, such as wave-generated flows and river eddies with oscillating reattachment points (Fig. 64).