Uniqueness of Solutions
The usefulness of the following computer-generated cross-bedding images depends on the uniqueness of the results. Specifically, can more than one structure result from a specific depositional situation, or can more than one depositional situation produce similar structures? The answer to the first question is that only one structure can result from a given depositional situation, if the bedform morphology and behavior are described in sufficient detail. If the situation is merely described qualitatively, many structures can result. For example, Fi gure 46 illustrates 14 different structures produced by main bedforms with superimposed bedforms migrating toward a diverging direction. In other words, no single image can represent all structures formed by a particular depositional process.
More serious interpretive problems arise if two or more depositional situations can produce the same structure; interpretation of real bedding structures then becomes equivocal. Such is certainly the case if the bedding structures are not observed in three dimensions. As illustrated in the following section, grossly different processes can produce structures that are virtually indistinguishable in a single two-dimensional exposure. In contrast, the computer experiments illustrated in the following figures suggest that structures that are similar in three dimensions are rarely produced by different processes.
Figures & Tables
The computer modeling that forms the basis for this publication was undertaken to relate the geometry of cross-bedding to the morphology and behavior of bedforms. Using computers for this purpose is necessary only because sedimentologists cannot adequately visualize the geometry arising when complex, changing surfaces move through space. Images range from the complicated, which will be of interest to sedimentologists who have had experience interpreting cross-bedding or studying the behavior of bedforms, to simpler illustrations the can convey an understanding of the origin of cross-bedding geometry even to those not experienced in the field.