Relations Between Cross-Bedding, Bedforms, and Flow
The usefulness of cross-bedding as a flow indicator results from the connections between cross-bedding, bedforms, and flow conditions. As a result of empirical and theoretical studies in the past few decades, it is now possible to predict crudely what bedform morphology results from flow conditions for many two-dimensional flows that are steady through time and uniform through space and for many two-dimensional oscillatory flows. Eventually, it may become possible to predict bedform morphology and behavior accurately for more complicated flows such as those that vary in strength or direction or the geologically more important flows that decelerate downcurrent (Rubin and Hunter, 1982). Ultimately, it may be possible to use cross-bedding to recreate current-meter-type records of paleocurrent directions and velocities. Even without quantitative fluid dynamics models, however, it is possible to infer bedform morphology and behavior from cross-bedding and to relate those interpreted characteristics qualitatively to flow conditions. The following section considers the controls of flow on bedform morphology and behavior and considers some of the general properties of the cross-bedding that is produced.
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.