Grain fabric of a laboratory antidune

The grain fabric of a laboratory antidune composed of coarse- to medium-grained sand shows a high-angle upcurrent imbrication both on the upstream and downstream sides. Such a grain fabric differs from a normal dune or a megaripple, where grain alignment displays an upcurrent imbrication relative to the depositional slope in the foreset lamina and/or near parallelism with the slope surface in the toe-set lamina. Recognition of antidunes in ancient rocks is difficult, but detailed examination of grain fabric of cross-stratification makes it possible to distinguish antidunes or ‘backset’ bedding from normal dunes or megaripples.