Bedforms: ripples and dunes

Ripples, dunes, antidunes are all bedforms, structures that form in sand when it is moved by water or wind. Bedforms are ubiquitous on our planet. It is very common to see ripples, undulatory structures in sand, under shallow waters close to seashores or along riverbanks. And deserts, they are commonly covered with large sand dunes, in turn sprinkled by smaller sand waves, all structures produced by wind. All these structures have a strong preservation potential and can survive in the rock record, either as fossil ripple marks, visible on the surface of strata, or, more commonly, as various types of cross-bedding, inclined laminae and layers that represent cross-sections through past migrating bedforms.

One of the fundamental principles of geology is that the present is the key to the past. In the case of bedforms, this means that we can study the bedforms that currently form on our planet to understand how past sedimentary environments looked like, thanks to the structures preserved in sedimentary rocks. In particular, bedforms are accurate storytellers of the direction and strength of currents in past environments.