The sedimentary structure of linear sand dunes

Abstract

Linear sand dunes—dunes that extend parallel to each other rather than in star-like or crescentic forms—are the most abundant type of desert sand dune¹. But because their development and their internal structure are poorly understood, they are rarely recognized in the rock record². Models of linear dune development^2,3,4,5,6 have not been able to take into account the sub-surface structure of existing dunes, but have relied instead either on the extrapolation of short-term measurements of winds and sediment transport or on observations of near-surface internal sedimentary structures. From such studies, it has not been clear if linear dunes can migrate laterally^2,7,8. Here we present images produced by ground penetrating radar showing the three-dimensional sedimentary structure of a linear dune in the Namib sand sea, where some of the world's largest linear dunes are situated. These profiles show clear evidence for lateral migration in a linear dune. Moreover, the migration of a sinuous crest-line along the dune produces divergent sets of cross-stratification, which can become stacked as the dune height increases, and large linear dunes can support superimposed dunes that produce stacked sets of trough cross-stratification. These clear structural signatures of linear dunes should facilitate their recognition in geological records.