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 dune. But because their development and their internal structure are poorly understood, they are rarely recognized in the rock record. Models of linear dune development 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. 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.

Geomorfologia e arquitetura deposicional de uma planície de cordões litorâneos na margem NE da Lagoa dos Quadros, RS, Brasil

“…Ainda na costa do Rio de Janeiro, radarfácies semelhantes foram descritas por Moulton et al (2013), num estudo sobre a gê-nese e morfologia de dunas frontais. Cabe ressaltar trabalhos precursores de GPR associados à fácies eólicas, como Bristow et al (2000aBristow et al ( , 2000b.…”

Temporal and spatial variability in dune reactivation across the Nebraska Sand Hills, USA

“…This reconstruction showed that with lateral migration taken into account, linear dune internal structures could look remarkably like those of transverse dunes (Rubin and Hunter, 1985). Bristow et al (2000) used ground penetrating radar (GPR) in combination with OSL and found evidence for lateral migration in linear dunes in Namibia, mapping offset stacks of cross-beds in different directions, indicating repeated lateral shifts in two directions. A recent study in Inner Mongolia observed lateral migration in oblique dunes over a period of 3 years while monitoring an area that had been flattened at the start of the study (Ping et al, 2014).…”

A semi-analytical model for form drag of river bedforms

“…It may be expected that the semi-analytical form drag model is applicable to unidirectional flow over desert sand dunes originated by wind, as these dunes may have the same asymmetric shape as the bedforms considered in this thesis, and may cause flow separation (e.g. Bristow et al, 2000).…”