The palaeoenvironmental significance of dune size hierarchies

The size of a dune is a function of many factors, one of which is the length of the period of consistent wind regime under which it grew. Ephemeral dunes are defined as those that are adjusted to diurnal wind regimes, meso-dunes to annual wind regimes, and mega-dunes to wind regimes that persist for longer periods. These longer periods could be major climatic cycles, but there seem to be no dunes whose size reaches that allowed by the length of some of these periods. There may, therefore, be a maximum size beyond which mega-dunes cannot grow, dictated by sand supply, aerodynamic processes such as speed-up, or by the scale of the atmospheric boundary layer. These concepts are tested on dunes in the Wahiba Sands in Oman, analysed from a Landsat image. It is hypothesised that a large set of megadunes here formed in the LGM, that a smaller set of mega-dunes may be of Younger Dryas age, and that there is a meso-dune series of Holocene age.