ABSTRACT: Modeling the Development of Eolian Stratigraphy Via Simulation of Multiple Grain-Size Saltation: An Update

Robert S. Anderson, Peter K. Haff

Numerical simulation of the eolian saltation process has produced tightly constrained probability distributions of hop lengths, impact angles, and speeds, as well as the total numbers of grains in saltation, for any

given combination of grain size, density, and wind speed. These distributions allow modeling of two processes important to the development of stratigraphy in eolian sandstones: (1) ripple formation and translation, and (2) the pattern of deposition on the lee sides of sand dunes. We focus on the ripple problem.

More recently, the saltation simulations have been extended to incorporate mixtures of grain sizes. When incorporated into the ripple and lee-side models this should allow the production and evolution of stratigraphy associated with grain size variations. We discuss the general modeling strategy, advocating the simulation of stratigraphic development through the use of a calculation space that is finely divided into discrete elements. This division reflects the control of the eolian saltation system by the impacts of individual grains with the granular substrate, which therefore, depend solely upon the local topography.

We present illustrative examples of both multiple grain-size saltation and ripple simulations. We also explore possible explanations for the tendency of coarse grains to remain at ripple crests, as well as the role of crest-coarsening in controlling the final ripple dimensions and shape.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990