Internal sedimentary structure of linear dunes modelled with a cellular automaton

Yukun Liu,Andreas C W Baas

doi:10.1111/sed.12767

Abstract

AbstractLinear dunes are the most common type of dune found on Earth and exist on several extra‐terrestrial bodies, but despite this abundance their internal stratigraphy has not been commonly agreed. A cellular automaton is deployed to simulate the development of linear dunes, starting from a flat bed, under bi‐modal oblique wind regimes of varying degrees of asymmetry. The internal stratigraphy of the linear dunes is monitored by keeping track of (buried) erosion surfaces, avalanche deposits and vertical accumulation, as well as the age of last subaerial exposure of the sediments. The simulations show the initial pattern‐coarsening of a network of small dunes into fewer larger longitudinal ridges via bedform interactions and Y‐junction dynamics. Three newly recognized types of bedform interaction are identified that relate to initial Y‐junction dynamics: longitudinal crest‐splitting, which creates free dune tips that can interact with adjacent dunes, and laterally oscillating interactions that lead to ephemeral Y‐junctions (normal or reverse). The results show that these three bedform interactions leave no persistent signatures in the stratigraphic record. However, a further three bedform interactions involving the superposition of one dune onto another – merging, cannibalizing and repulsion (known from transverse dune field dynamics) – do leave specific evidence in the internal stratigraphy of the remaining dune, a buried interaction surface at a specific inclination. The preservation potential of this interaction surface varies between the three types. After the initial pattern‐coarsening phase, the linear dunes become larger and more independent and their crest orientation follows the net resultant transport direction. The stratigraphies of mature dunes under wind regimes of differing asymmetry show that under (nearly) symmetrical winds the dune accumulates mainly vertically, with strata dipping parallel to the flanks, while under more asymmetrical wind regimes the internal stratigraphy resembles that of transverse dunes.

Highlights

It is commonly recognized that linear dunes are the most abundant dune type on Earth (e.g. Lancaster, 1982; Craddock et al, 2015) and exist on extra-terrestrial bodies like Titan and Mars (e.g. Lorenz et al, 2006; Rubin & Hesp, 2009; Radebaugh et al, 2010)
The internal sedimentary structure of the linear dunes is jointly shaped by bedform interactions and the wind regime
The simulation results reported here reveal a variety of stratigraphic signatures as a consequence of linear dune field pattern coarsening via bedform interactions, as well as more mature independent linear dunes

Summary

Introduction

It is commonly recognized that linear dunes are the most abundant dune type on Earth (e.g. Lancaster, 1982; Craddock et al, 2015) and exist on extra-terrestrial bodies like Titan and Mars (e.g. Lorenz et al, 2006; Rubin & Hesp, 2009; Radebaugh et al, 2010). The signatures of pattern coarsening during the subsequent model years are mostly preserved in the stratigraphy, but eventually all sand in the domain is reworked over longer periods of time, due to lateral migration and bedform interactions.

Results

Conclusion