Preservation of Autogenic Processes and Allogenic Forcings in Set-Scale Aeolian Architecture I: Numerical Experiments

Abstract

A reduced-complexity aeolian dune stratification model is developed and applied to explore the role of dune morphodynamics in the creation of synthetic sections of aeolian stratigraphy originating from three sets of environmental forcing: 1) steady wind transport capacity, 2) steady bed aggradation and variable wind transport capacity, and 3) steady wind transport capacity and bed aggradation. In each scenario, the forward motion of initial, highly disorganized dunes generates a significant record exclusively containing autogenic signals that arise from early dune growth, deformation, and merging. However, continued dune growth scours deeply, and shreds all records of early dunes. Afterward, dunes self-organize into quasi-stable groups. Forward motion of dune groups creates, truncates, and amalgamates sets and co-sets of cross-strata, quickly forming a second, significantly more robust stratigraphic record, which preserves a comingling of signals sourced from ongoing autogenic processes and each scenario's specific set of environmental forcings, the allogenic boundary conditions of the sand sea. Although the importance of self-organization on modeled aeolian stratification is clear in the few presented scenarios, self-organization may be throttled via variability in environmental forcings, as thoroughly documented in a companion paper (Cardenas et al., this issue). Therefore, additional work is warranted because this numerical experiment only begins to sample possible sets of environmental forcing, boundary conditions, and initial conditions, geomorphic responses, and consequential preservation possible in the presented surface-stratigraphic bedform modeling framework.

The Effect of Remote Sensing Resolution Limits on Aeolian Sandstone Measurements and the Reconstruction of Ancient Dune Fields on Mars: Numerical Experiment Using the Page Sandstone, Earth

“…The distributions of cross‐set thicknesses are characterized using statistical moments (mean, standard deviation, and products thereof), distribution shapes, and the number of detected sets. The ancient environment and dune‐field dynamics recorded by the Page Sandstone are well characterized (Cardenas et al, ; Swanson et al, ), and we compare these true characterizations to reinterpretations based on the experimental, resolution‐limited distributions. To judge the significance of these altered interpretations, we compare the experimental results to data from the Jurassic Entrada Sandstone, which represents an opposite end‐member wet dune‐field accumulation to the dry Page dune fields.…”

“…The thickness distributions of aeolian cross sets are among the easiest stratigraphic data to collect, and the shape of the distribution, as well as its statistical moments, records the aggradation, migration, and the size of dunes in a field (Bridge, ; Bridge & Best, ; Cardenas et al, ; Jerolmack & Mohrig, ; Paola & Borgman, ; Rubin & Hunter, ; Swanson et al, ). Wind is the dominant driver of sediment transport on modern Mars (Ewing et al, ; Fenton & Hayward, ; Silvestro et al, ; Silvestro et al, ; Chojnacki et al, ; Day & Kocurek, ; Lapotre et al, ; Cornwall et al, and Cornwall et al, ; Chojnacki et al, ) and has likely been significant throughout the planet's history (e.g., Anderson et al, ; Banham et al, ; Day & Catling, ; Day & Catling, ; Grotzinger et al, ; Kite et al, ; Lewis et al, ; Lewis et al, ; Milliken et al, ).…”

“…Therefore, aeolian strata are likely to provide a rich source of information about conditions at the ancient surface of Mars. This information is encoded particularly well into cross‐set thicknesses (Cardenas et al, ; Jerolmack & Mohrig, ; Paola & Borgman, ; Swanson et al, ). Aeolian cross sets are observable on Mars from remote sensing images and digital elevation models (DEMs; e.g., Milliken et al, ; Anderson et al, ; Day & Catling, ), but we hypothesize that resolution limits could lead to remotely measured thickness distributions that are not representative of the true distribution.…”

“…In aeolian dune fields, the controls on dune cross‐set accumulation represent a mix of naturally occurring processes inherent to aeolian sedimentary systems (autogenic processes) and external, environmental forcings. Autogenic processes include dune interactions (Day & Kocurek, , ; Ewing & Kocurek, , ) and natural variation in dune scour depths (Bridge & Best, ; Cardenas et al, ; Jerolmack & Mohrig, ; Paola & Borgman, ; Swanson et al, ). Environmental forcings or boundary conditions include wind regime, atmospheric conditions, sediment availability and source geometry, basin geometry, the proximity of the water table to the surface, and antecedent topography (Kocurek et al, ; Cardenas et al, ; Chojnacki et al, ; Ewing et al, ; Swanson et al, ).…”

“…As such, the variability in set thickness is greater than the variability in dune scour depths. In contrast, laterally continuous, climbing cross sets record steady bed aggradation and will not favor the preservation of cross sets filling the deepest scours strongly, meaning a greater percentage of dunes have preserved cross sets (Allen, ; Bridge & Best, ; Jerolmack & Mohrig, ; Leclair et al, ; Rubin & Hunter, ; Swanson et al, ). As a result, the variability in cross‐set thickness is closer to the variability in dune scour depths.…”