Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars

Abstract

The Mars Science Laboratory rover Curiosity visited two active wind‐blown sand dunes within Gale crater, Mars, which provided the first ground‐based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial‐like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large‐ripple lee slopes. Lee slopes were ~29° where grainflows were present and ~33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter‐scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune‐field pattern dynamics and basin‐scale boundary conditions will dictate the style and distribution of sedimentary processes.

Surface Roughness and Gravitational Slope Distributions of Vesta and Ceres

“…If we compute the histogram of slopes for a less active portion of the dune field, the local maximum is less prominent or becomes a kink at the same slope similar to what we see in global histograms (Figure ). Similarly to Atwood‐Stone and McEwen () and Ewing et al (), we find that the location of the local maximum in the histogram of slopes for the Martian dunes is consistent with that of the terrestrial dunes. In general, the histograms for the Martian and terrestrial dunes are remarkably similar.…”

Compositional variations in sands of the Bagnold Dunes, Gale crater, Mars, from visible‐shortwave infrared spectroscopy and comparison with ground truth from the Curiosity rover

“…Untangling the effects of mineral abundances, grain sizes, and dust cover from orbit remains difficult, and ground truth is required to definitively exclude the possibility that compositional variations merely indicate differences in masking of the primary mineralogy by dust. The Bagnold Dunes were previously determined to be generally dust‐free [ Rogers and Bandfield , ], are relatively active near the rover traverse (e.g., Figure c) [ Silvestro et al , , ; Bridges et al , ; Ewing et al , ] with dune displacements of about half those measured in the very active Nili Patera dune field [ Bridges et al , ], and HiRISE red/infrared band ratios are relatively high over the dunes (Figure b). In the following section, we quantitatively constrain the modal composition of bulk sands at four locations, assuming that the Bagnold sands are relatively dust‐free (an assumption later discussed in section 4.2).…”

Aeolian saltation on Mars at low wind speeds

“…For Mars experiments, the adopted representative grain is 100 μm with mafic density of 3000 kg/m 3 . This approximate grain size and composition appears to be volumetrically most important in active impact ripples at Meridiani Planum, Gusev crater, and Gale crater [ Soderblom et al ., ; Sullivan et al ., , ; Ehlmann et al ., ; Ewing et al ., ] (see also Figure ). Figure shows numerical experiment results for three Martian cases using 100 μm mafic grains for which u *ti = 0.12 m/s and u *tf ~ 1.8 m/s [ Renno et al ., ; Iversen and White , ].…”