Evidence for Fluctuating Wind in Shaping an Ancient Martian Dune Field: The Stimson Formation at the Greenheugh Pediment, Gale Crater

Abstract

Temporal fluctuations of wind strength and direction can influence aeolian bedform morphology and orientation, which can be encoded into the architecture of aeolian deposits. These strata represent a direct record of atmospheric processes and can be used to understand ancient Martian atmospheric processes as well as those on Earth. The strata can: give insight to ancient atmospheric circulation, how the atmosphere evolved in response to global changes in habitability, and how ancient processes differ from modern processes. The Stimson formation at the Greenheugh pediment (Gale crater) records evidence of fluctuating wind across multiple temporal scales. The strata can be subdivided into three intervals-Gleann Beag, Ladder, and Edinburgh intervals. Internally, the intervals record changes of dune morphology and orientation, correlatable to wind fluctuations at multiple temporal scales. The basal Gleann Beag interval comprises compound cross-strata, deposited by oblique compound dunes. These dunes record a bimodal wind regime, resulting in net sediment transport toward the north. The Ladder interval records a reversal of sediment transport to the south, where straight-crested simple-dunes shaped by a seasonally variable winds formed. Finally, the Edinburgh interval records sediment transport to the west, where a unimodal wind formed sinuous-crested simple dunes. These observations demonstrate active and variable atmospheric circulation in Gale crater during the accumulation of the Stimson dune field, at multiple temporal scales from seasonally driven winds to much longer time-frames, during the Hesperian. These observations can be used to further understand ancient atmospheric conditions and processes, at a high temporal resolution on Mars.

The Aeolian Environment in Glen Torridon, Gale Crater, Mars

“…It is unclear how these winds in the past might have contributed to the evolution of Glen Torridon by abrasion and evacuation of erosional debris. Discrepancies between modern and ancient wind conditions are not uncommon on Mars (e.g., Bridges et al., 1999; Favaro et al., 2021), and these NE abrasion textures add to other evidence for significant past variability in wind direction and strength at Glen Torridon and elsewhere in Gale (e.g., Banham et al., 2018, 2021, 2022). By analogy to other locations visited by MSL on the lower flank of Aeolis Mons (Martin et al., 2021), most erosion and excavation of the Glen Torridon trough probably occurred before the onset of the Amazonian, and erosion rates in Glen Torridon likely have slowed since then due to climate changes and/or depletion of sediment supply, creating the current landscape reflecting a formerly more active aeolian environment.…”

“…Except for aeolian sandstones of the Stimson formation (Banham et al, 2018(Banham et al, , 2021(Banham et al, , 2022, Periodic Bedrock Ridges (PBRs) are interpreted as the oldest aeolian features preserved in the Glen Torridon area. PBR surfaces incorporate regional bedrock stratigraphy, indicating they are fundamentally erosional features (Stack et al, 2022), not ancient bedforms that stalled during migration then became lithified.…”

“…This model is consistent with the net‐SW and ‐SE migration of bedforms in the NW and NE regions of the crater (respectively) inferred by dune morphologies (Day & Kocurek, 2016), observed from orbit (Bridges et al., 2017; Silvestro et al., 2013, 2016), and recorded from the surface (Baker, Lapotre, et al., 2018; Baker, Newman, et al., 2018). Many rock abrasion features observed by MSL, especially those near active dunes, correlate well with ongoing dune migration directions, but other lithified wind indicators preserve evidence of different formative wind directions (Banham et al., 2018, 2021, 2022; Schieber et al., 2020). While evidence supports the important influences of regional‐scale winds from the N and local slope winds in Gale crater, the relative influence of these competing flows could have evolved over time with obliquity cycles and topographic evolution of the crater.…”

“…Downslope, the Glen Torridon trough rim is defined by the erosionally resistant, hematite-bearing Vera Rubin ridge (Fraeman et al, 2020) that stands above the trough floor with up to 7 m of local relief. Upslope, the Glen Torridon trough rim is defined by the Greenheugh pediment scarp (Banham et al, 2022;Hughes, 2021Hughes, , 2022 that rises locally as much as 15 m above the trough floor. Between the Vera Rubin ridge and the Greenheugh pediment, the Glen Torridon trough forms a natural conduit for wind-driven sand to migrate through.…”

“…The rover gradually ascended from lower parts of the Glen Torridon trough floor, crossing into the Glasgow member (faintly laminated mudstone in the Carolyn Shoemaker formation) which is stratigraphically above cross‐bedded sandstones and mudstones of the Knockfarril Hill member (Bennett et al., 2022). The Glasgow unit is in turn unconformably overlain by the Stimson formation (sandstone) of the Greenheugh pediment (Banham et al., 2022). Glasgow terrain is characterized by greater surface relief and relatively higher sand coverage; dark sand deposits fill many of the topographic lows in the area, and partly cover the steep slopes leading up to the Greenheugh pediment.…”