The honeycomb terrain on the Hellas basin floor, Mars: A case for salt or ice diapirism

Abstract

We present quantitative plausibility studies of potential formation mechanisms for the “honeycomb” terrain on the northwestern Hellas basin floor. The honeycomb terrain is a unique landscape of ~10.5 × 5 km wide, mostly cell‐shaped depressions that are arranged in a regular, dense pattern covering ~36,000 km2. We argue against the honeycombs being (peri)glacial landforms (till rings, iceberg imprints, and thermokarst) or the result of igneous diapirism, as terrestrial analogs do not reproduce their key characteristics. Fossilized impact melt convection cells also appear to be an unsuitable interpretation, as melt solidification should not permit such structures to be retained. We present arguments in favor of salt or ice diapirism as honeycomb formation models. Honeycomb‐sized diapirs could be formed by a ~2 km thick salt layer (~72,000 km3 for the entire honeycomb terrain), which might have been derived from the highlands north of Hellas Planitia—an area of abundant chloride signatures and intense snowfall according to ancient Mars climate models. Nearby volcanic activity ~3.8 Ga ago potentially enabled recurring phases of (probably salty) meltwater runoff (as indicated by meandering channels) and might therefore have enabled evaporite deposition in the Hellas basin. Being twice as buoyant as salt, water ice would require an only ~1 km thick layer (i.e., ~36,000 km3) to form honeycomb‐sized diapirs, which would be in agreement with a likely ~2 km thick ice stability zone beneath the Hellas basin floor. However, it would remain an open question as to why we find only one such ice diapir landscape on Mars.

Evolution of major sedimentary mounds on Mars: Buildup via anticompensational stacking modulated by climate change

“…Salt diapirism before moat erosion would not lead to systematic outward dips in outcrop. Where diapirism is inferred on Mars, it has a horizontal length scale that is comparable to the thickness of the sedimentary layer, and so much less than the ~10 2 km length of the VM mounds (Bernhardt et al 2016). Faulting can and does tilt layers (Lewis & Aharonson 2014), but syndepositional basement uplifts beneath (and only beneath) mounds are unlikely.…”

Ice on Noachian and Hesperian Mars: Atmospheric, surface, and subsurface processes

“…In simulations with the same ice flow model, ice inventories, and comparable mean annual temperatures, but where mass balance was instead derived from the spatially varying potential sublimation (Wordsworth et al, 2015) predicted by the LMD MGCM, ice sheets were confined to smaller regions of the highlands, flow velocities were greater, and basal temperatures were higher (Scanlon, 2016, Fastook et al, 2021. This is especially important at Hellas and Argyre, where steeper slopes at the basin edges and warmer temperatures at lower altitudes result in relatively fast modeled flow into the basin and strong modeled basal melting within them, and could explain the prevalence of ancient, potentially glacial or glaciofluvial features reported in the two basins (Banks et al, 2009, Bernhardt et al, 2013, Dohm et al, 2015, Bernhardt et al, 2016, Bernhardt et al, 2019.…”

Progress and prospects for research on Martian topographic features and typical landform identification

“…In addition to Martian glacial landforms (beyond CCFs, LVFs, LDAs, and VFFs), periglacial landforms, such as pingos (Dundas et al, 2008;Richard et al, 2021), scallop-shaped depressions (Lefort et al, 2010), polygonal terrains (Soare et al, 2021), and thermokarst depressions (Bernhardt et al, 2016), are also present. Especially, some glacial-relevant landforms were found in the mid-latitudes of the Utopia Planitia.…”