Formation of double‐layered ejecta craters on Mars: A glacial substrate model

Abstract

[1] A class of Martian impact craters with particularly unusual ejecta characteristics (double-layered ejecta (DLE) craters) are preferentially located in the midlatitudes in both hemispheres of Mars. Unlike today, decameters thick deposits of snow and ice occupied these same latitudes for significant periods during the Amazonian period. We assess the hypothesis that the unusual double-layer morphology could be related to impact into a snow and ice glacial substrate followed by landsliding of ejecta off of the structurally uplifted rim. We find that many characteristics of DLE craters (e.g., latitudinal distribution, lack of secondaries, landslide-like textures, evidence for overthrusting, relation to other crater types, etc.) are consistent with such an origin. Citation: Weiss, D. K., and J. W. Head (2013), Formation of double-layered ejecta craters on Mars: A glacial substrate model, Geophys. Res. Lett., 40,[3819][3820][3821][3822][3823][3824]

Expanded secondary craters in the Arcadia Planitia region, Mars: Evidence for tens of Myr-old shallow subsurface ice

“…Since the time for degradation to occur is identical, different secondary crater morphologies within a given secondary crater field can indicate variations in surface and subsurface conditions that can be explored over large spatial extents. Secondary crater fields appear to be rare at higher latitudes on Mars (Boyce and Mouginis-Mark, 2006), perhaps related to sublimation of ice (Weiss and Head, 2013). Arcadia Planitia is the exception, where we have found four craters with diameters ranging from 6 to 20 km, all with well-preserved secondaries.…”

Using martian single and double layered ejecta craters to probe subsurface stratigraphy

“…Thickness estimates for the past ice-sheet deposited in the northern mid-latitudes during higher obliquity are on the order of hundreds of metres from climate models (Madeleine et al, 2009), which is generally consistent with glacial morphologies in the region. For example, lobate debris aprons and lineated valley fill may indicate ice-rich glacial deposits once 100s of metres thick (Fastook et al, 2011;Plaut et al, 2009); and pedestal, excesses ejecta and perched crater morphologies in these latitudes are also suggestive of formation within an ice-rich layer 50-150 m thick (Black and Stewart, 2008;Kadish et al, 2009;Meresse et al, 2006;Weiss and Head, 2013). Furthermore, analyses of the latter morphologies suggest the volatile-rich layer may superimpose a rocky regolith beneath Fig.…”

“…Craters with more than one fluidized layer of ejecta are typically thought to originate from a multi-layered target, as a result of a gradient in volatile content and/or particle size distribution (Boyce and Mouginis-Mark, 2006;Horner and Greeley, 1981;Stewart and Valiant, 2006;Weiss and Head, 2013;Wulf et al, 2013). Both impact modelling (Collins et al, 2002;Senft and Stewart, 2008) and observations of terrestrial craters (Osinski et al, 2011) demonstrate that variations in target stratigraphy result in significant and measureable effects on the resulting final crater, particularly in the maximum runout distance of ejecta, the topographic profile of the ejecta blanket, the crater depth, and the size of the central uplift.…”

Inferring the high velocity of landslides in Valles Marineris on Mars from morphological analysis

“…However, exposed ice in the form of a glacier might be problematic in terms of thermodynamical stability of ice on equatorial Mars; moreover, the deposits would have been displaced by subsequent ice flow (De Blasio 2011a). Multiple landslides fallen on previous deposits of VM exhibit longitudinal furrows, which is compatible with ice within the regolith, rather than exposed (or at least a debris-covered glacier); similar furrows are observed on the multi-layered ejecta of impact crater at middle and low latitudes (Weiss and Head 2013). This might confirm the likely role of ice in the inertial movement of the rock.…”