Abstract
We present a systematic, metre-scale characterisation of the 3D morphometry of an esker on Mars, and the first attempt to reconstruct the multi-stage dynamics of esker formation on Mars. Eskers are sinuous ridges comprising sediment deposited by meltwater draining through ice-confined tunnels within or beneath glaciers. Detailed morphometric insights into eskers on Mars are important for (i) informing morphometric tests of whether sinuous ridges elsewhere on Mars are eskers, and (ii) informing modelling experiments which aim to reconstruct the glaciological and environmental controls on esker formation on Mars. We use a digital elevation model generated from High Resolution Imaging Science Experiment (HiRISE) images to characterise the height and width of an extremely rare esker associated with a late-Amazonian-aged viscous flow feature (debris-covered glacier) in NW Tempe Terra, Mars. Our measurements suggest that the NW Tempe Terra esker is a ‘stacked’ formation comprising an underlying ‘lower member’ ridge that is superposed by a narrower ‘upper member’ ridge. We used a novel morphometric approach to test whether the apparent stacking records two distinct esker deposition regimes (either within the same drainage episode, or within temporally-separated drainage episodes). This approach posits that esker crest morphology is controlled by primary esker formation processes and, by extension, that portions of eskers with similar crest morphologies should have similar morphometric relationships. We predicted the morphometric relationships described by the constituent upper and lower member ridges based on ‘reference relationships’ observed for morphologically-similar portions of the esker where no evidence of stacking was observed. Our observations corresponded well with the predicted relationships, supporting our stacked esker hypothesis. We propose conceptual models, which invoke spatial and temporal variations in sediment supply and meltwater discharge, to explain the stacked morphology. These models are informed by morpho-sedimentary relationships observed along eskers on Earth.
Highlights
IntroductionSinuous ridge landforms in the Phlegra Montes (162.96◦E, 32.68◦N; Gallagher and Balme, 2015) and NW Tempe Terra (83.06◦W, 46.17◦N; Butcher et al, 2017) regions of Mars’ north-ern mid-latitudes have been interpreted as eskers based on their morphologies and associations with glacial landsystems, including extant debris-covered glaciers (viscous flow features, VFF; Gallagher and Balme, 2015; Butcher et al, 2017)
Sinuous ridge landforms in the Phlegra Montes (162.96◦E, 32.68◦N; Gallagher and Balme, 2015) and NW Tempe Terra (83.06◦W, 46.17◦N; Butcher et al, 2017) regions of Mars’ north-ern mid-latitudes have been interpreted as eskers based on their morphologies and associations with glacial landsystems, including extant debris-covered glaciers
In the analyses that follow (Sections 4.3 and 4.4), we demonstrate that this complexity is probably an artefact of stacking of two morphologically-distinct esker ridges under a multistage deposition regime (Section 5)
Summary
Sinuous ridge landforms in the Phlegra Montes (162.96◦E, 32.68◦N; Gallagher and Balme, 2015) and NW Tempe Terra (83.06◦W, 46.17◦N; Butcher et al, 2017) regions of Mars’ north-ern mid-latitudes have been interpreted as eskers based on their morphologies and associations with glacial landsystems, including extant debris-covered glaciers (viscous flow features, VFF; Gallagher and Balme, 2015; Butcher et al, 2017). Mars’ geologic history (Gallagher and Balme, 2015; Butcher et al, 2017) Both eskers are located within tectonic rift/graben valleys. These geologic contexts, combined with the results of modelling experiments, suggest that locally-elevated geothermal heat flux was a pre-requisite for geologically-recent basal melting of glacial ice on Mars (Gallagher and Balme, 2015; Butcher et al, 2017; Arnold et al, 2019; Sori and Bramson, 2019). Based on insights from eskers on Earth (Section 5.1; e.g., Banerjee and McDonald, 1975; Brennand, 1994; Burke et al, 2008, 2010, 2012, 2015; Perkins et al, 2016), we develop conceptual models for the possible sediment-discharge dynamics of meltwater drainage episode(s) that could explain the observed morphometries and esker stacking (Section 5.2)
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