Glacial landscape and paleoglaciation in Terra Sabaea: Evidence for a 3.6 Ga polythermal plateau ice cap

Abstract

In a previous study, we demonstrated with a comparative morphometrical analysis the first morphometric evidence of a glacial landscape composed of glacial cirques and glacial valleys in the south of Terra Sabaea at an elevation > 1000 m in two impact craters and one mountain. The purpose of this study is to use the same method to seek other geomorphologic evidence of glacial landscapes elsewhere in Terra Sabaea. Based on a comparison between current and old glacial landscapes on Earth and Mars, we identified 81 glacial valleys and possible evidence for a former plateau ice cap dated at 3.6 Ga at the highest elevation in Terra Sabaea. The identified glacial valleys have the same morphometric properties as terrestrial and martian glacial valleys with U-shaped cross-sectional profiles, a V-index > 0.2, a length to with ratio > 1 and a cross-sectional area to drainage area ratio four times higher than the fluvial ones. Moreover, these properties are different from terrestrial and martian fluvial valleys. We did not find well preserved glacial cirques in this area, this absence questions the origin of glacial valleys. However, the presence of an extensive flat plateau, from which the long valleys radiate, could have hosted an ancient plateau ice cap which was the source of these glacial valleys. A comparison with the Cantal and the Shaluli Shan in the southeastern Tibetan plateau on Earth reveals morphometrical similarities with our study area. In fact, long glacial valleys, originating radially from a plateau at higher elevation are characteristics of an ancient plateau ice cap. This analysis allowed us to propose a polythermal regime for martian glacial landscape, namely a cold-based ice cap except at the margin where the regime is warmed-based due to the steeper topography. This topography created shear stress which increased the heat at the base of the ice and created the outlet glacial valleys. Near the plateau, the radial valleys are U-shaped with a V-index > 0.2 but downstream, to the low elevation area, these valleys become more V-shaped with a V-index around 0.1. This hypothesis is supported by the presence of an open-basin paleolake making the transition between inlet glacial valleys upstream and an outlet V-shaped valley downstream. So the morphometry of the radiating valleys suggests that liquid water played a role in the formation of this landscape.

Ancient and present surface evolution processes in the Ash region of comet 67P/Churyumov-Gerasimenko

“…In order to seek geomorphological evidence of these processes, we performed a comparative morphometrical analysis (CMA), a technique successfully used to analyze other planetary surfaces (e.g., the Earth and Mars). Based on Bouquety et al (2019Bouquety et al ( , 2020, the CMA allows us to study surface features via a morphological and geometrical approach, with a great level of detail, and to build a set of morphological parameters, which can then be used for the pre-and post-perihelion comparison investigation. All our measurements were made with the ArcGIS software.…”

Noachian Proglacial Paleolakes on Mars: Regionally Recurrent Fluvial Activity and Lake Formation within Closed-source Drainage Basin Craters

“…A body of geologic evidence suggests that Noachian-aged craters on Mars were modified primarily by rainfall-driven runoff in a warm and wet early Mars climate (Craddock et al 1997;Craddock & Howard 2002;Forsberg-Taylor et al 2004;Matsubara et al 2018). Despite suggestions of melting and runoff of frozen water ice as plausible alternatives (e.g., Craddock & Howard 2002;Moore & Howard 2005a), and support for Noachian glaciation from certain climate models (Forget et al 2013;Wordsworth et al 2013Wordsworth et al , 2015Palumbo & Head 2018;Wordsworth et al 2013), conclusive geomorphic evidence of ancient glaciation on Mars has remained sparse (Bouquety et al 2019(Bouquety et al , 2020.…”

“…If the predictions from climate models of an icy Noachian highlands are correct, then geomorphic evidence of ancient glaciation should be abundant in these areas, yet definitive evidence has been sparse (Bouquety et al 2019(Bouquety et al , 2020. Estimates of a Noachian surface/near-surface water inventory of ∼34 m global equivalent layer (GEL; Carr & Head 2015) would restrict Noachian glaciation to a scenario where the extent and thickness of glacial ice is constrained to a finite volume (Fastook & Head 2015).…”

Evidence for thermokarst depressions on comet 67P/Churyumov-Gerasimenko: An interplanetary comparison

“…The main objective of this method is to identify geometrical and morphological similarities and differences between these morphologies. We already successfully applied this technique to distinguish between glacial and fluvial erosion on Mars (Bouquety et al 2019(Bouquety et al , 2020 and to quantify the changes observed in two depressions on 67P (Bouquety et al 2021).…”