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Morphologie et remplissage sédimentaire des vallées martiennes : marqueurs des conditions climatiques pré-amazoniennes

Abstract : Nowadays Mars has a cold and dry climate. At some locations its surface is more than 3.5 Gy old and exhibits valleys, channels, terraces and deltas attesting the occurrence of liquid water in the past. This fluid is currently unstable on the surface of the planet, suggesting these morphologies would involve different climatic conditions from the current ones. What did early Martian climate look like? It is one of the main issues regarding this planet. Among the geomorphic evidence classically used to reconstruct past climates, Martian valleys are numerous and heterogeneously thus particularly attractive to study. Their morphologies can inform on the climatic conditions prevailing at the time of their formation and/or later during their evolution. The objective of this thesis is to contribute to solve the enigma concerning Martian pre-Amazonian (> 3.5Gy) climatic conditions by focusing on the study of equatorial valleys and the equatorial canyon of Valles Marineris. Our study reveals that the morphometry and spatial organization of some Martian valleys differ significantly from those of common terrestrial fluvial and sapping valleys. By contrast, they share a lot of similarities with terrestrial subglacial tunnel valley. The subglacial or pro-glacial melting of surface ice deposits is plausible as an origin of some Martian valleys under cold climatic conditions. Moreover, regional geomorphological reconstitutions of Valles Marineris reveal that this valley system had witnessed glacial processes since its formation. Current glacial relicts of this former filling, probably several billion years old, still, subsist protected under a debris cover. This study suggests the possibility that pre-Amazonian atmospheric conditions on Mars do not require to be significantly different from the current ones.
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Submitted on : Sunday, May 10, 2020 - 6:03:18 PM
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Marine Gourronc. Morphologie et remplissage sédimentaire des vallées martiennes : marqueurs des conditions climatiques pré-amazoniennes. Planétologie. Université de Nantes (Unam), 2015. Français. ⟨tel-02568956⟩

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