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Formation et évolution des structures périglaciaires en contexte de réchauffement climatique : comparaison Terre-Mars

Abstract : On Earth, periglacial regions where an ice-rich permafrost is present provide a record of global climate changes. For example, the ice-rich permafrost (50-80 % of ice by volume) that occurs in Central Yakutia (Siberia) and in the Mackenzie River Delta (Canada) was formed during the glacial periods of the Pleistocene. This permafrost was subsequently degraded during global warming at the early Holocene interglacial period.Global and possibly ice-rich permafrost occurs on Mars as well. It is thought to be the product of obliquity-driven and relatively recent global climate change (i.e. dozens of Ma). Utopia Planitia, situated in the northern mid-latitudes, is dotted with possible periglacial landforms (scalloped depressions, polygons and polygon-junction pits) that could indicate the presence of an ice-rich permafrost. Similarly to Earth, this permafrost could be marker of recent global climate changes.This thesis focuses on the impact of global climate changes on the periglacial regions of Earth and Mars. With this aim in view, we conducted (i) field studies of the periglacial processes and landforms in the Central Yakutia (Siberia) and in the Mackenzie River Delta (Canada) and, (ii) a geomorphological study (based on high-resolution images) of the putative-periglacial landforms of Utopia Planitia.Our study shows that the assemblage of landforms in Utopia Planitia share traits of form, scale and spatial association with the landforms of the Central Yakutia and of the Mackenzie Delta (thermokarst lakes, polygons and polygon-junction ponds) indicating that Utopia Planitia has an ice-rich permafrost. The permafrost is composed of stratified sediments ~ 70 m thick with a high ice-content (possibly ≥ 50 % by volume).The permafrost appears to have a syngenetic origin: it was formed by an accumulation of sediments in the basin of Utopia Planitia under cold climate conditions that leaded to the in-situ freezing of the sediments. The sediments could have been deposited by outflow valleys from Elysium Mons and/or by an eolian activity. With regard to the latter, the synchronous formation of a possible regional ice-sheet near Utopia Planitia during medium-obliquity (~ 35°) periods of Mars could have induced a preferential eolian deposition in Utopia Planitia.Subsequently, the ice-rich permafrost was regionally degraded between ~ 5 and 10 Ma. The thermokarst was triggered by an increase of insolation during high-obliquity (~ 45°) periods of Mars. The increase of temperature caused the thermal destabilization of the permafrost inducing the sublimation of ground-ice, deeply modifying the landscape.Thus, important obliquity variations of Mars caused global climate changes that could have induced the formation and the degradation of the ice-rich permafrost of Utopia Planitia between ~ 5 and 10 Ma.
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Antoine Séjourné. Formation et évolution des structures périglaciaires en contexte de réchauffement climatique : comparaison Terre-Mars. Sciences de la Terre. Université Paris Sud - Paris XI, 2011. Français. ⟨NNT : 2011PA112287⟩. ⟨tel-00713531⟩

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