Tithonium Chasma on Mars: evidences for water related processes time span on Mars

Introduction: High albedo features in Valles Marineris (VM) were first identified in Mariner 9 data and ever since there has been a continuous source of debate concerning their emplacement and evolution. Tithonium Chasma (TC) system on Mars is the westernmost part of Valles Marineris (VM) that present light toned outcrops (LTO) in ambiguous relationship with plain material that cuts through. Whatever process of formation of VM (structural collapse and/or spreading tectonism) the presence of these deposits can offer the means for assessing the Martian water time span, especially the superior limit of the recently proposed wet-dry boundary for Martian global climatic transition, what is defined as ‘‘theiikian’’ era [1]. The geologic alteration timeline proposed in [1] is contrary to the observed emplacement of LTO in TC, which bear unambiguously identified hydrated sulfates and together with their relationship with the rest of the geologic units make the best evidence for the purpose of time span. Geology: TC cuts through a series of volcanic, igneous and/or sedimentary stacked material the results of several episodes of igneous activity during the several episodes of Tharsis bulge rise that produced a dome at global scale in the Martian western hemisphere. TC makes a deep chasm depression within the plateau material, which exposed to chasm walls preserving to the deepest points traces of layered deposits that makes the plateau surrounding the Chasmata. Ius Chasma opens parallel to the south, cutting dipper into plateau isolating an older Hesperian fractured (Hf) material island in-between [2], being surrounded to North and South of western VM canyon system by the geologic unit Hsu figure 1. The Hsu geologic unit is the youngest deposited material along any of the VM chasm and according to stratigraphic cross-cutting relation relatively defines the time of western VM Chasmata formation as posteriori to Hsu unit emplacement. The LTO deposits dominate the central parts of TC west and the smaller chasm of TC east, their presence within chasm as well as the presence of sulfates in many of LTO’s changes the time of deposition according to the stratigraphic relationship with the walls, as well as giving a longer time span to the processes involved in their emplacement. They are strongly eroded into flutes, alcoves, and yardangs and show almost no impact craters at their surface, attesting either an easily erodible rock material, a young geologic formation, or a recent exposure (exhumation) of an older material. There are two main “trends” of proposed hypothesis of formation all involving different processes, up to the moment when hydrated Mg and Ca sulfates where identified using NIR spectral signatures of hyperspectral cameras aboard OMEGA ESA Mars Express [Gendrin], [Bibring] and confirmed with CRISM on NASA MRO orbiter, when hypothesis of processes involving large amount of water prevailed the waterless ones.