Inverted fluvial features in the Aeolis/Zephyria Plana region, Mars: Formation mechanism and initial paleodischarge estimates

摘要

A subset of the sinuous ridges (SRs) in the Aeolis/Zephyria Plana (AZP) region of Mars has been previously hypothesized to be inverted fluvial features, although the precise induration and erosion mechanisms were not specified. Morphological observations and thermal inertia data presented here support this hypothesis. A variety of mechanisms can cause inversion, and identification of the specific events that lead to fluvial SR formation can provide insights into the sedimentological, geochemical, and climatic processes of the region. Reconnaissance of two terrestrial lava-capped ridges suggests some criteria that may be used to identify inverted fluvial features formed by lava infill on Mars, but these criteria are not satisfied by the majority of the AZP fluvial SRs. Armoring also appears inconsistent with terrestrial analogs. Layering and surface textures of fluvial SRs indicate that the most likely induration mechanism was geochemical cementation of fluvial sediments, and that the primary erosional mechanism that exposed the fluvial SRs was aeolian abrasion. This analysis of formation mechanism provides a foundation for estimating paleodischarge using an empirical form-discharge approach, to which we have applied scaling, for Martian gravity. For those fluvial SRs meeting a set of criteria for accurate paleodischarge estimates, paleodischarge values generally range between 10~1 and 10~3 m~3 s~(-1). The largest of these initial estimates are comparable to paleodischarge estimates for some late-stage Noachian fluvial channels on Mars, and provide a constraint on the atmospheric conditions at this equatorial location during the late Hesperian to early Amazonian time frame.