Sporadic Groundwater Upwelling in Deep Martian Craters: Evidence for Lacustrine Clays and Carbonates

While the surface of Mars may have had an active hydrosphere early in its history [1], it is likely that this water retreated to the subsurface early on due to loss of the magnetic field and early atmosphere [2]. This likely resulted in the formation of two distinct aqueous regimes for Mars from the Late Noachian onward: one dominated by redistribution of surface ice and occasional melting of snow/ice [3], and one dominated by groundwater activity [4]. The excavation of alteration minerals from deep in the crust by impact craters points to an active, ancient, deep hydrothermal system [5]. Putative sapping features [6] may occur where the groundwater breached the surface. Upwelling groundwater may also have played a critical role in the formation of massive, layered, cemented sediments in Sinus Meridiani [7,8], in the Valles Marineris [9], and possibly in Gale Crater [10], where the Curiosity Rover will land later this year. Understanding the past distribution, geochemistry, and significance of groundwater on Mars is critical to untangling the origins of deep alteration minerals, Hesperian sulfate deposits, and crater fill deposits at Gale Crater or in other locations.