1. McDonnell Center for the Space Sciences and the Department of Earth and Planetary Sciences, Washington University, St Louis, Missouri 63130, USA
2. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. Present address: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Correspondence to: Jeffrey C. Andrews-Hanna^1,3 Correspondence and requests for materials should be addressed to J.C.A.-H. (Email: jhanna@mit.edu).

Abstract

The Opportunity Mars Exploration Rover found evidence for groundwater activity in the Meridiani Planum region of Mars^{1, 2} in the form of aeolian and fluvial sediments³ composed of sulphate-rich grains. These sediments appear to have experienced diagenetic modification in the presence of a fluctuating water table^{3, 4, 5}. In addition to the extensive secondary aqueous alteration, the primary grains themselves probably derive from earlier playa evaporites^{1, 2, 4}. Little is known, however, about the hydrologic processes responsible for this environmental history—particularly how such extensive evaporite deposits formed in the absence of a topographic basin. Here we investigate the origin of these deposits, in the context of the global hydrology of early Mars, using numerical simulations, and demonstrate that Meridiani is one of the few regions of currently exposed ancient crust predicted to have experienced significant groundwater upwelling and evaporation. The global groundwater flow would have been driven primarily by precipitation-induced recharge and evaporative loss, with the formation of the Tharsis volcanic rise possibly playing a role through the burial of aquifers and induced global deformation. These results suggest that the deposits formed as a result of sustained groundwater upwelling and evaporation, rather than ponding within an enclosed basin. The evaporite formation coincided with a transition to more arid conditions⁶ that increased the relative impact of a deep-seated, global-scale hydrology on the surface evolution.

1. McDonnell Center for the Space Sciences and the Department of Earth and Planetary Sciences, Washington University, St Louis, Missouri 63130, USA
2. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. Present address: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Correspondence to: Jeffrey C. Andrews-Hanna^1,3 Correspondence and requests for materials should be addressed to J.C.A.-H. (Email: jhanna@mit.edu).

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