Mars Science Laboratory Observations of Chloride Salts in Gale Crater, Mars.

N H Thomas,B L Ehlmann,D E Anderson,W Rapin,N Mangold,R C Wiens,S Schröder,F Rivera‐Hernández,R Gellert,P.‐Y Meslin,A Cousin,O Forni,O Gasnault

doi:10.1029/2019gl082764

Abstract

The Mars Science Laboratory Curiosity rover is traversing a sequence of stratified sedimentary rocks in Gale crater that contain varied eolian, fluviodeltaic, and lake deposits, with phyllosilicates, iron oxides, and sulfate salts. Here, we report the chloride salt distribution along the rover traverse. Chlorine is detected at low levels (<3 wt.%) in soil and rock targets with multiple MSL instruments. Isolated fine‐scale observations of high chlorine (up to ≥15 wt.% Cl), detected using the ChemCam instrument, are associated with elevated Na2O and interpreted as halite grains or cements in bedrock. Halite is also interpreted at the margins of veins and in nodular, altered textures. We have not detected halite in obvious evaporitic layers. Instead, its scattered distribution indicates that chlorides emplaced earlier in particular members of the Murray formation were remobilized and reprecipitated by later groundwaters within Murray formation mudstones and in diagenetic veins and nodules.

Highlights

Evaporite mineral assemblages record the physical and chemical characteristics of past environments and allow us to place constraints on the chemistry of surface and subsurface fluids
In this paper we report the chlorine distribution in rocks and soils along Curiosity's traverse, using multiple instruments, in particular focusing on observations that indicate small‐scale enrichments in chloride salts, in order to inform our understanding of the depositional and groundwater environments at Gale crater
In soils the ChemCam Cl peak area varies little along the traverse, consistent with data from Alpha Particle X‐ray Spectrometer (APXS) showing ~1 wt.% Cl (Figure 1d; see O'Connell‐Cooper et al, 2017)

Summary

Introduction

Evaporite mineral assemblages record the physical and chemical characteristics of past environments and allow us to place constraints on the chemistry of surface and subsurface fluids. The Mars Odyssey Gamma Ray Spectrometer has mapped the global distribution of chlorine (Diez et al, 2009), and specific chloride‐enriched deposits were discovered in hundreds of irregular depressions in ancient terrains of the southern Martian highlands using the Mars Odyssey Thermal Emission Imaging System (Osterloo et al, 2010). These chlorides likely precipitated by evaporation from a ponded brine derived from groundwater upwelling and/or surface runoff.

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Discussion

Conclusion