Surface Morphologies in a Mars-Analog Ca-Sulfate Salar, High Andes, Northern Chile

Nancy W Hinman,Cinthya Tebes-Cayo,Nora Noffke,Philippe Sarazzin,Kevin L Rhodes,Nathalie A Cabrol,David Wettergreen,Cecilia Demergasso,Michael Mcinenly,David P Summers ,Eva V Acosta Rodríguez ,Óscar Cabestrero ,Jeffrey E Moersch ,Michael Phillips ,Guillermo Chong Dı́az ,P Sobrón ,V C Gulick ,Michaël Hofmann ,C Contreras ,K Warren-Rhodes ,J L Bishop ,Vı́ctor Parro

doi:10.3389/fspas.2021.797591

Abstract

Salar de Pajonales, a Ca-sulfate salt flat in the Chilean High Andes, showcases the type of polyextreme environment recognized as one of the best terrestrial analogs for early Mars because of its aridity, high solar irradiance, salinity, and oxidation. The surface of the salar represents a natural climate-transition experiment where contemporary lagoons transition into infrequently inundated areas, salt crusts, and lastly dry exposed paleoterraces. These surface features represent different evolutionary stages in the transition from previously wetter climatic conditions to much drier conditions today. These same stages closely mirror the climate transition on Mars from a wetter early Noachian to the Noachian/Hesperian. Salar de Pajonales thus provides a unique window into what the last near-surface oases for microbial life on Mars could have been like in hypersaline environments as the climate changed and water disappeared from the surface. Here we open that climatological window by evaluating the narrative recorded in the salar surface morphology and microenvironments and extrapolating to similar paleosettings on Mars. Our observations suggest a strong inter-dependence between small and large scale features that we interpret to be controlled by extrabasinal changes in environmental conditions, such as precipitation-evaporation-balance changes and thermal cycles, and most importantly, by internal processes, such as hydration/dehydration, efflorescence/deliquescence, and recrystallization brought about by physical and chemical processes related to changes in groundwater recharge and volcanic processes. Surface structures and textures record a history of hydrological changes that impact the mineralogy and volume of Ca-sulfate layers comprising most of the salar surface. Similar surface features on Mars, interpreted as products of freeze-thaw cycles, could, instead, be products of water-driven, volume changes in salt deposits. On Mars, surface manifestations of such salt-related processes would point to potential water sources. Because hygroscopic salts have been invoked as sources of localized, transient water sufficient to support terrestrial life, such structures might be good targets for biosignature exploration on Mars.

Highlights

The Andean Salar de Pajonales (3,537 m asl, 25o08′40′′ S, 68o49′12′′ W; Figure 1) is an evaporitic basin located on the western margin of the High Andes in the Altiplano1
The hydrological progression from active lagoons to exposed salt paleoterraces forms a natural climate-transition experiment, where each salar surface represents a different stage of evolution in the wet-to-dry transitions duringcycles of climate change over geological time scales
The climate transition exemplified at Salar de Pajonales partly mirrors that postulated for early Mars (Kite, 2019; Wordsworth et al, 2021), making it a unique terrestrial analog for early climate change on that planet (Cabrol et al, 2009; Cabrol et al, 2010; Cabrol, 2018; Farías and Acuña, 2020; Pueyo et al, 2021)

Summary

Introduction

The Andean Salar de Pajonales (3,537 m asl, 25o08′40′′ S, 68o49′12′′ W; Figure 1) is an evaporitic basin located on the western margin of the High Andes in the Altiplano. The Andean Salar de Pajonales (3,537 m asl, 25o08′40′′ S, 68o49′12′′ W; Figure 1) is an evaporitic basin located on the western margin of the High Andes in the Altiplano1 At present, it is in the desiccation period of wetting and drying cycles, comprising lagoons/salt ponds, salt crusts, infrequently inundated areas, and dry exposed paleoterraces (Chong Diaz et al, 2020). The hydrological progression from active lagoons to exposed salt paleoterraces forms a natural climate-transition experiment, where each salar surface represents a different stage of evolution in the wet-to-dry transitions during (micro-)cycles of climate change over geological time scales. The thin atmosphere produces sudden and sharp daily temperature (T) and relative humidity (Warren-Rhodes et al, in review; Kereszturi et al, 2020) fluctuations that generate high UV/ T ratios further extending the Salar de Pajonales region’s environmental analogies to Martian conditions

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Discussion

Conclusion