The Physical and Chemical Sedimentology of Two High-Altitude Acid Salars in Chile: Sedimentary Processes In An Extreme Environment

Abstract

The range of environments that host acid brines has not been fully described. Salar Gorbea and Salar Ignorado are two salars in the Andes Mountains of northeastern Chile with surface and groundwater pH as low as 1.8 and salinity as high as 290% total dissolved solids (TDS). These salars are surrounded by active volcanoes and are hosted by volcaniclastic sediments. Volcanogenic groundwaters are low-temperature brines that range from extremely acid to neutral. These groundwaters are the source of waters fed upward into small pools of surface waters scattered throughout the salars. The extreme water chemistry in this arid setting leads to precipitation of an unusual assemblage of chemical sediments, including gypsum and other Ca and Mg sulfates, alunite, jarosite, halite, hematite, kaolinite, and native sulfur. Winds sculpt the salar surface, forming blowouts and large ripples and dunes. In particular, large gravel devils, as well as other wind phenomena, rework both volcaniclastic grains and chemical sediments, including gypsum crystals up to 27 cm long. Extremes in temperature cause freezing and thawing and result in cracks and buckled and puffed polygons. Microbial mats are associated with both the lowest-and highest-pH surface waters. Early diagenesis in the top few centimeters of sediment forms displacive crystals, cements, and concretions. The combination of volcanogenic setting with the extreme conditions of high elevation, high solar radiation, intense aridity, strong winds, high salinity, and low pH makes these among the most extreme surface environments on Earth. This paper provides a comprehensive documentation of the sedimentary processes and products of these rare acid salars for the first time. In addition, this study compares and contrasts salars Gorbea and Ignorado to acid saline lakes elsewhere in the world. These Chilean settings, with their acid-brine sedimentary and diagenetic minerals, strong winds, and volcanic terrain, may serve as previously undescribed terrestrial analogs for some martian and some terrestrial sedimentary systems.

Beneath the Gypsum Dunes: Cenozoic History of Wind and Water from a Core Drilled at White Sands, New Mexico

“…This unit is underlain by 6 in (15 cm) of laminated siliciclastic and overlain by approximately 7 ft (2.1 m) of laminated siliciclastic mudstones. The crystals show some similarity to splayed bottom-growth gypsum observed in Salar Ignorado and Gorbea, Chile (Benison, 2019).…”

“…Vertical orientation, widening upwards, and swallow tail shapes are characteristic habits of gypsum crystals precipitated at the sediment -water interface in saline lakes (Schreiber and Tabakh, 2001;Benison et. al., 2007;Benison, 2019).…”

How to Search for Life in Martian Chemical Sediments and Their Fluid and Solid Inclusions Using Petrographic and Spectroscopic Methods

“…Modern samples were collected by the author at acid saline lakes in southern Western Australia and northern Chile (Benison et al, 2007;Benison, 2019). Two Pleistocene (?)…”

Water Activities of Acid Brine Lakes Approach the Limit for Life

“…Modern acid brines with pH as low as 1.4 and salinity as high as 32% TDS are known from ephemeral lakes in southern Western Australia (Benison et al, 2007;Bowen and Benison, 2009;Benison and Bowen, 2015). In northern Chile, some shallow lakes have pH as low as 1.3 and salinity as high as 29.7% TDS (Risacher et al, 2002;Benison, 2019a). In contrast, modern seawater has pH of approximately 8.1 and salinity of approximately 3.5% TDS (Drever, 1997).…”