VNIR Spectral Analyses of Paleolake sediments at Lej&#237;a in the Altiplano region of Chile
Authors: Bishop Janice L. , Lezcano Vega María Ángeles , Parro Victor , Cabrol Nathalie A. , Sánchez-García Laura , Warren Rhodes Kimberly , Hinman Nancy W. 
Published: July 2021

The mineralogy of paleolake sediment strata at the high elevation (~4300 m) Lej&#237;a depression in the Altiplano region of Chile reflect evolution of the lake geochemistry over time. This mineralogical study is part of a larger project characterizing the geochemistry and biology of several samples from a paleo terrace of the Lej&#237;a lake region. Visible/near-infrared (VNIR) reflectance measurements of several samples reveal variations in gypsum, carbonate, clays, iron oxides/hydroxides, and halite with depth. The spectral features are also consistent with abundant allophane or related poorly crystalline clay phases. Mg-calcite, gypsum, and poorly crystalline clays dominate the surface materials, while each of these components varies with depth at our study site. Sediments at Gale crater on Mars also include abundant poorly crystalline phases, phyllosilicates, gypsum, halite, and iron oxides/hydroxides. Thus, characterizing the spectral properties of paleolake sediments from the Lej&#237;a region may help constrain the spectral signatures of Gale crater sediments and other sites measured from orbit.Study Site. The broader Altiplano region of Chile provides an analog for Mars due to its extremely dry and salty conditions and this study was carried out as part of the SETI Institute team&#8217;s NASA Astrobiology Institute project (Cabrol et al., 2017). The Lej&#237;a region differs from others in the Chlean Altiplano due to its higher pH environment and the presence of clay minerals and carbonates in addition to the ubiquitous gypsum and halite otherwise characteristic of the Atacama region. Laguna Lej&#237;a is a shallow, salty lake spanning ~1 km in a depression between L&#225;scar and other volcanoes in northern Chile where a larger glacial lake (10-15 km across) once stood (Grosjean et al., 1995). This high altitude basin is battered by winds and receives only limited precipitation, mostly from melting snow and ice from the surrounding mountains. Despite limited water, high UV radiation, and cold temperatures, zooplankton communities are present at Laguna Lej&#237;a (Mu&#241;oz-Pedreros et al., 2013). Further, genome-resolved metagenomics investigations are currently being developed to characterize the communities of microorganisms and their metabolisms in the paleo sediments of the Lej&#237;a lake (Lezcano et al., in preparation).Samples. The paleolake sediments investigated here were collected in 2018 from the upper 1 m of a lake terrace (Figure 1) adjacent to the current Lej&#237;a lake. The samples were kept frozen until studied. Extensive analyses are underway including X-ray diffraction (XRD), major element analyses, &#948;13C and &#948;15N isotope analyses, metagenomics, and lipid analyses (Lezcano et al., in preparation). XRD analyses determined the presence of albite, anorthite, Mg-calcite, gypsum, halite, andesine, muscovite, and quartz in many of these samples. Aliquots of 6 samples collected from different horizons were thawed, then air dried in the lab, gently crushed and dry sieved to