Using Reflectance Spectroscopy to Investigate Alluvial Fan Composition in the Atacama Desert as a Hyperarid Mars Analog Environment

Session: Advancing Mineralogy and Spectroscopy Across the Solar System in Honor of MSA Roebling Medalist M. Darby Dyar

Presenting Author:

Amanda Rudolph

Authors:

Rudolph, Amanda N.¹, Wilson, Sharon A.², Davis, Joel M.³, Grant, John A.⁴, Williams, Rebecca M. E.⁵, Gehringer, Emma R.⁶, Morgan, Alexander M.⁷, Palucis, Marisa C.⁸

(1) Smithsonian Institution, National Air and Space Museum, Washington, DC, USA, (2) Smithsonian Institution, National Air and Space Museum, Washington, DC, USA, (3) Imperial College London, London, United Kingdom, (4) Smithsonian Institution, National Air and Space Museum, Washington, DC, USA, (5) Planetary Science Institute, Tucson, AZ, USA, (6) Dartmouth College, Hanover, NH, USA, (7) Planetary Science Institute, Tucson, AZ, USA, (8) Dartmouth College, Hanover, NH, USA,

Abstract:

The Atacama Desert in Chile is a hyperarid environment that is an important site for Martian evaporite analog studies to decipher the late-stage climate and aqueous history of Mars. We have performed spectroscopic analyses at the surface and with depth along exposed stratigraphic sections of eroded alluvial deposits in the northern Atacama Desert. These analyses provide insight into the compositional variability within the alluvial deposits, with mineralogical spatial and depth trends having implications for the timing of deposition and alteration. The hydrated minerals observed in these deposits are important identifiers for past aqueous activity in this modern arid environment on Earth, which can be applicable to Mars.

We are using visible-to-near-infrared (VNIR) to short-wave infrared (SWIR) reflectance spectra (0.45 to 2.5 μm) to characterize the mineral compositions that are present in these alluvial deposits. Point spectra (centimeter-scale spot size) were collected in the field using an ASD QualitySpec Trek Portable Spectrometer. To date, we have identified the presence of hydrated minerals, as almost every spectrum exhibits absorption bands near 1.4 μm and 1.9 μm that are respectively associated with OH^- and H₂O. However, the exact shape and depth of these features differ; in some cases, the 1.4 μm absorption band is a triplet absorption that is more consistent with sulfates (e.g., gypsum), while in other cases, a single narrow absorption band is observed, which is more often observed in clay mineral spectra. Additional spectral absorption features between 2.1 μm and 2.5 μm will be used to differentiate between the clay minerals and salts (e.g., sulfates, nitrates, and carbonates) that may be present in the alluvial system. The identification of specific mineral types can provide clues into their formation processes and environments. For examples, clay minerals are generally more indicative of moderate pH waters and weathering and (or) pedogenic processes, while sulfate minerals are more commonly observed in lower pH and evaporitic environments. We will further refine these analyses to constrain specific mineral compositions where possible and their spatial variability, both laterally and with depth (i.e., time). This work will help to understand the role of alteration and evaporate deposits in an arid environment and to inform similar terrains on Mars.