Salts and clays beneath surface sediments in antarctica provide clues to weathering and geochemistry on mars

The McMurdo Dry Valleys (MDV) in Antarctica have long served as a process analog for Mars due to their cold and xeric conditions [1]. Liquid water is unstable on the surface most of the year [2], yet life is abundant [3]. This study focuses on the sediments and minerals that formed due to liquid water activity at a transient pond site. Understanding aqueous alteration in the cold and xeric MDV environment provides guidelines for the geochemical history of Mars that led to formation of the currently observed phyllosilicates and sulfates [e.g. 4]. Introduction: A multitude of climatic and geological factors make the MDV an excellent analog for Martian environments. The climate is extremely cold and dry with mean annual temperatures of -18°C [1,2] and minimal snowfall (<10 cm per year with sublimation >50 cm per year) [1,3]. Despite this, liquid water does occur, due to glacial meltwater and deep groundwater [3,4]. Most of the lakes, ponds and streams are highly saline, providing a direct analogue for runoffand groundwater-fed saline bodies of water inferred to have existed on Mars to produce the observed surface minerals [e.g. 4-6]. Ferrar dolerite rich in pyroxene, feldspars and phyllosilicates is pervasive in the sandstone mountains of the MDV [7,8] and serves as an analog for igneous lithologies on Mars. Weathered dolerite and sediments thus provide an analog for the martian regolith. Study Site: We studied the geochemistry, mineralogy, and spectral properties of sediments collected in 1980 at multiple depths from an intermittent pond site (VXE-6 pond) in the South Fork of Wright Valley (Fig. 1). VXE-6 pond is proximal to the chemically unique Don Juan Pond (Fig. 1) and is fed by shallow groundwater. We analyzed sediments from six depth intervals (0-1, 1-4, 4-7, 8-10, 12-15, 20-24 cm) in a pit dug at the site that was dry during sampling [9]. Previous analyses observed elevated gypsum at a depth of 8-10 cm [10]. Methods: Samples were available as coarse sediment grains in their original form as collected (C) and finely-crushed particles prepared in 1983 [9] (F). We ground and dry sieved <150 μm aliquots (G) of the bulk grains in 2018 for comparison with the previously ground material. Visible/near-infrared (VNIR) reflectance spectra of samples were collected at ambient conditions with an ASD spectrometer at the SETI Institute, while bidirectional reflectance spectra from 0.32.55 μm and FTIR reflectance spectra from 1-50 μm were collected under controlled dry conditions at the RELAB facility at Brown University, following procedures as in [11]. Major element geochemical analysis was conducted by X-ray Fluorescence (XRF) at the Bureau Veritas in Vancouver and by Instrumental Neutron Activation Analysis (INAA) at the University of Vienna.