Silica deposits on Mars with features resembling hot spring biosignatures at El Tatio in Chile

Abstract

The Mars rover Spirit encountered outcrops and regolith composed of opaline silica (amorphous SiO2·nH2O) in an ancient volcanic hydrothermal setting in Gusev crater. An origin via either fumarole-related acid-sulfate leaching or precipitation from hot spring fluids was suggested previously. However, the potential significance of the characteristic nodular and mm-scale digitate opaline silica structures was not recognized. Here we report remarkably similar features within active hot spring/geyser discharge channels at El Tatio in northern Chile, where halite-encrusted silica yields infrared spectra that are the best match yet to spectra from Spirit. Furthermore, we show that the nodular and digitate silica structures at El Tatio that most closely resemble those on Mars include complex sedimentary structures produced by a combination of biotic and abiotic processes. Although fully abiotic processes are not ruled out for the Martian silica structures, they satisfy an a priori definition of potential biosignatures.

Large‐scale fluid‐deposited mineralization in Margaritifer Terra, Mars

“…Biosignatures such as microbial fossils [Lynne et al, 2008;Preston et al, 2008], biotically mediated structures [Potter-McIntyre et al, 2014;Ruff and Farmer, 2016], and body molds [Guidry and Chafetz, 2003;Potter-McIntyre et al, 2017] are found preserved in precipitates from both hot and cold settings on Earth, particularly if, as at Margaritifer, they have not been subject to deep burial diagenesis. Biosignatures such as microbial fossils [Lynne et al, 2008;Preston et al, 2008], biotically mediated structures [Potter-McIntyre et al, 2014;Ruff and Farmer, 2016], and body molds [Guidry and Chafetz, 2003;Potter-McIntyre et al, 2017] are found preserved in precipitates from both hot and cold settings on Earth, particularly if, as at Margaritifer, they have not been subject to deep burial diagenesis.…”

“…Candidate sites include fault ridge traces [Treiman, 2008] and chemically altered joints [Okubo and McEwen, 2007] in Valles Marineris, and ridge networks across the equatorial region [Saper and Mustard, 2013;Kerber et al, 2017]. Structures within Vernal crater [Allen and Oehler, 2008 Gusev crater [Ruff and Farmer, 2016] and Syrtis Major [Skok et al, 2010] have been inferred to be hot spring related. Evidence for subaerial deposition has also been reported: for example, interior layered deposits within Valles Marineris and elsewhere and crater mounds such as at Crommelin crater have been attributed to cold spring deposition [Rossi et al, 2008;Franchi et al, 2014].…”

Extant shore-platform stromatolite (SPS) assemblage

“…These terraces may have been formed by wave action in the Gusev Palaeolake or at the margin of the Great Northern Ocean. The proposed siliceous stromatolites around "Home Plate" (Ruff & Farmer, 2016) were previously interpreted as hydrothermal deposits (Squyres et al, 2008), but this does not preclude them being stromatolites. It is possible that these features are extraterrestrial 5 palaeo-SPS.…”

“…2016), could be shore platform candidates and should be targets for stromatolite investigation. Recently Ruff & Farmer (2016) suggested that structures in the Ma'Adim terraces within the Gusev Crater are siliceous stromatolites. These terraces may have been formed by wave action in the Gusev Palaeolake or at the margin of the Great Northern Ocean.…”

The extant shore platform stromatolite (SPS) facies association: a glimpse into the Archean?

“…Although no shore platforms have been reported (Banfield et al, 2015) as yet, the terrain at Chryse Planitia and Arabia Terra, which border the postulated Vastitas Borealis Ocean (Wilson et al, 2016;Rodriguez at al., 2016), could be shore platform candidates. Recently Ruff and Farmer (2016) suggested that structures in the Ma'Adim terraces within the Gusev Crater are siliceous stromatolites. These terraces may have been formed by wave action in the Gusev Palaeolake or at the margin of the Vastitas Borealis Ocean and may be an extraterrestrial palaeo-SPS environment.…”