Formation and Preservation of Microbial Palisade Fabric in Silica Deposits from El Tatio, Chile

Abstract

Palisade fabric is a ubiquitous texture of silica sinter found in low temperature (<40°C) regimes of hot spring environments, and it is formed when populations of filamentous microorganisms act as templates for silica polymerization. Although it is known that postdepositional processes such as biological degradation and dewatering can strongly affect preservation of these fabrics, the impact of extreme aridity has so far not been studied in detail. Here, we report a detailed analysis of recently silicified palisade fabrics from a geyser in El Tatio, Chile, tracing the progressive degradation of microorganisms within the silica matrix. This is complemented by heating experiments of natural sinter samples to assess the role of diagenesis. Sheathed cyanobacteria, identified as Leptolyngbya sp., were found to be incorporated into silica sinter by irregular cycles of wetting, evaporation, and mineral precipitation. Transmission electron microscopy analyses revealed that nanometer-sized silica particles are filling the pore space within individual cyanobacterial sheaths, giving rise to their structural rigidity to sustain a palisade fabric framework. Diagenesis experiments further show that the sheaths of the filaments are preferentially preserved relative to the trichomes, and that the amount of water present within the sinter is an important factor for overall preservation during burial. This study confirms that palisade fabrics are efficiently generated in a highly evaporative geothermal field, and that these biosignatures can be most effectively preserved under dry diagenetic conditions.

Radiocarbon Dating of Silica Sinter and Postglacial Hydrothermal Activity in the El Tatio Geyser Field

“…Those organisms coexist with cyanobacteria at temperatures from 60°C to 65°C in Yellowstone, USA, and Iceland (e.g., Steinke et al, 2020; Van Der Meer et al, 2007). In El Tatio, these bacteria were found in lower temperature (~40°C) bacterial mats, with δ 13 C between −13‰ and −16‰ (Gong et al, 2020). Incorporation of inorganic carbon would yield old apparent 14 C ages as in magmatic environments with high CO 2 emissions (Evans et al, 2010).…”

The influence of microbial mats on travertine precipitation in active hydrothermal systems (Central Italy)

“…Di Benedetto et al, 2011) or to Leptolyngbya (cf. Valeriani et al, 2018; Gong et al, 2020) and to Synechococcus (Pentecost, 2003), respectively. Pentecost and Coletta (2007) identified Spirulina labyrinthiformis as the most abundant cyanobacteria from temperatures < 54°C, associated with Fischerella laminosus , Oscillatoria cf.…”

“…Nevertheless, the three sites show that there is a temperature control on the composition of the microbial mats and within the same system from proximal to distal cooled-down settings (Figure 12). Various studies have suggested a temperature control on the composition of microbial communities in hydrothermal terrestrial settings (Cady and Farmer, 1996; Farmer, 2000; Dunckel et al, 2009; Di Benedetto et al, 2011; Djokic et al, 2017; Des Marais and Walter, 2019; Sanchez-Garcia et al, 2019; Gong et al, 2020).…”

“…Pentecost, 2003). Most of these inferred cyanobacteria forms have been identified in moderate temperature (20-50°C) hydrothermal systems associated with diatoms (Pentecost, 2003; Shiraishi et al, 2019; Gong et al, 2020). In particular, Calothrix thermalis has been described in various hydrothermal vents with temperature of 20-40°C (Cady and Farmer, 1996; Farmer, 2000; Pentecost, 2003, 2005; Jones and Peng, 2015).…”

Trace Element Concentrations Associated with Mid-Paleozoic Microfossils as Biosignatures to Aid in the Search for Life

“…Sixteen microfossils from the Wobegong North sinters, located within the Conway Hydrothermal System in Drummond Basin, displaying thin-bedded palisade fabrics (a common texture of silica sinter formed by populations of filamentous microorganisms [ 26 ]), were chosen for analyses [ 24 ]. Microfossils were located and imaged via transmitted light microscopy ( Supplementary Materials ) and were analyzed via confocal laser scanning microscopy to confirm features commonly associated with microbial remains (e.g., fluorescent cell walls, hollow structure—see Figure 1 ).…”